Particulate organic matter as a functional soil component for persistent soil organic carbon

Soil pH and total phosphorus regulate bacterial community assembly in slope restoration areas of the Tibetan Plateau's metal mining areas

Microbial community development is a crucial aspect of soil restoration. The employment of frame beams in conjunction with external soil has demonstrated efficacy in the rehabilitation of degraded roadside ecosystems within mining regions. Nonetheless, the effects of frame beams on the composition and stability of soil bacterial communities remain inadequately comprehended. We conducted a one-time soil sampling on a three-year restored slope in a large-scale metal mining area on the Tibetan Plateau, providing a snapshot of the current conditions and evaluating the restoration progress. Frame beams with external soil covers were applied at three different altitudes: A1 (4800-5000 m), A2 (4500-4700 m), and A3 (4200-4400 m). Restoration significantly altered bacterial community composition compared with controls. Proteobacteria had a higher relative abundance in the restoration area (average: 31.16 %), whereas Acidobacteriota were more abundant in the control area (average: 24.68 %). In the restoration area, soil bacterial α-diversity increased as elevation decreased, with the Shannon index rising from 5.34 (A1) to 5.82 (A3), suggesting that bacterial communities at higher altitudes are more sensitive to environmental conditions. Species turnover was the primary driving factor of β-diversity, accounting for 96.26 % under A1, 94.71 % under A2, and 91.94 % under A3, respectively. The nearest taxon index of bacterial communities shifted from negative to positive along the elevation gradient (-0.25 to 1.14), indicating an increasing trend toward community clustering. Within the bacterial co-occurrence network, soil pH and total phosphorus contribute significantly to network strength, closeness, and betweenness. Concluding, soil pH and total phosphorus were identified as key factors shaping bacterial diversity and assembly mechanisms. Our research contributes to the development of effective soil restoration strategies for alpine mining regions, providing insights into microbial community assembly and stability mechanisms.

Nanoscale and molecular evidences for adsorptive fractionation of dissolved organic matter at the interfaces of Al-bearing ferrihydrite and water

Ferrihydrite (Fh) usually exists in the form of Al-bearing Fh in soils and sediments, and Al substitution may have a remarkable influence on Fh characteristics, controlling its reaction with dissolved organic matter (DOM). Yet, little is known about the impacts of Al-bearing Fh on the fate of DOM. Here, selective binding and molecular fractionation of DOM was investigated at the interfaces of Al-bearing Fh and water. Al substitution altered surface properties such as point of zero charge (PZC), surface OH groups, and specific surface areas (SSA), structure, composition, and adsorption capacity of Fh. Specifically, within 30 mol% Al substitution, Al entered into ferrihydrite structure by isomorphous substitution to form Al-substituted ferrihydrite and immobilized DOM increased with Al substitution owing to increasing surface OH groups, SSA, and pore volumes. Once the amount of added Al exceeds 30 mol%, gibbsite was formed except for Al-substituted Fh, and adsorbed DOM decreased with Al addition. The coordination environment of Al-substituted Fh consisted of Fe-O and edge- and corner-sharing FeO6 octahedral. Microscopic analysis at nanoscale disclosed that DOM was evenly distributed within Al-bearing Fh aggregates and on gibbsite surface, and DOM immobilized within Al-bearing Fh nanopores had a higher oxidation state. Mass spectrometry analysis at molecular scale revealed that compared with gibbsite, high molecular weight substances and substances containing more oxygenated groups or highly in unsaturation preferentially bound to Al-bearing Fh, and Fh with 30 mol% Al substitution induced most pronounced molecular fractionation. Collectively, these findings shed novel insights into the impact of Al substitution on interfacial adsorptive fractionation of DOM, contributing to in-depth understanding geochemical cycling of C and predicting organic C cycling across aquatic-terrestrial interfaces.

Management of soil-related ecosystem services in semi-arid regions of Iran using key environmental drivers

Soil is the most important resource for meeting the needs of the world's population. Sustainability of soil-related ecosystem services (SRES) is the primary indicator for sustainable food security. Since there are complex relationships between services, it is essential to understand the environmental and management drivers for robustness of SRES. The importance of drivers varies in the interactions between services. Four SRES i.e. soil retention, climate regulation, water regulation, and soil formation have been quantified in the semi-arid ecosystems of Iran. The findings demonstrated that the potential of land covers to provide SRES varied (p < 0.05). SRES exhibited strong synergy relations (p < 0.01), except soil formation and water regulation, which displayed a weak positive correlation (R2 = 0.0342, p > 0.05). The Bayesian networks (BNs) is a perfect tool to identify the most important environmental and management drivers influencing SRES due to its ability to model complex systems and uncertainties. BNs showed that elevation as the most important drivers influenced 15 % of the production of SRES. For sustainable management of semiarid ecosystems, the primary drivers of the pairwise relationships of SRES were identified. The NPP threshold (1.2 t ha-1) was found to be essential for maintaining soil formation and climate regulation. Richness threshold (10-15 plant species) was crucial for maintaining soil retention and water regulation. Our finding indicated a theoretical support for biodiversity management and shrub conservation in respect to strong SRES relations. Therefore, enhancing the species richness especially species with higher NPP should be the primary goal of the environmental management to maximize SRES benefit in arid lands in the future.

Synergistic interplay of management practices and environmental factors in shaping grassland soil carbon stocks: Insights into the effects of fertilization, mowing, burning, and grazing

Grasslands, which account for over 40 % of the Earth's terrestrial area, play a vital role in mitigating global change and biodiversity loss. These ecosystems serve as critical carbon sinks, regulating the global carbon cycle and supporting diverse flora and fauna. However, their ability to sustain these functions is threatened by land use change and climate disruption. Current challenges revolve around understanding how key management practices such as grazing, mowing, burning, and fertilization, interact with environmental factors to influence grassland soil carbon stocks. This study presents a meta-analysis of the effects of these management practices and environmental factors, such as soil type, depth, texture, temperature, precipitation, and their synergistic interplay. It evaluates how management intensity, duration, and frequency interact with these environmental variables to influence soil carbon storage, providing valuable insights into optimizing grassland management for enhanced soil carbon stock and broader ecosystem stability. The findings reveal that grazing, particularly at high intensity, tends to reduce soil carbon stocks (-0.412, p < 0.001), with the most pronounced effects observed in shallow soils and temperate climates. Mowing also negatively affected carbon stock (-0.416, p = 0.013), especially when carried out frequently and over long durations. On the other hand, burning had mixed results with an overall positive effect (0.340, p = 0.078). Short-term burns promoted carbon accumulation, while frequent burning led to carbon loss. Fertilization, especially with nitrogen and phosphorus, proved beneficial for increasing soil carbon stocks (0.712, p < 0.001), particularly in nutrient-poor soils and semi-arid climates. This study introduces a systems-based approach to grassland management, providing a framework for optimizing carbon-focused strategies. By integrating the role of management practices, particularly their frequency, intensity, and duration, along with soil characteristics and climate, these findings provide actionable insights for policymakers, land managers, and researchers. They guide the development of sustainable management strategies that not only enhance soil carbon stocks but also support ecosystem health and resilience.

Different Land Use Systems in the Brazilian Cerrado and Their Effects on Soil Bacterial Communities

The effect of agricultural practices on soil bacterial communities is not constant and depends a lot on the climatic context, changes in the soil characteristics, land use, and agricultural strategy. Thus, knowledge about how different land use systems in the Cerrado influence the diversity and taxonomic structure of microbial communities under the same soil type remains limited. In this context, the objective of this work was to analyze and compare the bacterial communities of Cerrado soil under two different land use systems (cover crop and potato cultivation) and in a neighboring native Cerrado area. For this, we used high-throughput amplicon sequencing of 16S rRNA genes (metabarcoding) to characterize the bacterial community at different taxonomic levels in a native Cerrado area, in a potato crop area, and in an area with cover crops. Our data indicated significant impacts on soil physicochemical properties and enzymatic activity, which directly reflect the dynamics of bacterial communities. The three bacterial phyla with the highest relative abundance in the three areas were Proteobacteria, Actinobacteriota, and Acidobacteriota. At the taxonomic class level, small variations were observed among areas, while at the amplicon sequence variant (ASV) level, these variations were more pronounced. The alpha diversity indices showed that the bacterial communities among the areas are rich and diverse. Bray-Curtis and Jaccard distance-based PCoA demonstrated an overlap of bacterial communities present in the cover crop area with the native Cerrado area and separation from the potato cultivation area. The in silico prediction demonstrated that the native Cerrado area presented the highest values of functional diversity of the soil bacterial community compared to the others. Thus, our results provide a holistic view of how different land use systems in the Cerrado can influence the taxonomic and functional diversity of soil bacterial communities.

Soil carbon stability regulate carbon dynamics following large-scale afforestation

Large-scale afforestation is considered an effective measure to mitigate climate change. However, due to the differences in the properties of soil organic carbon (SOC), the dynamic response of SOC to large-scale afforestation remained unclear. Therefore, we conducted paired sampling (farmland and afforestation) in plantation areas across northern China to evaluate the relationship between SOC stability and SOC increments (ΔSOC) resulting from afforestation. Our findings indicated that SOC-unstable soil supported greater carbon increments through afforestation, but at the expense of reduced SOC stability after afforestation. Additionally, we observed that this relationship exhibited geographical characteristics, with SOC-unstable soil demonstrating a stronger capacity to enhance ΔSOC at higher latitudes, particularly in the topsoil. This is primarily attributed to the fact that higher latitudes and colder climates enhance the contribution of particulate organic carbon to ΔSOC and weaken the regulatory effect of SOC chemical composition (carboxyl and aromatic carbon) on SOC stability after afforestation. These findings underscore the importance of incorporating pre-afforestation SOC stability to accurately predict soil carbon-afforestation feedback.

Tree carbon allocation to root exudates: implications for carbon budgets, soil sequestration and drought response

Root carbon (C) exudation plays a central role in nutrient acquisition, microbially mediated organic matter decomposition and many other critical ecosystem processes. While it is well known that roots respond strongly to belowground resources, we have a limited quantitative understanding about C allocation to exudates and its fate in soil under changing water availability. This review synthesizes the importance of exudate C fluxes, summarizes studies quantifying mass-specific exudation rate (SER), total exudation rate (TER) and root exudate fraction (REF; the proportion of TER in a plant's C allocation), examines drought effects and highlights key research priorities to advance the understanding of C allocation to exudates in forest ecosystems. On average, SER is often <1 mg C gdry root-1 day-1, TER is 3.8 Pg C year-1 and REF varies between 1 and 17% of net primary production. Spatiotemporal variations in exudation, including seasonal and daily patterns and subsoil exudation, remain critical knowledge gaps. We show that many studies report a 1.2- to 11-fold increase in SER and REF in response to drought. However, TER often remains unchanged, suggesting that absolute exudate C inputs to the soil may stay constant under drought conditions. Disentangling the individual impacts of soil and air drought as well as drought legacy impacts on ecosystem C dynamics are overlooked aspects. By estimating the differences in rhizosphere formation and exudation across various forest biomes, we find that exudate-affected soil volumes are highest in tropical forests and lowest in boreal forests. While current research emphasizes significant C allocation from the canopy to soil via exudates, understanding exudation dynamics and biome-specific responses to drought by using standardized protocols is essential. Expanding these insights is critical for comprehending the role of root exudates in soil organic matter formation, ecosystem resilience and adaptation to climate change.

Soil Microbial Recovery to the Rubber Tree Replanting Process in Ivory Coast

The resistance and resilience of soil microbial communities to an environmental disturbance are poorly documented, due to the lack on onfield diachronic experiments, limiting our ability to design adapted agroecological practices. This is especially true in rubber plantations, one of the most planted tree in tropical areas. We aimed to understand (1) how soil disturbances occurring during the rubber replanting phase affect the soil microbiome, (2) how agricultural practices combining legumes cover crops and tree logging residues shape community resilience and (3) how microbial responses vary across different edaphic contexts. In two plantations with distinct soil properties in Ivory Coast, soil microbial communities were surveyed every 6 months for 24 months after soil perturbation. Community structure, functioning and networks were described based on a 16S/18S rRNA gene investigation. Prokaryotes were generally more resistant to soil perturbation than microeukaryote communities. Prokaryotic resilience dynamics were faster than those of microeukaryotes, the latter being deeply modulated by cover treatments. These specific dynamics were exacerbated in the sandy site. Co-occurrence network modelling provided useful insights into microbial resilience trajectories. We argue that this tool should be more widely used to describe microbial community dynamics. Practices involving a combination of logging residues and legume cover crops have shown beneficial effects on the community resilience in the sandy site and appears as promising agroecological practices. However, the major influence of soil texture warns of the need to consider pedological context when designing pertinent agroecological practices.

Smart Mixture Design Can Steer the Fate of Root-Derived Carbon Into Mineral-Associated and Particulate Organic Matter in Intensively Managed Grasslands

Species choice and richness in intensively managed grassland mixtures regulate soil carbon (C) input via rhizodeposition, with potential consequences for long-term soil organic carbon storage. Based on a field trial with different grass-legume-forb mixtures, we removed roots from the soil, which was then subjected to particle-size fractionation to trace fresh organic carbon (net C rhizodeposition) into particulate organic matter (POM) and mineral-associated organic matter (MAOM). We related these C input fractions to root traits. Using multiple-pulse 13C-CO2-labeling, we captured the net formation of mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) at the end of the growing season. Pure stand perennial ryegrass (Lolium perenne) had higher quantities of rhizodeposited C allocated to MAOC and POC (0.21 and 0.13 g C kg-1 dry soil, respectively) compared to grass-legume-forb mixtures (ranging from 0.10 to 0.12 for MAOC and 0.05 to 0.06 g C kg-1 dry soil for POC). However, the proportion of MAOC (%MAOC of net C rhizodeposition) in relation to that of POC was higher in mixtures with legumes. Species richness did not affect the quantity of MAOC or POC, nor %MAOC. The quantities of MAOC and POC were positively associated with root length. In contrast, %MAOC was positively associated with root diameter and a lower root C:N ratio. Despite higher %MAOC in mixtures with legumes, the main driver of MAOC and POC quantities was the total amount of C rhizodeposition. These results highlight the importance of legumes in the formation of MAOC from rhizodeposition and of high root length for increasing both MAOC and POC quantities. Our study shows how plant community design can be used to increase MAOC and/or POC and facilitate soil C storage. By revealing the traits behind the relationships between plant communities and MAOC and POC formation, we provide a guide for species selection in intensively managed grasslands to mitigate climate change.

Natural forests vs. plantations: A meta-analysis of consequences for soil organic carbon functional fractions

Plantations are becoming more common globally as one of the important initiatives to mitigate global climate change, but the results on whether the soil organic carbon (SOC) can reach the level of natural forests are still inconsistent. Here, we conducted a meta-analysis of 418 paired observations, comparing plantations to adjacent natural forests (primary and secondary forests), from 47 published studies to explore the global patterns and associated drivers of SOC functional fractions (particulate OC, POC; mineral-associated OC, MAOC) and their ratios (the ratio of POC to MAOC, POC:MAOC; the ratio of POC to SOC, POC:SOC; the ratio of MAOC to SOC, MAOC:SOC). We found significant reductions of POC (42.4%, 35.9%), MAOC (19.4%, 15.2%), POC:MAOC (29.0%, 25.5%), and POC:SOC (18.2%, 18.9%) in plantations compared to primary and secondary forests. In contrast, MAOC:SOC in plantations had no change. The effects of plantations on POC, MAOC and their ratios were significantly affected by tree species, plantation age, soil type, and soil depth. Moreover, soil physical properties (soil bulk density, mean weight diameter), element contents (total phosphorus) and microbial communities (microbial biomass C) appeared to be drivers of lower POC, MAOC and their ratios in plantations. Our findings suggest that the reduction of SOC in plantations is mainly distributed in relative labile POC. The results reveal that the SOC functional fractions in plantations developed over time and were comparable to adjacent secondary forests after about 60 years, and plantations with native species will be more conducive to the formation of POC and MAOC. We emphasize that primary forests are not replaceable, and plantations with native species might be a reliable way for restoring a stable distribution of SOC.

Effects of Low-Severity Fire on the Composition and Stability of Soil Organic Carbon in Permafrost Peatlands (Northeast China)

Climate change and human activity are increasing the frequency of wildfires in peatlands and threatening permafrost peatland carbon pools. In Northeast China, low-severity prescribed fires are conducted annually on permafrost peatlands to reduce the risk of wildfires. These fires typically do not burn surface peat but lead to the loss of surface vegetation and introduction of pyrogenic carbon. However, the long-term effects of repeated low-severity fires on soil carbon stability in these ecosystems remain unclear. Thus, we conducted low-severity prescribed fire experiments over 3 years in the permafrost peatlands of the Great Khingan Mountains. Our findings showed a gradual decline in the total carbon content, primarily due to the reduction in free particulate organic matter (fPOM). Initially, fPOM was higher in the burned sites but decreased with repeated burning. Chemical analyses revealed a 32% increase in the aromaticity of the fPOM at the burned sites, which diminished the thermal stability of the soil. Furthermore, both prescribed fires and the addition of pyrogenic carbon reduced biological stability while increasing enzyme activity and CO2 production, which was attributed to the introduction of post-fire pyrogenic carbon. These results suggest that low-severity fires compromise the stability of permafrost peatlands, particularly because the pyrogenic carbon input alters the chemical composition of the soil carbon fraction.

Time and climate roles in driving soil carbon distribution and stability in particulate and mineral-associated organic matter pools

Understanding the accumulation and stability of soil organic matter (SOM) pools as a function of time (i.e., soil age) and climate (i.e., precipitation and temperature) represents a crucial challenge. This study aims at investigating the effect of both climate and time on SOM distribution into particulate and mineral-associated organic matter (POM and MAOM, respectively), using two chronosequences located along a climate gradient. The contribution of POM and MAOM to soil organic carbon (SOC) storage differs between the climo-chronosequences and with depth. The ratio between MAOM and POM pools (MAOM/POM) ranges from 0.9 to 2.0 and from 1.4 to 3.5 in the wetter and cooler and in the drier and warmer chronosequence, respectively. Regardless of the chronosequence, the MAOM/POM ratio increases with depth, highlighting a more important role of the mineral-associated fraction in carbon storage in deeper soils. The concentration of organic carbon in mineral-associated (MAOC) and particulate (POC) pools along the soil profile in the wetter and cooler chronosequence is 2× and 3× higher, respectively, than in soils from the drier and warmer one. In particular, in the wetter and cooler chronosequence, MAOC and POC concentrations decrease with soil age. In the drier and warmer chronosequence, only POC concentration decreases with soil age, whereas MAOC concentration generally increases. The thermal stability of the MAOM fraction increases with soil age and depth only in the drier and warmer climatic conditions, whereas no differences with depth occur in the wetter and cooler chronosequence. Furthermore, the MAOM energy density decreases with soil depth and age in both chronosequences. Independently of the chronosequence, POM represents the most labile pool with higher energy density. In conclusion, time and climate play a different role in SOC distribution between the pools and on their relative stability. Soil age drives MAOM stability in drier and warmer conditions, whereas a wetter and cooler climate determines a higher SOC accumulation in both pools, although these greater carbon stocks are negatively correlated with their stability.

Fungal communities in boreal soils are influenced by land use, agricultural soil management, and depth

Land use and agricultural soil management affect soil fungal communities that ultimately influence soil health. Subsoils harbor nutrient reservoir for plants and can play a significant role in plant growth and soil carbon sequestration. Typically, microbial analyses are restricted to topsoil (0-30 cm) leaving subsoil fungal communities underexplored. To address this knowledge gap, we analyzed fungal communities in the vertical profile of four boreal soil treatments: long-term (24 years) organic and conventional crop rotation, meadow, and forest. Internal transcribed spacer (ITS2) amplicon sequencing revealed soil-layer-specific land use or agricultural soil management effects on fungal communities down to the deepest measured soil layer (40-80 cm). Compared to other treatments, higher proportion of symbiotrophs, saprotrophs, and pathotrophs + plant pathogens were found in forest, meadow and crop rotations, respectively. The proportion of arbuscular mycorrhizal fungi was higher in deeper (>20 cm) soil than in topsoil. Forest soil below 20 cm was dominated by fungal functional groups with proposed interactions with plants or other soil biota, whether symbiotrophic or pathotrophic. Ferrous oxide was an important factor shaping fungal communities throughout the vertical profile of meadow and cropping systems. Our results emphasize the importance of including subsoil in microbial community analyses in differently managed soils.

Tea cultivation: facilitating soil organic carbon accumulation and altering soil bacterial community-Leishan County, Guizhou Province, Southwest China

Background

Camellia sinensis is an important cash crop in southwestern China, with soil organic carbon playing a vital role in soil fertility, and microorganisms contributing significantly to nutrient cycling, thus both of them influencing tea tree growth and development. However, existing studies primarily focus on soil organic carbon, neglecting carbon fractions, and the relationship between soil organic carbon fractions and microbial communities is unclear. Consequently, this study aims to clarify the impact of different tea planting durations on soil organic carbon fractions and microbial communities and identify the main factors influencing microbial communities. It provides a theoretical basis for soil quality evaluation in the study area and scientific guidance for tea plantation management, thus fostering the region's economic sustainability.

Methods

This study selected tea plantations with different tea planting durations of 3-5 years (Y5), 12-16 years (Y15), 18-22 years (Y20), 40-42 years (Y40), and 48-50 years (Y50), as research subjects and adjacent uncultivated forest without a history of tea planting (CK) served as controls. Soil organic carbon (SOC), particulate organic carbon (POC), easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacterial diversity were measured in the 0-20 cm and 20-40 cm soil layers, respectively.

Results

Compared to the adjacent uncultivated forest (CK), the soil organic carbon (SOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), and dissolved organic carbon (DOC) contents in a 40-year tea plantation significantly increased. Nonetheless, the microbial biomass carbon (MBC) content notably decreased. POC/SOC ratios rose with prolonged planting, signifying enhanced conversion of organic carbon into particulate forms. Bacterial community diversity peaked at 15 years and declined by 40 years post-planting and after tea planting dominated by Acidobacteriota, Chloroflexi, Proteobacteria, and Actinobacteriota in the tea garden. FAPROTAX analysis highlighted aerobic and anaerobic chemoheterotrophy, cellulolysis, and nitrogen fixation as key bacterial functions. POC and MBC significantly influenced bacterial community structure. In conclusion, tea plantation soil exhibited the highest organic carbon content at 40 years of tea planting, indicating strong carbon accumulation capacity. However, soil acidification in the tea plantation may affect changes in organic carbon and bacterial community. Therefore, in the tea planting process, it is necessary to improve the management system of tea plantations to ensure the maintenance of a good ecological environment in the tea plantation soil, thus achieving sustainable development of the tea industry in the region.

Soil carbon fractionation as a tool to monitor coastal wetland rehabilitation

Coastal wetland rehabilitation can provide nature-based solutions for climate change mitigation. The high carbon accumulation rate and carbon secured, potentially for several millennia, as soil organic carbon (SOC), is among the reasons. Measuring SOC storage and accrual over time are the main tools to understand rehabilitation success. However, SOC is partitioned among different organic matter fractions with varying physio-chemical properties and stabilities. In this research, we separated different organic matter fractions based on density (free light fraction: f-LF, occluded light fraction: o-LF and heavy fraction: HF) and solubility (dissolved fraction: DF) from soils taken from a wetland under rehabilitation and a pristine mangrove forest in Queensland, Australia. The f-LF and o-LF contain particulate organic carbon (POCf-LF and POCo-LF), whereas HF consists of mineral-associated organic carbon (MAOCHF). Mangroves are superior to wetlands under rehabilitation and terrestrial forests in terms of C storage in each fraction. Soils from both mangroves and wetlands under rehabilitation are dominated by MAOCHF. However, MAOCHF from mangrove soils are relatively physio-chemically stable, while wetlands under rehabilitation are leaching aged-SOC (>1000 years) from the HF to DF as dissolved organic carbon (DOCDF). Therefore, reducing the risk of mobilisation of aged-SOC can be a key to achieve rehabilitation success.

Three-year elevated carbon dioxide concentration does not enhance soil organic carbon quantity due to simultaneously facilitated carbon input and decomposition in a single rice paddy soil evidenced by natural 13C tracing

Soil organic carbon (SOC) markedly contributes to maintaining soil nutrient cycling and mitigating climate change. Elevated carbon (C) dioxide concentration ([CO2]) is widely expected to improve crop yield and increase C storage; however, its effects on rice growth and SOC dynamics remain greatly unclear. Therefore, a three-year (2007-2009) chamber experiment with two [CO2] treatments (380 vs. 680 ppm) was conducted during rice growing seasons. Ultisol soil, taken from a sugarcane (C4 plant) field on Ishigaki island, Okinawa, was used to grow rice (C3 plant). The natural 13C tracing method was utilized to measure the fraction of SOC derived from rice plant, and δ13C values and concentrations of CO2 and CH4 dissolved in soil solutions were determined. Elevated [CO2] significantly increased rice aboveground biomass (AGB) by 11.8 %-28.8 % and assimilated C content by 12.2 %-28.3 %. However, no significant differences were observed in SOC, total nitrogen (N) content, and the C/N ratios between ambient and elevated [CO2]. Elevated [CO2] induced markedly lower δ13C values in both plant and soil samples relative to ambient [CO2]. The annual fractions of plant-derived C input ranged from 5.0 % to 21.2 % in ambient [CO2] and from 5.6 % to 21.9 % in elevated [CO2] without significant differences. Elevated [CO2] stimulated marked increases in dissolved CO2 and CH4 concentrations, and δ13C values of CH4, indicating a positive priming effect of elevated [CO2] on native SOC decomposition for methanogenesis. In conclusion, elevated [CO2] did not affect SOC accumulation by simultaneously increasing C input evidenced by increased AGB, and SOC decomposition as CO2 and CH4 emissions, hence resulting in a stable SOC quantity in rice paddy ecosystems. Our study delves in the nexus between C input and soil C decomposition under elevated CO2 condition, highlighting its significance in prediction of the responses of C storage in paddy ecosystems to future climate change.

Aboveground plants influence heterogeneously soil organic carbon (SOC) and its labile fractions after mixed afforestation: Three afforestation types of Masson's pine in the Upper Yangtze River, China

Mixed forests generally have a higher carbon sequestration potential than pure forests. However, the effects of different types of mixed afforestation on soil organic carbon (SOC) and its labile fractions still remain controversial. We examined the concentrations of each SOC labile fraction at 0-50 cm soil depth, understory plant communities, stand plant biomass and studied their integrated effects on soil carbon stocks in three types of Pinus massoniana afforestation: a monoculture (MPF), a mixed forest with Cunninghamia lanceolata (MCLMF) and a mixed forest with Liquidambar formosana (MLMF). The results showed that the SOC stocks, i.e., concentrations of SOC and its labile fractions, across soil depths in all three afforestation types decreased with soil depth and ranked in the following order: MCLMF > MPF > MLMF. The concentrations of SOC and its labile fractions displayed a significant positive correlation with the diversity and biomass of understory plants and a significant negative correlation with tree biomass. The MCLMF had the largest SOC stocks (83.45 ± 7.59 Mg ha-1) and the smallest aboveground plant biomass carbon stocks (85.2 ± 4.07 Mg ha-1), while those of the MLMF were the opposite (SOC stocks, 35.63 ± 4.47 Mg ha-1; plant biomass carbon stocks, 144.28 ± 1.19 Mg ha-1). The forest carbon stocks (comprising both SOC and plant biomass carbon pools) were ranked as MLMF > MCLMF > MPF. Our results revealed that the diversity and biomass of understory plants can improve the stocks of SOC and its labile fractions, whereas trees may weaken the role of understory plants. In this sense, the diversity and biomass of understory plants should be emphasized in the process of mixed afforestation, especially mixed broadleaf-conifer afforestation, to increase SOC sequestration.

How biochar curbs the negative impacts of plastic mulching on soil enzymes and microorganisms while elevating crop yields in ridge-furrow systems

Ridge-furrow tillage is an important tillage and yield enhancement method used in dry farming areas; however, the spatial characteristics of the soil microenvironment under ridge-furrow tillage and the response of crop yields to mulching and biochar addition are not known. In this study, we conducted a three-year field experiment in which mulch and biochar, alone or combined, were introduced into ridge-furrow tillage system to explore their interactive effects on soil enzyme activities, bacterial communities, functional genes, and crop yields. The findings reveal significant spatial differences in soil physicochemical composition, enzyme activity, microbial communities, and functional genes under ridge-furrow tillage, which are further exacerbated by the addition of mulching and biochar. Under the premise of ridge-furrow tillage, both mulching and biochar addition reduce the α diversity of bacterial communities. Mulching simplifies the bacterial network, while biochar addition has the opposite effect. Mulching and biochar addition increase the relative abundance of carbon, nitrogen, and phosphorus functional genes and accelerate nutrient cycling, especially on the ridges. Mulching significantly improves crop yield but is detrimental to alkaline phosphatase activity and the abundance of the gene function. The addition of biochar mitigates the harm of mulching and further increases alfalfa yield. These findings not only provide scientific support for optimizing ridge-furrow tillage but also deepen our comprehensive understanding of the soil biochemical environment after the addition of mulching and biochar, further revealing their positive effects on yield formation.

Microbial necromass and glycoproteins for determining soil carbon formation under arbuscular mycorrhiza symbiosis

Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil organic carbon (C) dynamics. Whether AMF promote soil C storage and stability is, however, largely unknown. Since microbial necromass C (MNC) and glomalin-related soil protein (GRSP) are stable microbial-derived C in soils, we therefore evaluated how AMF symbiosis alters both soil C pools and their contributions to soil organic C (SOC) under nitrogen fertilization, based on a 16-weeks mesocosm experiment using a mutant tomato with highly reduced AMF symbiosis. Results showed that SOC content is 4.5 % higher following AMF symbiosis. Additionally, the content of MNC and total GRSP were 47.5 % and 22.3 % higher under AMF symbiosis than at AMF absence, respectively. The accumulations of GRSP and microbial necromass in soil were closely associated with mineral-associated organic C and the abundance of AMF. The increased soil living microbial biomass under AMF symbiosis was mainly derived from AMF biomass, and fungal necromass C significantly contributed to SOC accumulation, as evidenced by the higher fungal:bacterial necromass C ratio under AMF symbiosis. On the contrary, bacterial necromass was degraded to compensate for the increased microbial nutrient demand because of the aggravated nutrient limitation under AMF symbiosis, leading to a decrease in bacterial necromass. Redundancy analysis showing that bacterial necromass was negatively correlated with soil C:N ratio supported this argument. Moreover, the relative change rate of total GRSP was consistently greater in nitrogen-limited soil than that of microbial necromass. Our findings suggested GRSP accumulates faster and contributes more to SOC pools under AMF symbiosis than microbial necromass. The positive correlation between the contributions of GRSP and MNC to SOC further provided valuable information in terms of enhancing our understanding of mechanisms underlying the maintenance of SOC stocks through microbial-derived C.

Geographic Distribution Pattern Determines Soil Microbial Community Assembly Process in Acanthopanax senticosus Rhizosphere Soil

The geographic distribution patterns of soil microbial communities associated with cultivated Acanthopanax senticosus plants in Northeast China were investigated. High-throughput sequencing revealed that the diversity and community assembly of bacterial and fungal communities in the inter-root soil varied significantly with geographic location. The study found that bacterial communities were predominantly assembled through stochastic processes at most sites, while fungal communities showed greater variation, with both stochastic and deterministic processes involved. The complexity of bacterial-fungal co-occurrence networks also varied with longitude and latitude, demonstrating both positive and negative interactions. PICRUSt 2.0 and FUNGuild were used to predict the potential functions of soil bacterial and fungal microbiota, respectively, during different land use patterns. The average taxonomic distinctness (AVD) index indicated varying degrees of community stability across sites. Key microbial taxa contributing to community variability were identified through Random Forest modeling, with Bacteriap25 and Sutterellaceae standing out among bacteria, and Archaeorhizomyces and Clavaria among fungi. Soil chemical properties, including pH, TN, TP, EC, and SOC, significantly correlated with microbial diversity, composition, and co-occurrence networks. Structural equation modeling revealed that geographic distribution patterns directly and indirectly influenced soil chemical properties and microbial communities. Overall, the study provides insights into the geographic distribution patterns of soil microbial communities associated with A. senticosus and highlights the need for further research into the underlying mechanisms shaping these patterns.

Dominant Edaphic Controls on Particulate Organic Carbon in Global Soils

The current soil carbon paradigm puts particulate organic carbon (POC) as one of the major components of soil organic carbon worldwide, highlighting its pivotal role in carbon mitigation. In this study, we compiled a global dataset of 3418 data points of POC concentration in soils and applied empirical modeling and machine learning algorithms to investigate the spatial variation in POC concentration and its controls. The global POC concentration in topsoil (0-30 cm) is estimated as 3.02 g C/kg dry soil, exhibiting a declining trend from polar regions to the equator. Boreal forests contain the highest POC concentration, averaging at 4.58 g C/kg dry soil, whereas savannas exhibit the lowest at 1.41 g C/kg dry soil. We developed a global map of soil POC density in soil profiles of 0-30 cm and 0-100 cm with an empirical model. The global stock of POC is 158.15 Pg C for 0-30 cm and 222.75 Pg C for 0-100 cm soil profiles with a substantial spatial variation. Analysis with a machine learning algorithm concluded the predominate controls of edaphic factors (i.e., bulk density and soil C content) on POC concentration across biomes. However, the secondary controls vary among biomes, with solid climate controls in grassland, pasture, and shrubland, while strong vegetation controls in forests. The biome-level estimates and maps of POC density provide a benchmark for modeling C fractions in soils; the various controls on POC suggest incorporating biological and physiochemical mechanisms in soil C models to assess and forecast the soil POC dynamics in response to global change.

Phosphorus dynamics and sustainable agriculture: The role of microbial solubilization and innovations in nutrient management

Phosphorus (P) is an essential element for plant growth, playing a crucial role in various metabolic processes. Despite its importance, phosphorus availability in soils is often restricted due to its tendency to form insoluble complexes, limiting plant uptake. The increasing demand for phosphorus in agriculture, combined with limited global reserves of phosphate rock, has created challenges for sustainable plant production. Additionally, the overuse of chemical phosphorus fertilizers has resulted in environmental degradation, such as eutrophication of water bodies. Increasing agronomic phosphorus (P) efficiency is crucial because of population growth and increased food demand. Hence, microorganisms involved in the P cycle are a promising biotechnological strategy that has gained global interest in recent decades. Microorganisms' solubilization of phosphate rock (PR) is an environmentally sustainable alternative to chemical processing for producing phosphate fertilizers. Phosphorus-solubilizing microorganisms (PSMs), including bacteria and fungi, and their enzymatic processes offer an eco-friendly and sustainable alternative to chemical inputs by converting insoluble phosphorus into forms readily available for plant uptake. Integrating PSMs into agricultural systems presents a promising strategy to reduce dependence on chemical fertilizers, enhance soil health, and contribute to the transition toward more sustainable and resilient agricultural practices. It can be an alternative that reduces the loss of phosphorus in the environment, especially the eutrophication of aquatic systems. This paper explores the challenges of phosphorus availability in agriculture and the potential of microbial phosphorus solubilization as a sustainable alternative to conventional practices.

Microbial trait multifunctionality drives soil organic matter formation potential

Soil microbes are a major source of organic residues that accumulate as soil organic matter, the largest terrestrial reservoir of carbon on Earth. As such, there is growing interest in determining the microbial traits that drive soil organic matter formation and stabilization; however, whether certain microbial traits consistently predict soil organic matter accumulation across different functional pools (e.g., total vs. stable soil organic matter) is unresolved. To address these uncertainties, we incubated individual species of fungi in soil organic matter-free model soils, allowing us to directly relate the physiological, morphological, and biochemical traits of fungi to their soil organic matter formation potentials. We find that the formation of different soil organic matter functional pools is associated with distinct fungal traits, and that 'multifunctional' species with intermediate investment across this key grouping of traits (namely, carbon use efficiency, growth rate, turnover rate, and biomass protein and phenol contents) promote soil organic matter formation, functional complexity, and stability. Our results highlight the limitations of categorical trait-based frameworks that describe binary trade-offs between microbial traits, instead emphasizing the importance of synergies among microbial traits for the formation of functionally complex soil organic matter.

Microbial and mineral interactions decouple litter quality from soil organic matter formation

Current understanding of soil carbon dynamics suggests that plant litter quality and soil mineralogy control the formation of mineral-associated soil organic carbon (SOC). Due to more efficient microbial anabolism, high-quality litter may produce more microbial residues for stabilisation on mineral surfaces. To test these fundamental concepts, we manipulate soil mineralogy using pristine minerals, characterise microbial communities and use stable isotopes to measure decomposition of low- and high-quality litter and mineral stabilisation of litter-C. We find that high-quality litter leads to less (not more) efficient formation of mineral-associated SOC due to soil microbial community shifts which lower carbon use efficiency. Low-quality litter enhances loss of pre-existing SOC resulting in no effect of litter quality on total mineral-associated SOC. However, mineral-associated SOC formation is primarily controlled by soil mineralogy. These findings refute the hypothesis that high-quality plant litters form mineral-associated SOC most efficiently and advance our understanding of how mineralogy and litter-microbial interactions regulate SOC formation.

Degradation-driven vegetation-soil-microbe interactions alter microbial carbon use efficiency in Moso bamboo forests

Microbial carbon utilization efficiency (CUE) is a crucial indicator for evaluating the efficiency of soil carbon sequestration and transformation, which is applied to quantify the proportion of soil carbon extracted by microbes for anabolism (growth) and catabolism (respiration). Previous studies have shown that the degradation of Moso bamboo forests (Phyllostachys edulis) destroyed the aboveground bamboo structure, reduced vegetation carbon storage, and weakened ecosystem carbon sequestration capacity. Interestingly, soil organic carbon stocks are gradually increasing. However, the mechanism by which degradation-induced changes in soil and vegetation characteristics affect microbial CUE and drive soil carbon sequestration remains unclear. Here we selected four stands with the same origin but different degradation years (intensive management, CK; 2 years' degradation, DM1; 6 years' degradation, DM2; and 10 years' degradation, DM3) based on the local management profiles. The principle of space-for-time substitution was used to investigate the changes in microbial CUE along a degradation time and to further identify the controlling biotic and abiotic factors. Our finding showed that microbial CUE increased by 12.27 %, 31.01 %, and 55.95 %, respectively, compared with CK; whereas microbial biomass turnover time decreased from 23.99 ± 1.11 to 17.16 ± 1.20 days. Promoting microbial growth was the main pathway to enhance microbial CUE. Massive inputs of vegetative carbon replenished soil carbon substrate content, and altered microbial communities and life history strategy, which in turn promoted microbial growth and increased microbial CUE. These findings provide theoretical support for the interactions between carbon dynamics and microbial physiology in degraded bamboo forests, and reinforce the importance of vegetation and microbial properties and soil carbon substrates in predicting microbial CUE.

Miscanthus sp. root exudate alters rhizosphere microbial community to drive soil aggregation for heavy metal immobilization

The heavy metals (HMs) spatial distribution in soil is intricately shaped by aggregation processes involving chemical reactions and biological activities, which modulate HMs toxicity, migration, and accumulation. Pioneer plants play a central role in preventing HMs at source, yet the precise mechanisms underlying their involvement in soil aggregation remain unclear. This study investigates HMs distribution within rhizosphere and bulk soil aggregates of Miscanthus sp. grown in tailings to elucidate the impact of root exudates (REs) and rhizosphere microbes. The results indicate that Miscanthus sp. enhance soil stability, increasing the proportion of macroaggregates by 4.06 %-9.78 %. HMs tend to concentrate in coarse-aggregates, particularly within rhizosphere environments, while diminishing in fine-aggregates. Under HMs stress, lipids and lipid-like molecules are the most abundant REs produced by Miscanthus sp., accounting for under up to 26.74 %. These REs form complex with HMs, promoting microaggregates formation. Charged components such as sugars and amino acids further contribute to soil aggregation. REs also regulates rhizosphere bacteria and fungi, with Acidobacteriota, Chloroflexi were the dominant bacterial phyla, while Ascomycota and Basidiomycota dominate the fungal community. The synergistic effect of REs and microorganisms impact soil organic matter and nutrient content, facilitating HMs nanoparticle heteroaggregation and macroaggregates formation. Consequently, soil structure and REs shape the distribution of HMs in soil aggregation. Pioneer plants mediate REs interaction with rhizosphere microbes, promoting the distribution of HMs into macroaggregates, leading to immobilization. This study sheds light on the role of pioneer plants in regulating soil HMs, offering valuable insights for soil remediation strategies.

Contribution of mycorrhizal symbiosis and root strategy to red clover aboveground biomass under nitrogen addition and phosphorus distribution

Soil nutrients exhibit heterogeneity in their spatial distribution, presenting challenges to plant acquisition. Notably, phosphorus (P) heterogeneity is a characteristic feature of soil, necessitating the development of adaptive strategies by plants to cope with this phenomenon. To address this, fully crossed three-factor experiments were conducted using red clover within rhizoboxes. Positions of P in three conditions, included P even distribution (even P), P close distribution (close P), and P far distribution (far P). Concurrently, N addition was two amounts(0 and 20 mg kg- 1), both with and without AMF inoculation. The findings indicated a decrease in aboveground biomass attributable to uneven P distribution, whereas N and AMF demonstrated the potential to affect aboveground biomass. In a structural equation model, AMF primarily increased aboveground biomass by enhancing nodule number and specific leaf area (SLA). In contrast, N addition improved aboveground biomass through increased nodule number or direct effects. Subsequently, a random forest model indicated that under the far P treatment, fine root length emerged as the primary factor affecting aboveground biomass, followed by thickest root length. Conversely, in the even P treatment, the thickest root length was of paramount importance. In summary, when confronted with uneven P distribution, clover plants adopted various root foraging strategies. AMF played a pivotal role in elevating nodule number, and SLA.

Arbuscular mycorrhizal symbiosis enhances the accumulation of plant-derived carbon in soil organic carbon by regulating the biosynthesis of plant biopolymers and soil metabolism

Plant-derived carbon (C) is a critical constituent of particulate organic carbon (POC) and plays an essential role in soil organic carbon (SOC) sequestration. Yet, how arbuscular mycorrhizal fungi (AMF) control the contribution of plant-derived C to SOC storage through two processes (biosynthesis of plant biopolymers and soil metabolism) remains poorly understood. Here, we utilized transcriptome analysis to examine the effects of AMF on P. communis roots. Under the AM symbiosis, root morphological growth and tolerance to stress were strengthened, and the biosynthetic pathways of key plant biopolymers (long-chain fatty acids, cutin, suberin, and lignin) contributing to the plant-derived C were enhanced. In the subsequent metabolic processes, AMF increased soil metabolites contributing to plant-derived C (such as syringic acid) and altered soil metabolic pathways, including carbohydrate metabolism. Additionally, C-acquiring soil extracellular enzyme activities were enhanced by AMF, which could affect the stabilization of plant-derived C in soil. The contents of POC (21.71 g kg-1 soil), MAOC (10.75 g kg-1 soil), and TOC (32.47 g kg-1 soil) in soil were significantly increased by AMF. The concentrations of plant-derived C and microbial-derived C were quantified based on biomarker analysis. AMF enhanced the content of plant-derived C in both POC and MAOC fractions. What's more, plant-derived C presented the highest level in the POC fraction under the AMF treatment. This research broadens our understanding of the mechanism through which plant-derived C contributes to the accumulation of POC and SOC induced by AM symbiosis, and evidences the benefits of AMF application in SOC sequestration.

Organic matter composition and stability in estuarine wetlands depending on soil salinity

Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM (> 70 %) and increased with salinity (70 %-76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 %-81 %) and N (52 %-82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 %-64 %) and N pool (8.6 %-59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.

Soil and stone terraces offset the negative impacts of sloping cultivation on soil microbial diversity and functioning by protecting soil carbon

Cultivation of sloping land is a main cause for soil erosion. Conservation practices, such as soil and stone terraces, may reduce the impacts of erosion but their impacts on soil microbial diversity and functioning related to carbon (C) and nutrient metabolisms remain unclear. This study was conducted to evaluate the effects of slope gradients (5°, 8°, 15°, 25°) and conservation practices (cultivated, uncultivated, soil terrace, and stone terrace) on bacterial and fungal diversities, metagenomic and metabolomic functioning associated with basic soil properties. Our results showed that steep slopes at 25° significantly decreased soil pH, silt percentage, and bacterial and fungal abundances, but that soil and stone terraces increased soil organic C (SOC), silt and clay contents, and fungal abundance compared to sloping cultivated lands. In addition, soil and stone terraces increased both bacterial and fungal alpha diversities, and relative abundances of Crenarchaeota, Nitrospirota, and Latescibacterota, but reduced the proportions of Actinobacteriota and Patescibacteria, thus shifting microbial beta diversities, which were significantly associated with increased SOC and silt content. For metagenomics, soil and stone terraces greatly increased the relative abundance of functional genes related to Respiration, Virulence, disease and defense, Stress response, and nitrogen and potassium metabolisms, such as Denitrification and Potassium homeostasis. For soil metabolomics, a total of 22 soil metabolites was enriched by soil and stone terraces, such as Lipids and lipid-like molecules (Arachidonic acid, Gamma-Linolenic acid, and Pentadecanoic acid), and Organoheterocyclic compounds (Adenine, Laudanosine, Methylpyrazine, and Nicotinic acid). To sum up, soil and stone terraces could reduce some of the negative impacts of steep slope cultivation on soil microbial diversity as well as their metagenomic and metabolomic functioning related to C and nutrient metabolism useful for soil health improvement, potentially bolstering the impact of sustainable practices in erosion hotspots around the world.

Saline-alkali land reclamation boosts topsoil carbon storage by preferentially accumulating plant-derived carbon

Saline-alkali land is an important cultivated land reserve resource for tackling global climate change and ensuring food security, partly because it can store large amounts of carbon (C). However, it is unclear how saline-alkali land reclamation (converting saline-alkali land into cultivated land) affects soil C storage. We collected 189 adjacent pairs of salt-affected and cultivated soil samples (0-30 cm deep) from the Songnen Plain, eastern coastal area, Hetao Plain, and northwestern arid area in China. Various soil properties, the soil inorganic C (SIC), organic C (SOC), particulate organic C (POC), and mineral-associated organic C (MAOC) densities, and plant- and microbial-derived C accumulation were determined. Saline-alkali land reclamation inconsistently affected the SIC density but significantly (P < 0.001) increased the SOC density. The SOC, POC, and MAOC densities were predicted well by the integrative soil amelioration index. Saline-alkali land reclamation significantly increased plant-derived C accumulation and the plant-derived C to microbial-derived C ratios in all saline-alkali areas, and less microbial transformation of plant-derived C (i.e., less lignin degradation or oxidation) occurred in cultivated soils than salt-affected soils. The results indicated that saline-alkali land reclamation leads to plant-derived C becoming the dominant contributor of SOC storage. POC storage and MAOC storage were strongly linked to plant- and microbial-derived C accumulation, respectively, caused by saline-alkali land reclamation. Our findings suggest that saline-alkali land reclamation increases C storage in topsoil by preferentially promoting plant-derived C accumulation.

Advancing forest carbon stocks' mapping using a hierarchical approach with machine learning and satellite imagery

Remote sensing of forests is a powerful tool for monitoring the biodiversity of ecosystems, maintaining general planning, and accounting for resources. Various sensors bring together heterogeneous data, and advanced machine learning methods enable their automatic handling in wide territories. Key forest properties usually under consideration in environmental studies include dominant species, tree age, height, basal area and timber stock. Being proxies of stand productivity, they can be utilized for forest carbon stock estimation to analyze forests' status and proper climate change mitigation measures on a global scale. In this study, we aim to develop an effective machine learning-based pipeline for automatic carbon stock estimation using solely freely available and regularly updated satellite observations. We employed multispectral Sentinel-2 remote sensing data to predict forest structure characteristics and produce their detailed spatial maps. Using the Extreme Gradient Boosting (XGBoost) algorithm in classification and regression settings and management-level inventory data as reference measurements, we achieved quality of predictions of species equal to 0.75 according to the F1-score, and for stand age, height, and basal area, we achieved an accuracy of 0.75, 0.58 and 0.56, respectively, according to the R2. We focused on the growing stock volume as the main proxy to estimate forest carbon stocks on the example of the stem pool. We explored two approaches: a direct approach and a hierarchical approach. The direct approach leverages the remote sensing data to create the target maps, and the hierarchical approach calculates the target forest properties using predicted inventory characteristics and conversion equations. We estimated stem carbon stock based on the same approach: from Earth observation imagery directly and using biomass and conversion factors developed for the northern regions. Thus, our study proposes an end-to-end solution for carbon stock estimations based on the complexation of inventory data at the forest stand level, Earth observation imagery, machine learning predictions and conversion equations for the region. The presented approach enables more robust and accurate large-scale assessments using limited annotated datasets.

Plant Root Secretion Alleviates Carbamate-Induced Molecular Alterations of Dissolved Organic Matter

Studying the interaction between pesticide contamination in the plant system and the dissolved organic matter (DOM) composition is important to understand the impact of pesticides and plants on the ecological function of DOM. The present study investigated the effects of DOM on the bioaccumulation and biotransformation of carbamates in plants, carbamate exposure on DOM composition, and plant root secretion on the interaction between DOM and carbamates. The concentrations of carbamates and their metabolites in living cabbage plants were continuously tracked through an in vivo analytical method. The presence of DOM was found to reduce the highest bioconcentrations and shorten the time it took to reach the highest bioaccumulated amounts of isoprocarb and carbofuran in plants, while it showed no significant effect on the uptake behavior of carbaryl. DOM profiling results indicated that carbamate exposure substantially decreased the number and molecular diversity of DOM. Notably, plant root secretion alleviated carbamate-induced DOM molecular alterations by inducing a higher turnover rate of DOM compared to that in the uncontaminated group, highlighting the role of plants in mitigating the effects of exogenous pesticide exposure on DOM composition and maintaining DOM molecular homeostasis.

Cultivating resilience in wheat: mitigating arsenic toxicity with seaweed extract and Azospirillum brasilense

Arsenic (As) toxicity is a serious hazard to agricultural land due to growing industrialization, which has a negative effect on wheat crop yields. To address this issue, using seaweed extract and Azospirillum brasilense has emerged as an effective strategy for improving yield under stress conditions. However, the combined application of A. brasilense and seaweed extract in wheat crops under As toxicity has not been fully explored. The effectiveness of combining A. brasilense and seaweed extract in reducing As toxicity in wheat production was examined in this study through a 2-year pot experiment with nine treatments. These treatments included a control with no additives and two As concentrations (50 and 70 μM). At 50 and 70 μM, As was tested alone, with seaweed extract, with A. brasilense, and both. Significant results were achieved in reducing As toxicity in wheat crops. Arsenic at 70 μM proved more harmful than at 50 μM. The application of A. brasilense and seaweed extract was more effective in improving crop growth rates, chlorophyll levels, and stomatal conductance. The combined application notably decreased As concentration in wheat plants. It was concluded that applying A. brasilense and seaweed extract not only improves wheat growth but can also improve soil parameters under As toxicity conditions by increasing organic matter contents, boosting nutrient availability, and increasing the production of antioxidant enzymes.

Enhancement of nitrogen on core taxa recruitment by Penicillium oxalicum stimulated microbially-driven soil formation in bauxite residue

Microbially-driven soil formation process is an emerging technology for the ecological rehabilitation of alkaline tailings. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. Herein, a 1-year field-scale experiment was applied to demonstrate the effect of nitrogen input on the structure and function of the microbiome in alkaline bauxite residue. Results showed that the contents of nutrient components were increased with Penicillium oxalicum (P. oxalicum) incorporation, as indicated by the increasing of carbon and nitrogen mineralization and enzyme metabolic efficiency. Specifically, the increasing enzyme metabolic efficiency was associated with nitrogen input, which shaped the microbial nutrient acquisition strategy. Subsequently, we evidenced that P. oxalicum played a significant role in shaping the assemblages of core bacterial taxa and influencing ecological functioning through intra- and cross-kingdom network analysis. Furthermore, a recruitment experiment indicated that nitrogen enhanced the enrichment of core microbiota (Nitrosomonas, Bacillus, Pseudomonas, and Saccharomyces) and may provide benefits to fungal community bio-diversity and microbial network stability. Collectively, these results demonstrated nitrogen-based coexistence patterns among P. oxalicum and microbiome and revealed P. oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. It will aid in promoting soil formation and ecological rehabilitation of bauxite residue. ENVIRONMENT IMPLICATION: Bauxite residue is a highly alkaline solid waste generated during the Bayer process for producing alumina. Attempting to transform bauxite residue into a stable soil-like substrate using low-cost microbial resources is a highly promising engineering. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. In this study, we evidenced the nitrogen-based coexistence patterns among Penicillium oxalicum and microbiome and revealed Penicillium oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. This study can improve the understanding of core microbes' assemblies that affect the microbiome physiological traits in soil formation processes.

Biomolecular budget of persistent, microbial-derived soil organic carbon: The importance of underexplored pools

The details of how soil microorganisms contribute to stable soil organic carbon pools are a pressing knowledge gap with direct implications for soil health and climate mitigation. It is now recognized that microbial necromass contributes substantially to the formation of stable soil carbon. However, the quantification of necromass in soils has largely been limited to model molecules such as aminosugar biomarkers. The abundance and chemical composition of other persistent microbial residues remain unresolved, particularly concerning how these pools may vary with microbial community structure, soil texture, and management practices. Here we use yearlong soil incubation experiments with an isotopic tracer to quantify the composition of persistent residues derived from microbial communities inhabiting sand or silt dominated soil with annual (corn) or perennial (switchgrass) monocultures. Persistent microbial residues were recovered in diverse soil biomolecular pools including metabolites, proteins, lipids, and mineral-associated organic matter (MAOM). The relative abundances of microbial contributions to necromass pools were consistent across cropping systems and soil textures. The greatest residue accumulation was not recovered in MAOM but in the light density fraction of soil debris that persisted after extraction by chemical fractionation using organic solvents. Necromass abundance was positively correlated with microbial biomass abundance and revealed a possible role of cell wall morphology in enhancing microbial carbon persistence; while gram-negative bacteria accounted for the greatest contribution to microbial-derived carbon by mass at one year, residues from gram-positive Actinobacteria and Firmicutes showed greater durability. Together these results offer a quantitative assessment of the relative importance of diverse molecular classes for generating durable soil carbon.

Long-term chemical and organic fertilization induces distinct variations of microbial associations but unanimous elevation of soil multifunctionality

Intricate microbial associations contribute greatly to the multiple functions (multifunctionality) of natural ecosystems. However, the relationship between microbial associations and soil multifunctionality (SMF) in artificial ecosystems, particularly in agricultural ecosystem with frequent fertilization, remains unclear. In this study, based on a 28-year paddy field experiment, high-throughput sequencing and networks analysis was performed to investigate changes in soil microbial (archaea, bacteria, fungi, and protists) associations and how these changes correlate with SMF under long-term fertilization. Compared to no fertilization (CK), both chemical fertilization with N, P, and K (CF) and chemical fertilization plus rice straw retention (CFR) treatments showed significantly higher soil nutrient content, grain yield, microbial abundance, and SMF. With the exception of archaeal diversity, the CF treatment exhibited the lowest bacterial, fungal, and protist diversity, and the simplest microbial co-occurrence network. In contrast, the CFR treatment had the lowest archaeal diversity, but the highest bacterial, fungal, and protist diversity. Moreover, the CFR treatment exhibited the most complex microbial co-occurrence network with the highest number of nodes, edges, and interkingdom edges. These results highlight that both chemical fertilization with and without straw retention caused high ecosystem multifunctionality while changing microbial association oppositely. Furthermore, these results indicate that rice straw retention contributes to the development of the soil microbiome and ensures the sustainability of high-level ecosystem multifunctionality.

Sequestration of Labile Organic Matter by Secondary Fe Minerals from Chemodenitrification: Insight into Mineral Protection Mechanisms

Labile organic matter (OM) immobilized by secondary iron (Fe) minerals from chemodenitrification may be an effective way to immobilize organic carbon (OC). However, the underlying mechanisms of coupled chemodenitrification and OC sequestration are poorly understood. Here, OM immobilization by secondary Fe minerals from chemodenitrification was investigated at different C/Fe ratios. Kinetics of Fe(II) oxidation and nitrite reduction rates decreased with increasing C/Fe ratios. Despite efficient sequestration, the immobilization efficiency of OM by secondary minerals varied with the C/Fe ratios. Higher C/Fe ratios were conducive to the formation of ferrihydrite and lepidocrocite, with defects and nanopores. Three contributions, including inner-core Fe-O and edge- and corner-shared Fe-Fe interactions, constituted the local coordination environment of mineral-organic composites. Microscopic analysis at the molecular scale uncovered that labile OM was more likely to combine with secondary minerals with poor crystallinity to enhance its stability, and OM distributed within nanopores and defects had a higher oxidation state. After chemodenitrification, high molecular weight substances and substances high in unsaturation or O/C ratios including phenols, polycyclic aromatics, and carboxylic compounds exhibited a stronger affinity to Fe minerals in the treatments with lower C/Fe ratios. Collectively, labile OM immobilization can occur during chemodenitrification. The findings on OM sequestration coupled with chemodenitrification have significant implications for understanding the long-term cycling of Fe, C, and N, providing a potential strategy for OM immobilization in anoxic soils and sediments.

Global turnover of soil mineral-associated and particulate organic carbon

Soil organic carbon (SOC) persistence is predominantly governed by mineral protection, consequently, soil mineral-associated (MAOC) and particulate organic carbon (POC) turnovers have different impacts on the vulnerability of SOC to climate change. Here, we generate the global MAOC and POC maps using 8341 observations and then infer the turnover times of MAOC and POC by a data-model integration approach. Global MAOC and POC storages are975 964 987 Pg C (mean with 5% and 95% quantiles) and330 323 337 Pg C, while global mean MAOC and POC turnover times are129 45 383 yr and23 5 82 yr in the top meter, respectively. Climate warming-induced acceleration of MAOC and POC decomposition is greater in subsoil than that in topsoil. Overall, the global atlas of MAOC and POC turnover, together with the global distributions of MAOC and POC stocks, provide a benchmark for Earth system models to diagnose SOC-climate change feedback.

Trade-off between Pore-Throat Structure and Mineral Composition in Modulating the Stability of Soil Organic Carbon

The preservation of soil organic carbon (OC) is an effective way to decelerate the emission of CO2 emission. However, the coregulation of pore structure and mineral composition in OC stabilization remains elusive. We employed the in situ nondestructive oxidation of OC by low-temperature ashing (LTA) combined with near edge X-ray absorption fine structure (NEXAFS), high-resolution microtomography (μ-CT), field emission electron probe microanalysis (FE-EPMA) with C-free embedding, and novel Cosine similarity measurement to investigate the C retention in different aggregate fractions of contrasting soils. Pore structure and minerals contributed equally (ca. 50%) to OC accumulation in macroaggregates, while chemical protection played a leading role in C retention with 53.4%-59.2% of residual C associated with minerals in microaggregates. Phyllosilicates were discovered to be more prominent than Fe (hydr)oxides in C stabilization. The proportion of phyllosilicates-associated C (52.0%-61.9%) was higher than that bound with Fe (hydr)oxides (45.6%-55.3%) in all aggregate fractions tested. This study disentangled quantitatively for the first time a trade-off between physical and chemical protection of OC varying with aggregate size and the different contributions of minerals to OC preservation. Incorporating pore structure and mineral composition into C modeling would optimize the C models and improve the soil C content prediction.

Relationship of selected properties of Cambisols to altitude and forest ecosystems of four vegetation grades

Currently, little is known about the spatial variability of significant soil properties and their relationships to forest ecosystems of different vegetation grades. This work evaluates the variability of the properties of the upper layer of Cambisol taxa and their relationship to altitude and forest ecosystems of 2nd to 5th forest vegetation grades selected in the Western Carpathians using PCA and regression analysis. The content of clay, total carbon and total nitrogen, humus, energy, and ash in the soils varied between 5.43 and 11.53 %, 21-65 mg g-1, 1.9-4.7 mg g-1, 36-112 mg g-1, 438.4-5845.7 J g-1 and 852.9-946.3 mg g-1, and C/N, pHH2O, and pHKCl values ranged between 11.2 and 16.7, 4.0-5.8 and 3.1-4.6. PCA showed that EAC in the 3rd oak-beech vegetation grade had significantly higher pH values and significantly lower energy content, ESC in the 4th beech vegetation grade had a significantly higher ash content and a significantly lower energy content, and DC in the 5th fir-beech vegetation grade had a significantly higher content of Ct, Nt, and humus. Linear regression revealed a strong negative correlation between the energy content and soil reaction (R2 for pHH2O = 0.48; R2 for pHKCl = 0.38) for all Cambisol taxa. Ct content and ash show a strong negative correlation (R2 = 0.78). The positive relationship between altitude and FVGs was found only for the soil Ct (R2 = 0.87), Nt (R2 = 0.81), and humus content (R2 = 0.87). A strong negative linear relationship between altitude and FVGs showed the ash content (R2 = 0.77). In turn, the oscillatory, polynomial course had a relationship between the clay content (R2 = 0.65) and energy (R2 = 0.75) to altitude and FVGs. Recognizing significant soil variables and better understanding their impact on the development of forest ecosystems is a prerequisite for distinguishing areas with the highest risk of their damage under conditions of various anthropogenic interventions and climate change. Therefore, this topic continues to require increased research efforts. For this reason, a better understanding of the relationships between soil properties and ecologically differentiated communities of forest ecosystems will allow us to identify areas with the highest risk of ecological changes that could lead to the degradation of European forests in the future.

Microorganisms Directly Affected Sediment Carbon–Nitrogen Coupling in Two Constructed Wetlands

Clarifying the carbon–nitrogen coupling pattern in wetlands is crucial for understanding the driving mechanism of wetland carbon sequestration. However, the impacts of plants and environmental factors on the coupling of carbon–nitrogen in wetland sediments are still unclear. Sediment samples from plant (Typha angustifolia and Phragmites australis)-covered habitats and bare land were collected in two constructed wetlands in northern China. The contents of different forms of carbon and nitrogen in sediments and plants, and the sediment microbial community were detected. It was found that the sediment carbon to nitrogen (C/N) ratios did not differ significantly in the bare sites of different wetlands, but did in the plant-covered sites, which highlighted the different role of plants in shifting the carbon–nitrogen coupling in different constructed wetlands. The effects of plants on the sediment carbon–nitrogen coupling differed in two constructed wetlands, so the structural equation model was used and found that sediment microorganisms directly affected sediment C/N ratios, while water and sediment physicochemical properties indirectly affected sediment C/N ratios by altering sediment microbial functions. Multiple linear regression models showed that water pH, sediment moisture content, water dissolved oxygen, and water depth had a greater influence on the carbon metabolism potential of the sediment microbial community, while sediment moisture content had the greatest impact on the sediment microbial nitrogen metabolism potential. The study indicates that variations in environmental conditions could alter the influence of plants on the carbon and nitrogen cycles of wetland sediments. Water environmental factors mainly affect microbial carbon metabolism functions, while soil physicochemical factors, especially water content, affect microbial carbon and nitrogen metabolism functions.

Shining a Light on How Soil Organic Carbon Behaves at Fine Scales under Long-Term Elevated CO2: An 8 Year Free-Air Carbon Dioxide Enrichment Study

Building and protecting soil organic carbon (SOC) are critical to agricultural productivity, soil health, and climate change mitigation. We aim to understand how mechanisms at the organo-mineral interfaces influence SOC persistence in three contrasting soils (Luvisol, Vertisol, and Calcisol) under long-term free air CO2 enrichment conditions. A continuous wheat-field pea-canola rotation was maintained. For the first time, we provided evidence to a novel notion that persistent SOC is molecularly simple even under elevated CO2 conditions. We found that the elevated CO2 condition did not change the total SOC content or C forms compared with the soils under ambient CO2 as identified by synchrotron-based soft X-ray analyses. Furthermore, synchrotron-based infrared microspectroscopy confirmed a two-dimensional microscale distribution of similar and less diverse C forms in intact microaggregates under long-term elevated CO2 conditions. Strong correlations between the distribution of C forms and O-H groups of clays can explain the steady state of the total SOC content. However, the correlations between C forms and clay minerals were weakened in the coarse-textured Calcisol under long-term elevated CO2. Our findings suggested that we should emphasize identifying management practices that increase the physical protection of SOC instead of increasing complexity of C. Such information is valuable in developing more accurate C prediction models under elevated CO2 conditions and shift our thinking in developing management practices for maintaining and building SOC for better soil fertility and future environmental sustainability.

Soil's Hidden Power: The Stable Soil Organic Carbon Pool Controls the Burden of Persistent Organic Pollutants in Background Soils

Persistent organic pollutants (POPs) tend to accumulate in cold regions by cold condensation and global distillation. Soil organic matter is the main storage compartment for POPs in terrestrial ecosystems due to deposition and repeated air-surface exchange processes. Here, physicochemical properties and environmental factors were investigated for their role in influencing POPs accumulation in soils of the Tibetan Plateau and Antarctic and Arctic regions. The results showed that the soil burden of most POPs was closely coupled to stable mineral-associated organic carbon (MAOC). Combining the proportion of MAOC and physicochemical properties can explain much of the soil distribution characteristics of the POPs. The background levels of POPs were estimated in conjunction with the global soil database. It led to the proposition that the stable soil carbon pools are key controlling factors affecting the ultimate global distribution of POPs, so that the dynamic cycling of soil carbon acts to counteract the cold-trapping effects. In the future, soil carbon pool composition should be fully considered in a multimedia environmental model of POPs, and the risk of secondary release of POPs in soils under conditions such as climate change can be further assessed with soil organic carbon models.

Remediation of soda-saline-alkali soil through soil amendments: Microbially mediated carbon and nitrogen cycles and remediation mechanisms

Due to the high salt content and pH value, the structure of saline-sodic soil was deteriorated, resulting in decreased soil fertility and inhibited soil element cycling. This, in turn, caused significant negative impacts on crop growth, posing a major challenge to global agriculture and food security. Despite numerous studies aimed at reducing the loss of plant productivity in saline-sodic soils, the knowledge regarding shifts in soil microbial communities and carbon/nitrogen cycling during saline-sodic soil improvement remains incomplete. Consequently, we developed a composite soil amendment to explore its potential to alleviate salt stress and enhance soil quality. Our findings demonstrated that the application of this composite soil amendment effectively enhanced microbial salinity resistance, promotes soil carbon fixation and nitrogen cycling, thereby reducing HCO3- concentration and greenhouse gas emissions while improving physicochemical properties and enzyme activity in the soil. Additionally, the presence of CaSO4 contributed to a decrease in water-soluble Na+ content, resulting in reduced soil ESP and pH by 14.64 % and 7.42, respectively. Our research presents an innovative approach to rehabilitate saline-sodic soil and promote ecological restoration through the perspective of elements cycles.

Soil processes modify the composition of volatile organic compounds (VOCs) from CO2- and CH4-dominated geogenic and landfill gases: A comprehensive study

Degradation mechanisms affecting non-methane volatile organic compounds (VOCs) during gas uprising from different hypogenic sources to the surface were investigated through extensive sampling surveys in areas encompassing a high enthalpy hydrothermal system associated with active volcanism, a CH4-rich sedimentary basin and a municipal waste landfill. For a comprehensive framework, published data from medium-to-high enthalpy hydrothermal systems were also included. The investigated systems were characterised by peculiar VOC suites that reflected the conditions of the genetic environments in which temperature, contents of organic matter, and gas fugacity had a major role. Differences in VOC patterns between source (gas vents and landfill gas) and soil gases indicated VOC transformations in soil. Processes acting in soil preferentially degraded high-molecular weight alkanes with respect to the low-molecular weight ones. Alkenes and cyclics roughly behaved like alkanes. Thiophenes were degraded to a larger extent with respect to alkylated benzenes, which were more reactive than benzene. Furan appeared less degraded than its alkylated homologues. Dimethylsulfoxide was generally favoured with respect to dimethylsulfide. Limonene and camphene were relatively unstable under aerobic conditions, while α-pinene was recalcitrant. O-bearing organic compounds (i.e., aldehydes, esters, ketones, alcohols, organic acids and phenol) acted as intermediate products of the ongoing VOC degradations in soil. No evidence for the degradation of halogenated compounds and benzothiazole was observed. This study pointed out how soil degradation processes reduce hypogenic VOC emissions and the important role played by physicochemical and biological parameters on the effective VOC attenuation capacity of the soil.

Continuous planting of euhalophyte Suaeda salsa enhances microbial diversity and multifunctionality of saline soil

Halophyte-based remediation emerges as a novel strategy for ameliorating saline soils, offering a sustainable alternative to conventional leaching methods. While bioremediation is recognized for its ability to energize soil fertility and structure, the complex interplays among plant traits, soil functions, and soil microbial diversity remain greatly unknown. Here, we conducted a 5-year field experiment involving the continuous cultivation of the annual halophyte Suaeda salsa in saline soils to explore soil microbial diversity and their relationships with plant traits and soil functions. Our findings demonstrate that a decline in soil salinity corresponded with increases in the biomass and seed yield of S. salsa, which sustained a consistent seed oil content of approximately 22% across various salinity levels. Significantly, prolonged cultivation of halophytes substantially augmented soil microbial diversity, particularly from the third year of cultivation. Moreover, we identified positive associations between soil multifunctionality, seed yield, and taxonomic richness within a pivotal microbial network module. Soils enriched with taxa from this module showed enhanced multifunctionality and greater seed yields, correlating with the presence of functional genes implicated in nitrogen fixation and nitrification. Genomic analysis suggests that these taxa have elevated gene copy numbers of crucial functional genes related to nutrient cycling. Overall, our study emphasizes that the continuous cultivation of S. salsa enhances soil microbial diversity and recovers soil multifunctionality, expanding the understanding of plant-soil-microbe feedback in bioremediation.IMPORTANCEThe restoration of saline soils utilizing euhalophytes offers a viable alternative to conventional irrigation techniques for salt abatement and soil quality enhancement. The ongoing cultivation of the annual Suaeda salsa and its associated plant traits, soil microbial diversity, and functionalities are, however, largely underexplored. Our investigation sheds light on these dynamics, revealing that cultivation of S. salsa sustains robust plant productivity while fostering soil microbial diversity and multifunctionality. Notably, the links between enhanced soil multifunctionality, increased seed yield, and network-dependent taxa were found, emphasizing the importance of key microbial taxa linked with functional genes vital to nitrogen fixation and nitrification. These findings introduce a novel understanding of the role of soil microbes in bioremediation and advance our knowledge of the ecological processes that are vital for the rehabilitation of saline environments.

Interplay of soil characteristics and arbuscular mycorrhizal fungi diversity in alpine wetland restoration and carbon stabilization

Alpine wetlands are critical ecosystems for global carbon (C) cycling and climate change mitigation. Ecological restoration projects for alpine grazing wetlands are urgently needed, especially due to their critical role as carbon (C) sinks. However, the fate of the C pool in alpine wetlands after restoration from grazing remains unclear. In this study, soil samples from both grazed and restored wetlands in Zoige (near Hongyuan County, Sichuan Province, China) were collected to analyze soil organic carbon (SOC) fractions, arbuscular mycorrhizal fungi (AMF), soil properties, and plant biomass. Moreover, the Tea Bag Index (TBI) was applied to assess the initial decomposition rate (k) and stabilization factor (S), providing a novel perspective on SOC dynamics. The results of this research revealed that the mineral-associated organic carbon (MAOC) was 1.40 times higher in restored sites compared to grazed sites, although no significant difference in particulate organic carbon (POC) was detected between the two site types. Furthermore, the increased MAOC after restoration exhibited a significant positive correlation with various parameters including S, C and N content, aboveground biomass, WSOC, AMF diversity, and NH4+. This indicates that restoration significantly increases plant primary production, litter turnover, soil characteristics, and AMF diversity, thereby enhancing the C stabilization capacity of alpine wetland soils.

Bacterial community regulation of soil organic matter molecular structure in heavy metal-rich mangrove sediments

Heavy metals (HMs) profoundly impact soil carbon storage potential primarily through soil carbon structure. The association between HM content and soil carbon structure in mangrove sediments remains unclear, likely due to the involvement of microorganisms. In this study, surface sediments in the Futian National Mangrove Nature Reserve were sampled to investigate the chemical structure of soil organic carbon (SOC), the molecular composition of dissolved organic matter (DOM), and potential interactions with microorganisms. HMs, except for Ni, were positively correlated with soil carbon. HMs significantly reduced the alkyl C/O-alkyl C ratio, aromaticity index, and aromatic C values, but increased the labile carboxy/amide C and carbonyl C ratio in SOC. HMs also increased DOM stability, as reflected by the reduced abundance of labile DOM (lipids and proteins) and increased proportion of stable DOM (tannins and condensed aromatics). Bacteria increased the decomposition of labile DOM components (unsaturated hydrocarbons) and the accumulation of stable DOM components (lignins) under HM enrichment. In addition, the association between the bacterial groups and DOM molecules was more robust than that with fungal groups, indicating bacteria had a more significant impact on DOM molecular composition. These findings help in understanding the molecular mechanisms of soil carbon storage in HM-rich mangroves.

Five-year vegetation conversion from pasture to C3 and C4 plants affects dynamics of SOC and TN and their natural stable C and N isotopes via mediating C input and N leaching

Understanding the effects of land-use change on stock and composition of soil organic carbon (SOC) and nitrogen (N) is pivotal for sustainable agriculture and climate change adaption. However, previous studies have often overlooked the specific vegetation type in land-use changes. Therefore, a five-year lysimeter block experiment was conducted, involving non-vegetation, eulalia (C4 plant), and clover (C3 plant) to investigate the impacts of vegetation conversion from pasture on SOC and N dynamics and their natural stable isotopes. Non-vegetation caused 26.21 % and 25.88 % decreases in SOC and total N (TN) contents. Five-year eulalia and clover cultivation maintained stable SOC content, with clover exhibiting higher soil TN content. Eulalia-derived soil C was 1.64-7.58 g C kg-1 and SOC loss in eulalia treatment was 1.86-7.90 g C kg-1. Soil δ13C in eulalia increased at a rate of 0.90 ‰ year-1, significantly surpassing clover and non-vegetation treatments. Conversely, soil δ15N decreased over time, showing insignificant difference among all treatments. Eulalia exhibited significantly higher dry weight and δ13C but lower TN content compared with clover. However, no significant differences were observed in total C and δ15N between the two vegetation treatments. Non-vegetation exhibited higher dissolved organic C concentration than two vegetation treatments in 2017, decreasing over time. Dissolved TN and nitrate concentrations in leachate followed the order clover> non-vegetation> eulalia, with nitrate being the predominant form of N leaching from leachate. Our findings reveal that vegetation conversion affects soil C and N contents, and alters their natural isotopes as well as the leaching of labile soluble nutrients. Notably, non-vegetation consistently reduced SOC and TN contents, whereas eulalia cultivation maintained SOC content, improved C/N ratio and δ13C, and reduced N leaching compared with clover cultivation. These results highlight the potential of eulalia as a candidate plant for enhancing C sequestration and reducing N leaching in cold regions of Japan.