Legume rhizodeposition promotes nitrogen fixation by soil microbiota under crop diversification

Toward Low-Emission Agriculture: Synergistic Contribution of Inorganic Nitrogen and Organic Fertilizers to GHG Emissions and Strategies for Mitigation

Nitrogen (N) and organic-source fertilizers in agriculture are important to sustain crop production for feeding the growing global population. However, their use can result in significant greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which are important climate drivers. This review discusses the interactive effects, uncovering both additive and suppressive outcomes of emissions under various soil and climatic conditions. In addition to examining the effects of nitrogen and the nitrogen use efficiency (NUE), it is crucial to comprehend the mechanisms and contributions of organic fertilizers to GHG emissions. This understanding is vital for developing mitigation strategies that effectively reduce emissions while maintaining agricultural productivity. In this review, the current knowledge is utilized for the management of nitrogen practices, such as the optimization of fertilization rates, timing, and methods of application, in terms of the nitrogen use efficiency and the related GHG emissions. Moreover, we discuss the role of organic fertilizers, including straw, manure, and biochar, as a mitigation strategy in relation to GHG emissions through soil carbon sequestration and enhanced nutrient cycling. Important strategies such as crop rotation, tillage, irrigation, organic fertilizers, and legume crops are considered as suitable approaches for minimizing emissions. Even with the progress made in mitigating fertilizer-related emissions, research gaps remain, specifically concerning the long-term effect of organic fertilizers and the interactions between microbial communities in the soil and fertilization practices. Furthermore, the differences in application practices and environmental conditions present considerable obstacles to accurate emission quantification. This review underlines the importance of conducting more thorough research on the combined application of N and organic fertilizers in multiple cropping systems to evolve region-specific mitigation strategies.

Nitrogen cycle induced by plant growth-promoting rhizobacteria drives "microbial partners" to enhance cadmium phytoremediation

BACKGROUND

Using plant growth-promoting rhizobacteria (PGPR) combined with hyperaccumulator is an ecologically viable way to remediate cadmium (Cd) pollution in agricultural soil. Despite recent advances in elucidating PGPR-enhanced phytoremediation, the response of plant-associated microbiota to PGPR remains unclear.

RESULTS

Here, we found that the effective colonization of PGPR reshaped the rhizosphere nutrient microenvironment, especially driving the nitrogen cycle, primarily mediated by soil nitrate reductase (S-NR). Elevated S-NR activity mobilized amino acid metabolism and synthesis pathways in the rhizosphere, subsequently driving a shift in life history strategies of the rhizosphere microbiota, and enriching specific rare taxa. The reconstructed synthetic community (SynCom3) confirmed that the inclusion of two crucial collaborators (Lysobacter and Microbacterium) could efficiently foster the colonization of PGPR and aid PGPR in executing phytoremediation enhancement. Finally, the multi-omics analysis highlighted the critical roles of phenylpropanoid biosynthesis and tryptophan metabolism pathways in inducing SynCom3 reorganization and PGPR-enhanced phytoremediation.

CONCLUSIONS

Our results underscore the significance of the rhizosphere microenvironment modification by PGPR for its colonization and efficacy, and highlight the collaborative role of rare microbiota in the context of PGPR-enhanced phytoremediation. Video Abstract.

Comparative study of the toxicity responses of Vallisneria natans and Pistia stratiotes to sulfadiazine under different planting methods

Sulfonamides are receiving increased attention due to their persistence in the environment and potential ecological risks. However, there are currently relatively few studies on the toxicity response of aquatic plants grown under the single and mixed planting methods to sulfadiazine (SD). This study investigated the response of the Vallisneria natans (Lour.) Hara (V. natans) and the Pistia stratiotes L. (P. stratiotes) to SD toxicity under single and mixed planting methods. The findings demonstrated that under the mixed planting method, 0.3 μg/L SD significantly reduced the biomass of V. natans (p < 0.05) while increasing the biomass of P. stratiotes. Under the single planting method, the chlorophyll a content of V. natans and P. stratiotes showed the highest value when exposed to 0.3 μg/L SD. The chlorophyll b content of V. natans and P. stratiotes was higher in the single planting method compared to mixed planting method. In single planting, V. natans exhibited the highest superoxide dismutase (SOD) activity when exposed to high concentrations of SD (3.0 μg/L). However, under the mixed planting method, the SOD activity of V. natans and P. stratiotes reduced at 0.3 μg/L SD. P. stratiotes showed increased malondialdehyde (MDA) and glutathione S-transferase (GST) activities at 3.0 μg/L SD under the single planting method. The comprehensive stress resistance ranking was as follows: single planting (V. natans) > mixed planting (P. stratiotes) > mixed planting (V. natans) > single planting (P. stratiotes). Moreover, exposure to SD downregulated the cell motility metabolic pathway of V. natans and P. stratiotes, particularly under the mixed planting method, to increase the resistance of V. natans and P. stratiotes to SD exposure. Proteobacteria, Actinobacteria and Bacteroidetes were the dominant phyla. This study provides basic data and scientific support for the selection of plants for remediation of higher SD polluted waters using ecological remediation.

Rhizospheric crosstalk: A mechanistic overview of how plant secondary metabolites alleviate abiotic stresses

Plants often encounter incompatible growing conditions, such as drought, extreme temperatures, salinity, and heavy metals, which negatively impact their growth and development, resulting in reduced yield and, in severe cases, plant death. These stresses trigger the synthesis of plant secondary metabolites (PSMs), which help plants develop strategies to deter enemies, combat pathogens, outcompete competitors, and overcome environmental restraints. PSMs are released into the rhizosphere and play crucial roles in plant defense and communication. The multifunctionality of PSMs offers new insights into the plant intricate adaptive responses, which can refine our understanding of plant tolerance mechanisms in challenging environments. Thus, elucidating the chemical composition and functions of plant-derived specialized metabolites in the rhizosphere is the key to understanding interactions in this belowground environment. In this review, we aim to elucidate how PSMs exudation shapes the activities and abundance of the rhizosphere microbiome. We also highlight key environmental factors that regulate the structure and diversity of microbial communities. Finally, we discuss various preventive roles of PSMs, exploring how plants recruit microbes preemptively to mitigate diverse abiotic stresses. Additionally, we emphasize the significant contribution of phenolic compounds to the antioxidant defense response in plants, regulated through the shikimate pathway and is considered as a distinctive plant stress resilience component as compared to other PSMs under abiotic stress. Collectively, this study reveals the significance of understanding the multifaceted crosstalk between PSMs and the microbiome, which will facilitate the potential for developing methods to manipulate PSMs-microbiome interaction with predictive outcomes for sustainable crop production.

Small-scale heterogeneity of soil properties in farmland affected fava beans growth through rhizosphere differential metabolites and microorganisms

BACKGROUND

Soil heterogeneity has been acknowledged to influence plant growth, with the small-scale soil heterogeneity always being overlooked in practice. It remains unclear how rhizosphere soil biotics and abiotics respond to soil heterogeneity and how rhizosphere interactions influence crop growth.

RESULTS

In this study, we planted fava beans in a farmland around an e-waste dismantling site, and a distinct boundary (row spacing is 30 cm) was observed in the field during the flowering stage, which divided fava beans phenotypes into two distinct groups (Big vs Little) based on the differences in biomass and height. Soil total concentrations of As, B, Co, Cr, Cu, Pb, Sr, Zn, Ni, Cd and soil pH significantly differed in the rhizosphere of fava beans in the two adjacent rows, which were located on either side of the boundary, with a row-spacing of 30 cm. Random Forest analysis demonstrated that these differentiated soil properties (soil pH, total As, B, Cd, Co, Cr, Cu, Mo, Ni and Zn) substantially influenced fava beans growth (height and biomass). Metagenomic sequencing showed that microbial taxa were significantly enriched their abundance in rhizosphere soils between the two groups of fava beans, with eukaryotic taxa being more sensitively affected. A total of 20 metabolites including coniferyl alcohol, jasmonic acid, resveratrol, and L-aspartic acid, etc. were significantly correlated with fava beans growth. These metabolites were significantly enriched in 15 metabolic pathways (nucleotide metabolism, pyrimidine metabolism, purine metabolism, biosynthesis of plant secondary metabolites, lysine biosynthesis, etc.). Furthermore, 11 microbial genera involved in these metabolic pathways, and these genera were differentially enriched between the two groups and significantly correlated with fava beans growth.

CONCLUSIONS

Overall, the integrated analysis of multi-omics revealed that soil properties heterogeneity at small-scale altered the rhizosphere differential microorganisms and metabolites, which functionally influenced fava beans growth and tolerance to environmental stress. Notably, even soil heterogeneity at such a small spatial scale can cause significant differences in plant growth, and the comprehensive explorations utilizing multi-omics techniques provide novel insights to the field management, which is crucial for the survival and sustainable development of humanity.

The Effect of Climate Variables, Soil Characteristics, and Peanut Cultivars on the Rhizobial Bacteria Community

Peanuts are widely cultivated across the world; however, peanut's rhizobial community and the determinant factors of their composition are still to be elucidated. This study investigates the biogeography and determinant soil environmental factors for peanut rhizobia. A total of 1001 rhizobial isolates were obtained from the peanut root nodules, mainly belonging to two cultivars (X9 and M6) cultivated in 20 sampling sites across China. According to recA sequence analysis, all the isolates were classified as 84 haplotypes, and a representative strain for each haplotype was randomly selected to perform subsequent analyses. Based on multilocus sequence analysis (MLSA) of housekeeping genes dnaK, glnII, gyrB, recA, and rpoB, all the representative strains were classified as 42 genospecies in the genus Bradyrhizobium, including 12 effectively published and 30 undefined genospecies. Strains belonging to six genospecies were predominant (>5%), including B. ottawaense, B. liaoningense, B. yuanmingense, Bradyrhizobium sp. XXIX, B. guangdongense, and B. nanningense. However, only a single isolate was obtained for 15 genospecies. The diversity indices of peanut rhizobia distributed in South China are obviously higher than those in North China, but no obvious peanut cultivar selection for rhizobial genospecies was found. Correlation analyses indicated that the community composition of peanut rhizobia was mainly affected by MAP, MAT, soil AP, and pH. Nodulation tests indicated that the 79 representative strains belonging to 37 genospecies with both nodC and nifH could perform nitrogen-fixing symbiosis with peanuts. This study revealed the great diversity and varied composition of communities of peanut rhizobia in different geographic regions across China.

Towards a Mechanistic Understanding of Legume Functioning in Natural Restoration of Degraded Ecosystem: Legume-Specific Impacts on Nitrogen Transformation Processes

Legumes have important functions in degraded ecosystems as they can mediate atmospheric nitrogen (N) inputs and increase soil N availability. However, it remains unclear whether legumes affect N availability only through biological N fixation or stimulating microbial N transformations. In this study, nine native legumes and four non-legumes were collected following a 9-year natural vegetation restoration experiment in a karst rocky desertification area. Leaf N/phosphorus (P) ratios and various soil N pool compositions were analyzed and gross N transformation rates were determined by 15N tracing techniques. Legumes exhibited higher leaf δ15N values and increased contents of total N, microbial biomass N and inorganic N compared to non‒legumes. Legume leaf N content and N/P ratio (26.7 g kg‒1 and 20.7) significantly exceeded those of non‒legumes (14.2 g kg‒1 and 14.5). Our results indicate that legumes increased soil N availability and decreased plant N limitation after 9 years of natural vegetation succession, with effects varying between species and related to soil N transformation processes. Species with low plant N limitation exhibited high rates of organic N mineralization (MNorg) and ammonium oxidation to nitrate (ONH4), both of which increase inorganic N supply (especially nitrate). This effect was more pronounced in rhizosphere than bulk soil. MNorg and ONH4 rates were positively correlated (p < 0.01) with soil organic carbon, total N, water holding capacity, calcium content and microbial biomass as well as with leaf N:P ratios, indicating legumes improve soil quality and inorganic N supply, thereby alleviating plant N limitation. Our results highlight the importance of legumes in soil N cycling and availability, which is often a limiting factor for natural restoration of degraded ecosystems.

Analysis of soil microbial community structure changes in the drainage field of the Shengli coalfield based on high-throughput sequencing

BACKGROUND

The study of soil environment in drainage fields is important for environmental management and ecological restoration, and there is currently a knowledge gap in understanding the impact of soil microbial communities in the Shengli coalfield drainage fields and the corresponding ecological effects. To investigate the changes in rhizosphere soil microbial communities of different dominant plants after years of restoration, this study examines the improvement effects of different dominant plants on the soil environment.

RESULTS

This study is based on high-throughput sequencing to restore the slope of coal mine spoil after 15 years as the sampling site. The rhizosphere soil of five dominant plants was selected for microbial community analysis, and functional prediction of the microbial community was conducted. The dominant plants selected included Erect Milkvetch (Astragalus adsurgens), Lemongrass (Caragana korshinskii), Alfalfa (Medicago sativa), Phyllanthus pinnatifida (Elymus dahuricus), and Brassica Rapa (Brassica campestris). The results showed that after 15 years of restoration, the soil physicochemical properties in the Phyllanthus pinnatifida group were better than those in the other groups overall, but some of them were inferior to those in the lemon-stripped mallard group. Abundant saprophytic fungal communities were found in different dominant plant groups, mainly belonging to the phyla Ascomycota and Basidiomycota, resulting in significantly higher organic matter content in the dominant plant groups compared to the CK group. The bacterial communities were dominated by the phyla Actinobacteriota, Proteobacteria, Chloroflexi, and Firmicutes. Among these microbial phyla, the Phyllanthus pinnatifida group had higher abundance, which is beneficial for vegetation colonization. Redundancy analysis showed that soil pH was significantly correlated with microbial communities. Organic matter content and pH are the main factors influencing the composition of soil microbial communities, significantly affecting the composition of microorganisms in different groups. After years of restoration, the environment of the Shengli Coalfield's spoil heap has been greatly improved.

CONCLUSIONS

The planting of various beneficial plants has resulted in significant improvements to the soil microbial community and physicochemical properties, with Phyllanthus pinnatifida having the most positive impact. This lays the foundation for the subsequent restoration of the slope of the spoil heap.

Influence of Cover Crop Root Functional Traits on Sweet Potato Yield and Soil Microbial Communities

The symbiotic relationship between cover crops and soil microorganisms is closely linked to nutrient cycling and crop growth within agroecosystems. However, how cover crops with different root functional traits influence soil microbial communities, soil properties, and crop yields has remained understudied. This study assessed the root traits of hairy vetch (HV) and rapeseed (RP), along with soil properties, sweet potato yield, and microbial enzyme activity under red soil dryland conditions. High-throughput sequencing was also employed to characterize the diversity, composition, and network structure of soil bacterial and fungal communities. According to the plant economic spectrum theory and our research results on plant root traits, HV can be identified as a resource-acquisitive cover crop, and RP treatment can be identified as a resource-conservative cover crop. Although RP treatment did not significantly increase the sweet potato yield, the increase rate reached 8.49%. Resource-conservative cover crops were associated with increased pH, SOC, and TP, which enhanced bacterial species diversity and boosted the populations of Chloroflexi and Alphaproteobacteria. In contrast, resource-acquisitive cover crops promoted the proliferation of Gammaproteobacteria. Network analysis indicated that resource-conservative cover crops facilitated network complexity through intensified intra-community competition. Resource-acquisitive cover crops enhanced the stability of microbial communities. Collectively, these findings underscore the distinct advantages of cover crops with varying root functional traits in shaping soil microbial communities. Appropriate cover crop rotations can effectively regulate microbial communities and hold the potential to enhance crop yield.

Introduction of Panax notoginseng into pine forests significantly enhances the diversity, stochastic processes, and network complexity of nitrogen-fixing bacteria in the soil

Introduction

Nitrogen-fixing bacteria (NFB) have a pivotal impact on the nitrogen cycle within agroforestry systems. The organic management of the Panax notoginseng (sanqi)-Pinus armandii agroforestry (SPA) system resulted in nitrogen deficiency because of the lack of application of chemical fertilizers. Therefore, assessing the variability in NFB due to the cultivation of sanqi in the SPA system becomes crucial.

Methods

The seasonal dynamics in the abundance, diversity, and community structure of NFB in the soil of monocropping pine (MP) and SPA systems were assessed using real-time quantitative polymerase chain reaction and high-throughput sequencing technology.

Results and discussion

Sanqi cultivation triggered a decrease in the abundance of NFB but increased α diversity. Additionally, significant differences in the community structure of NFB were noted between the MP and SPA systems. Moreover, the abundance of Bradyrhizobium and Azospirillum increased in the soil after sanqi was cultivated. Furthermore, the cultivation of sanqi broadened the ecological niche breadth of NFB and increased the stochasticity in its community structure assembly (i.e., dispersal limitation). Additionally, the SPA system increased the network complexity but not the stability of NFB. The structural equation model (SEM) revealed that pH directly impacted the network complexity and stability of NFB in the SPA system. Sanqi cultivation positively influences the community characteristics of NFB in the soil in the SPA system. Our study provides new insights into nitrogen cycling and utilization in the SPA system.

Understanding the triacylglycerol-based carbon anabolic differentiation in Cyperus esculentus and Cyperus rotundus developing tubers via transcriptomic and metabolomic approaches

BACKGROUND

Yellow nutsedge (Cyperus esculentus, known as 'YouShaDou' in China, YSD) and purple nutsedge (Cyperus rotundus, known as 'XiangFuZi' in China, XFZ), closely related Cyperaceae species, exhibit significant differences in triacylglycerol (TAG) accumulation within their tubers, a key factor in carbon flux repartitioning that highly impact the total lipid, carbohydrate and protein metabolisms. Previous studies have attempted to elucidate the carbon anabolic discrepancies between these two species, however, a lack of comprehensive genome-wide annotation has hindered a detailed understanding of the underlying molecular mechanisms.

RESULTS

This study utilizes transcriptomic analyses, supported by a comprehensive YSD reference genome, and metabolomic profiling to uncover the mechanisms underlying the major carbon perturbations between the developing tubers of YSD and XFZ germplasms harvested in Yunnan province, China, where the plant biodiveristy is renowned worldwide and may contain more genetic variations relative to their counterparts in other places. Our findings indicate distinct expression patterns of key regulatory genes involved in TAG biosynthesis and lipid droplet formation, including transcriptional factors and structural genes such as ABI3 transcriptional factor, rate-limiting enzymes GPAT3/6/9 and DGAT2/3, and oleosin and caleosin homologs. Furthermore, our omics data suggest that these differences in gene expression are not the sole contributors to the diverse tuber compositions. Instead, complex interactions among highly regulated catalytic reactions, governing carbohydrate, protein, and species-specific metabolite metabolisms, such as starch and sucrose metabolic pathways, flavonoid and amino acids biosynthetic pathways, collectively contribute to the pronounced carbon anabolic differentiation primarily evident in TAG accumulation, as well as the starch properties in mature tubers.

CONCLUSION

This study offers new metabolic insights into the high-value underground non-photosynthetic tissues of Cyperaceae species, which harbors not only high biomass productivity but also abundant nutrients as favorable food or industrial sources in the modern agriculture. The detailed omics analyses aim to deepen our understanding of the Cyperaceae species, which may potentially broaden their application values and facilitate the molecular breeding of better varieties to ameliorate the food safety problem.

Arbuscular mycorrhizal fungi mediate soil N dynamics, mitigating N2O emissions and N-leaching while promoting crop N uptake in green manure systems

Arbuscular mycorrhizal fungi (AMF), as symbionts of the plant root system, play a pivotal ecological role in soil nutrient dynamics. However, the mechanisms by which AMF mediates nitrogen (N) transformation at the soil-crop interface, particularly under green manure management, remain insufficiently understood. This study investigates these mechanisms through a long-term field experiment, employing four green manure management practices during the flowering stage of common vetch: tillage with total green manure incorporation (TG), no-tillage with total green manure mulching (NTG), aboveground biomass removal with root incorporation (T), and aboveground biomass removal with no-tillage (NT), alongside a conventional tillage control without green manure (CT). Results indicate that NTG notably enhanced AMF abundance and dominant species, attributed largely to increases in soil available N, microbial biomass carbon (MBC), and soil pH. AMF colonization rates in maize roots peaked at 69.7 % under NTG. Additionally, soil mineral N was 17.7 % higher under NTG than TG, with aggregate N concentration increasing by 72.4 %. A strong positive correlation emerged between aggregate N and AMF colonization rates. NTG also significantly elevated nos Z gene abundance and nitrous oxide (N2O) reductase activity while lowering the (nir K +nir S) / nos Z ratio. Optimized root architecture under NTG was similarly correlated with AMF colonization, supporting N retention and uptake. Structural equation modeling further confirmed that aggregate N and root structure were primary contributors to reduced N leaching, while root architecture enhanced maize N uptake and N2O reductase activity. The increase in nos Z and N2O reductase reductase significantly reduced N2O emissions. In summary, no-tillage with green manure mulching effectively mitigated N loss and improved crop N uptake by enhancing AMF abundance and colonization.

Dry season irrigation promotes nutrient cycling by reorganizing Eucalyptus rhizosphere microbiome

In southern China, seasonal droughts and low soil phosphorus content constrain the productivity of Eucalyptus trees. To understand the rhizosphere microbiome response to the dry season, metagenomic sequencing analysis was used to investigate the 6-year-old Eucalyptus rhizosphere microbiome under four different irrigation and fertilization treatments. The results showed that irrigation and fertilization during the dry season significantly altered the composition of microbiome in the rhizosphere soil of Eucalyptus plantations. The soil physicochemical properties and enzyme activity explained 30.73 % and 29.75 % of the changes in bacterial and fungal community structure in Eucalyptus rhizosphere soil, respectively. Irrigation and fertilization during the dry season significantly altered the physicochemical properties of rhizosphere soil. Compared with the seasonal drought without fertilizer treatment (CK), the dry season irrigation with fertilizer treatment (WF) significantly increased the content of total nitrogen (46.34 %), available nitrogen (37.72 %), available phosphorus (440.9 %), and organic matter (35.34 %). Soil organic matter (OM), pH, and available phosphorus (AP) were key environmental factors influencing the microbial community composition. Moreover, irrigation and fertilization promoted carbon fixation and nitrogen and phosphorus mineralization, increasing soil OM content and the availability of inorganic nitrogen and phosphorus. Meanwhile, compared to the CK, the increase of acid phosphatase (16.81 %), invertase (146.89 %)and urease (59.45 %) in rhizosphere soil under irrigation (W) treatment further proves that dry season irrigation promote the soil carbon, nitrogen and phosphorus cycles. Irrigation and fertilization treatment alleviated the constraints of low phosphorus in southern China's soil, which promoted Eucalyptus productivity. In conclusion, we suggest implementing reasonable irrigation and fertilization strategies in the production practice of Eucalyptus and utilizing microbial resources to improve soil fertility and Eucalyptus productivity.

Regulation of drought stress on nutrient cycle and metabolism of rhizosphere microorganisms in desert riparian forest

Microbial communities in desert riparian forest ecosystems have developed unique adaptive strategies to thrive in harsh habitats shaped by prolonged exposure to abiotic stressors. However, the influence of drought stress on the functional and metabolic characteristics of soil rhizosphere microorganisms remains unknown. Therefore, this study aimed to investigate the effects of drought stress on soil biogeochemistry and metabolism and analyze the relationship between the biogeochemical cycle processes and network of differentially-expressed metabolites. Using metagenomics and metabolomics, this study explored the microbial functional cycle and differential metabolic pathways within desert riparian forests. The predominant biogeochemical cycles in the study area were the Carbon and Nitrogen cycles, comprising 78.90 % of C, N, Phosphorus, Sulfur and Iron cycles. Drought led to increased soil C fixation, reduced C degradation and methane metabolism, weakened denitrification, and decreased N fixation. Furthermore, drought can disrupt iron homeostasis and reduce its absorption. The differential metabolic pathways of drought stress include flavonoid biosynthesis, arachidonic acid metabolism, steroid hormone biosynthesis, and starch and sucrose degradation. Network analysis of functional genes and metabolism revealed a pronounced competitive relationship between the C cycle and metabolic network, whereas the Fe cycle and metabolic network promoted each other, optimizing resource utilization. Partial least squares analysis revealed that drought hindered the expression and metabolic processes and functional genes, whereas the rhizosphere environment facilitated metabolic expression and the functional genes. The rhizosphere effect primarily promoted metabolic processes indirectly through soil enzyme activities. The integrated multi-omics analysis further revealed that the effects of drought and the rhizosphere play a predominant role in shaping soil functional potential and the accumulation of metabolites. These insights deepen our comprehension of desert riparian forest ecosystems and offer strong support for the functionality of nutrient cycling and metabolite dynamics.

Different responses of individuals, functional groups and plant communities in CSR strategies to nitrogen deposition in high-altitude grasslands

The Competitor, Stress Tolerator, and Ruderal (CSR) theory delineates the ecological strategies of plant species. Nevertheless, how these ecological strategies shift at the levels of individuals, functional groups and plant communities to cope with increasing nitrogen deposition remains unclear. In this study, simulated nitrogen deposition experiments were performed in high-altitude grasslands of alpine meadows and alpine steppe on the Qinghai-Tibetan Plateau (QTP) by employing the strategy and functional type framework (StrateFy) methodology to evaluate plant CSR strategies. Our results indicated that the dominant ecological strategy of the high-altitude grassland on the QTP were predominantly aligned with the R-strategy. In both alpine meadow and alpine steppe grasslands, the community-weighted mean (CWM) of C scores were increased with nitrogen addition, while CWM of R and S scores were not significantly correlated with nitrogen addition. Remarkably, the increase in C scores due to nitrogen enrichment was observed solely in non-legumes, suggesting an enhanced competitive capability of non-legumes in anticipation of future nitrogen deposition. Leymus secalinus was dominated in both alpine meadow and alpine steppe grasslands across all levels of nitrogen deposition, with increasing C scores along the nitrogen gradients. Furthermore, the sensitivity of C scores of individual plant, functional group and plant community to nitrogen deposition rates was more pronounced in alpine steppe grassland than in alpine meadow grassland. These findings furnish novel insights into the alterations of ecological strategies in high-altitude alpine grasslands on the QTP and similar regions worldwide in cope with escalating nitrogen deposition.

Root Endophyte-Manipulated Alteration in Rhizodeposits Stimulates Claroideoglomus in the Rhizosphere to Enhance Drought Resistance in Peanut

Drought dramatically affects plant growth and yield. A previous study indicated that endophytic fungus Phomopsis liquidambaris can improve the drought resistance of peanuts, which is related with the root arbuscular mycorrhizal fungi (AMF) community; however, how root endophytes mediate AMF assembly to affect plant drought resistance remains unclear. Here, we explored the mechanism by which endophytic fungus recruits AMF symbiotic partners via rhizodeposits to improve host drought resistance. The results showed that Ph. liquidambaris enhanced peanut drought resistance by enriching the AMF genus Claroideoglomus of the rhizosphere. Furthermore, metabolomic analysis indicated that Ph. liquidambaris significantly promoted isoformononetin and salicylic acid (SA) synthesis in rhizodeposits, which were correlated with the increase in Claroideoglomus abundance following Ph. liquidambaris inoculation. Coinoculation experiments confirmed that isoformononetin and SA could enrich Claroideoglomus etunicatum in the rhizosphere, thereby improving the drought resistance. This study highlights the crucial role of fungal consortia in plant stress resistance.

Diverse factors influence the amounts of carbon input to soils via rhizodeposition in plants: A review

Rhizodeposition encompasses the intricate processes through which plants generate organic compounds via photosynthesis, store these compounds within aboveground biomass and roots through top-down transport, and subsequently release this organic matter into the soil. Rhizodeposition represents one of the carbon (C) cycle in soils that can achieve long-term organic C sequestration. This function holds significant implications for mitigating the climate change that partly stems from the greenhouse effect associated with increased atmospheric carbon dioxide levels. Therefore, it is essential to further understand how the process of rhizodeposition allocates the photosynthetic C that plants create via photosynthesis. While many studies have explored the basic principles of rhizodeposition, along with the associated impact on soil C storage, there is a palpable absence of comprehensive reviews that summarize the various factors influencing this process. This paper compiles and analyzes the literature on plant rhizodeposition to describe how rhizodeposition influences soil C storage. Moreover, the review summarizes the impacts of soil physicochemical, microbial, and environmental characteristics on plant rhizodeposition and priming effects, and concludes with recommendations for future research.