Soil organic matter dynamics and microbial metabolism along an altitudinal gradient in Highland tropical forests

Dynamic impact of polyethylene terephthalate nanoplastics on antibiotic resistance and microplastics degradation genes in the rhizosphere of Oryza sativa L

This study examined the effects of polyethylene terephthalate (PET) nanoplastics on the rhizosphere of Oryza sativa L., focusing on dynamic changes and interactions among microbial communities, antibiotic resistance genes (ARGs) and microplastic degradation genes (MDGs). PET exposure altered the structure and function of soil microbial, enabling specific microbial groups to thrive in polluted environments. High-dose PET treatments markedly increased the abundance and dissemination of ARGs, primarily via resistance mechanisms such as antibiotic efflux and target alteration. By providing additional carbon sources and surfaces for microbial attachment, PET stimulated the growth of microorganisms harboring MDGs, resulting in an increase in MDGs abundance. The elevated expression of MDGs facilitated the propagation of ARGs, with overlapping host microorganisms suggesting that certain microbial groups exhibit dual metabolic capabilities, enabling them to endure both antibiotic and microplastic pressures. Toxic byproducts of microplastic degradation, such as mono-ethylhexyl phthalate, further promoted ARGs dissemination by increasing horizontal gene transfer frequency. Structural equation modeling revealed that PET indirectly influenced ARGs and MDGs expression by altering soil C/N ratio, available phosphorus, and enzyme activities. Thus, nanoscale PET exacerbates ecological risks to soil microbial communities by driving co-propagation of ARGs and MDGs, highlighting the persistent threat of composite pollution to agroecosystems.

Soil minerals regulate soil organic carbon accumulation through glomalin-related soil protein along an elevation gradient in a mountain arid ecosystem

Soil minerals and glomalin-related soil protein (GRSP), as key soil binding agents, play a crucial role in enhancing soil organic carbon (SOC) sequestration. However, the key driving mechanisms of SOC accumulation process mediated by soil minerals and GRSP remain poorly understood in the arid elevation gradients. This study aimed to evaluate how soil minerals and GRSP affect SOC accumulation across an elevation gradient ranging from 1707 to 3548 m a.s.l on the northern slope of the Central Kunlun Mountains. We collected soil samples from two depths (0-10 cm and 10-30 cm) across the elevation gradient. Bulk soil organic carbon (OC), aggregate-associated OC content, Al/Fe oxides, Ca2+, and GRSP all increased along the elevational gradient at both soil depths of 0-10 cm and 10-30 cm. Specifically, microaggregate OC constituted the larger proportion and played a crucial role in promoting SOC accumulation. Random forest analysis revealed that soil minerals (41.63-60.75%) were the dominant factors driving SOC accumulation. Partial least squares path modelling revealed that SOC accumulation was directly influenced by GRSP, climate, and elevation; indirectly influenced by soil minerals and physiochemical factors. Soil minerals regulated SOC accumulation primarily through GRSP. Overall, the contribution of soil minerals to SOC accumulation processes in mountain ecosystems was considerably greater than that of climate and vegetation. These findings highlight the critical of soil minerals and GRSP factors in regulating SOC accumulation in arid mountain ecosystem, providing valuable insights for climate change mitigation strategies.

Variation in dissolved organic matter characteristics of soil aggregates in slip deposition zone with natural succession on a semiarid region

Variations in soil properties of soil slips during vegetation restoration have been tentatively explored. This study explores the impact of successional age in soil slip deposition zones (depth <3 m) on the dissolved organic matter (DOM) characteristics of soil aggregates across different sizes and soil layers. The variation in DOM properties with successional age, soil depth, and aggregate size was examined using UV-visible and excited emission matrix spectral techniques. Overall, dissolved organic carbon (DOC) content in soil aggregates with three sizes increased with successional age, particularly in aggregates larger than 2 mm. The DOC content of soil aggregates was greater in top soil layer (TSL) (0-2 cm) (303.04 mg kg-1) and middle soil layer (MSL) (2-20 cm) (217.81 mg kg-1) than in the bottom soil layer (BSL) (20-50 cm) (75.81 mg kg-1). The molecular weight and aromaticity of soil DOM were gradually increased with the successional age. Parallel factor analysis revealed a gradual increase in humic-like components and a decrease in protein-like components with the successional age. Notable layer differences were observed, with higher humic-like components in TSL (31 %) and MSL (32 %) compared to the BSL (28 %). Particularly, DOM in the TSL and MSL was primarily controlled by plant sources, whereas it was mainly affected by microbial sources for the DOM in the BSL. In this case, the autochthonous characteristics of soil aggregates in the TSL increased and after that decreased with successional age, while vice versa for the MSL and BSL.

High-elevation-induced decrease in soil pH weakens ecosystem multifunctionality by influencing soil microbiomes

Plant environmental stress response has become a global research hotspot, yet there is a lack of clear understanding regarding the mechanisms that maintain microbial diversity and their ecosystem services under environmental stress. In our research, we examined the effects of moderate elevation on the rhizosphere soil characteristics, microbial community composition, and ecosystem multifunctionality (EMF) within agricultural systems. Our findings revealed a notable negative correlation between EMF and elevation, indicating a decline in multifunctionality at higher elevations. Additionally, our analysis across bacterial and protistan communities showed a general decrease in microbial richness with increasing elevation. Using random forest models, pH was identified as the key environmental stressor influencing microbial communities. Furthermore, we found that microbial community diversity is negatively correlated with stability by mediating complexity. Interestingly, while pH was found to affect the complexity within bacterial networks, it did not significantly impact the ecosystem stability along the elevation gradients. Using a Binary-State Speciation and Extinction (BiSSE) model to explore the evolutionary dynamics, we found that Generalists had higher speciation rates and lower extinction rates compared to specialists, resulting in a skewed distribution towards higher net diversification for generalists under increasing environmental stress. Moreover, structural equation modeling (SEM) analysis highlighted a negative correlation between environmental stress and community diversity, but showed a positive correlation between environmental stress and degree of cooperation & competition. These interactions under environmental stress indirectly increased community stability and decreased multifunctionality. Our comprehensive study offers valuable insights into the intricate relationship among environmental factors, microbial communities, and ecosystem functions, especially in the context of varying elevation gradients. These findings contribute significantly to our understanding of how environmental stressors affect microbial diversity and ecosystem services, providing a foundation for future ecological research and management strategies in similar contexts.

A study of microbial diversity in a biofertilizer consortium

Biofertilizers supply living microorganisms to help plants grow and keep their health. This study examines the microbiome composition of a commercial biofertilizer known for its plant growth-promoting activity. Using ITS and 16S rRNA gene sequence analyses, we describe the microbial communities of a biofertilizer, with 163 fungal species and 485 bacterial genera found. The biofertilizer contains a variety of microorganisms previously reported to enhance nutrient uptake, phytohormone production, stress tolerance, and pathogen resistance in plants. Plant roots created a microenvironment that boosted bacterial diversity but filtered fungal communities. Notably, preserving the fungal-inoculated substrate proves critical for keeping fungal diversity in the root fraction. We described that bacteria were more diverse in the rhizosphere than in the substrate. In contrast, root-associated fungi were less diverse than the substrate ones. We propose using plant roots as bioreactors to sustain dynamic environments that promote the proliferation of microorganisms with biofertilizer potential. The study suggests that bacteria grow close to plant roots, while root-associated fungi may be a subset of the substrate fungi. These findings show that the composition of the biofertilizer may be influenced by the selection of microorganisms associated with plant roots, which could have implications for the effectiveness of the biofertilizer in promoting plant growth. In conclusion, our study sheds light on the intricate interplay between plant roots and the biofertilizer's microbial communities. Understanding this relationship can aid in optimizing biofertilizer production and application, contributing to sustainable agricultural practices and improved crop yields.

Impacts of anthropogenic climate change on tropical montane forests: an appraisal of the evidence

In spite of their small global area and restricted distributions, tropical montane forests (TMFs) are biodiversity hotspots and important ecosystem services providers, but are also highly vulnerable to climate change. To protect and preserve these ecosystems better, it is crucial to inform the design and implementation of conservation policies with the best available scientific evidence, and to identify knowledge gaps and future research needs. We conducted a systematic review and an appraisal of evidence quality to assess the impacts of climate change on TMFs. We identified several skews and shortcomings. Experimental study designs with controls and long-term (≥10 years) data sets provide the most reliable evidence, but were rare and gave an incomplete understanding of climate change impacts on TMFs. Most studies were based on predictive modelling approaches, short-term (<10 years) and cross-sectional study designs. Although these methods provide moderate to circumstantial evidence, they can advance our understanding on climate change effects. Current evidence suggests that increasing temperatures and rising cloud levels have caused distributional shifts (mainly upslope) of montane biota, leading to alterations in biodiversity and ecological functions. Neotropical TMFs were the best studied, thus the knowledge derived there can serve as a proxy for climate change responses in under-studied regions elsewhere. Most studies focused on vascular plants, birds, amphibians and insects, with other taxonomic groups poorly represented. Most ecological studies were conducted at species or community levels, with a marked paucity of genetic studies, limiting understanding of the adaptive capacity of TMF biota. We thus highlight the long-term need to widen the methodological, thematic and geographical scope of studies on TMFs under climate change to address these uncertainties. In the short term, however, in-depth research in well-studied regions and advances in computer modelling approaches offer the most reliable sources of information for expeditious conservation action for these threatened forests.

Soil enzyme activity and stoichiometry in secondary grasslands along a climatic gradient of subtropical China

Soil extracellular enzymes plays key roles in ecosystem carbon (C), nitrogen (N), and phosphorus (P) cycling, and are very sensitive to climatic, plant, and edaphic factors. However, the interactive effects of these factors on soil enzyme activities at large spatial scales remain unclear. Here, we investigated the spatial pattern of the activities of five soil hydrolyzing enzymes [β-D-cellobiohydrolase (CB), β-1,4-glucosidase (BG), β-1,4-N-acetyl-glucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (AP)], and their C:N:P acquisition ratios in relation to plant inputs and edaphic properties across a 600-km climatic gradient in secondary grasslands of subtropical China. The activities of CB, BG, and NAG decreased while that of LAP increased with the increasing mean annual temperature (MAT). The activities of all enzymes did not significantly vary with the mean annual precipitation (MAP). We found that the activities of BG, NAG, and AP were predominately dependent on plant N contents, while the soil LAP activity was tightly related to soil recalcitrant C and N contents. In contrast, the ecoenzymatic C:nutrient (N and P) acquisition ratios increased with increasing MAP and decreasing MAT, primarily due to the increase in plant input at warmer and wetter sites. In addition to climates, plant C inputs, C use efficiency, soil pH, soil organic C, soil C:P, and N:P ratios explained 79% and 72% of the overall variation in ecoenzymatic C:nutrient and P:N acquisition ratios, respectively. The pattern of ecoenzymatic C:N:P acquisition ratios also revealed unexpected N limitation in subtropical grasslands. Overall, our study highlighted the importance of climate in controlling soil biological C, N, and P acquisition activities through its direct and indirect effects on plant inputs and soil edaphic factors, thereby providing useful information for better understanding and predictions of soil C and nutrient cycling in grassland ecosystems at regional scales.

Effect of high soil C/N ratio and nitrogen limitation caused by the long-term combined organic-inorganic fertilization on the soil microbial community structure and its dominated SOC decomposition

The application of organic fertilizers, such as straw and manure, is an efficient approach to maintain soil productivity. However, the effect of these organic fertilizers on soil microbial nutrient balance has not yet been established. In this study, the effects of the long-term combined organic-inorganic fertilization on microbial community were investigated by conducting a 30-year-long field test. Overall, the following five fertilizer groups were employed: inorganic NP fertilizer (NP), inorganic NK fertilizer (NK), inorganic NPK fertilizer (NPK), NPK + manure (MNPK), and NPK + straw (SNPK). The results indicated that the mean natural logarithm of the soil C:N:P acquisition enzyme ratio was 1.04:1.11:1.00 under organic-inorganic treatments, which showed a deviation from its overall mean ratio of 1:1:1. This indicates that microbial resources do not have a balance. Vector analysis (vector angle <45°) and threshold elemental ratio analysis (R_C:N-TER_C:N > 0) further demonstrated that the microbial metabolism was limited by Nitrogen (N) under SNPK and MNPK treatments. N limitation further influenced soil microbial community structure and its dominated SOC decomposition. Specifically, Microbial communities transformed into a more oligotrophic-dominant condition (fungal, Acidobacteria, Chloroflexi) from copiotrophic-dominant (Proteobacteria, Actinobacteria) condition with increasing N limitation. Lysobacter genus and Blastocatellaceae family, in the bacterial communities along with the Mortierella elongata species in fungal communities, were markedly associated with the N limitation, which could be the critical biomarker that represented N limitation. Both correlation analysis and partial least squares path modeling showed significant positive effects of N limitation on the ratio of bacterial functional genes (Cellulase/Amylase), involved in recalcitrant SOC degradation.

Effects of Land Use Change from Natural Forest to Livestock on Soil C, N and P Dynamics along a Rainfall Gradient in Mexico

The effects of converting native forests to livestock systems on soil C, N and P contents across various climatic zones are not well understood for the tropical region. The goal of this study was to test how soil C, N and P dynamics are affected by the land-use change from natural forests to livestock production systems (extensive pasture and intensive silvopastoral systems) across a rainfall gradient of 1611–711 mm per year in the Mexican tropics. A total of 15 soil-based biogeochemical metrics were measured in samples collected during the dry and rainy seasons in livestock systems and mature forests for land-use and intersite comparisons of the nutrient status. Our results show that land-use change from natural forests to livestock production systems had a negative effect on soil C, N and P contents. In general, soil basal respiration and C-acquiring enzyme activities increased under livestock production systems. Additionally, reduction in mean annual rainfall affected moisture-sensitive biogeochemical processes affecting the C, N and P dynamics. Our findings imply that land-use changes alter soil C, N and P dynamics and contents, with potential negative consequences for the sustainability of livestock production systems in the tropical regions of Mexico investigated.