Soil Microbial Nutrient Research Articles

Rubber-Based Agroforestry Ecosystems Enhance Soil Enzyme Activity but Exacerbate Microbial Nutrient Limitations

Agroforestry ecosystems are an efficient strategy for enhancing soil nutrient conditions and sustainable agricultural development. Soil extracellular enzymes (EEAs) are important drivers of biogeochemical processes. However, changes in EEAs and chemometrics in rubber-based agroforestry systems and their mechanisms of action are still not fully understood. Distribution of EEAs, enzymatic stoichiometry, and microbial nutrient limitation characteristics of rubber plantations under seven planting patterns (RM, rubber monoculture system; AOM, Hevea brasiliensis-Alpinia oxyphylla Miq; PAR, Hevea brasiliensis-Pandanus amaryllifolius Roxb; AKH, Hevea brasiliensis-Alpinia katsumadai Hayata; CAA, Hevea brasiliensis-Coffea Arabica; CCA, Hevea brasiliensis-Cinnamomum cassia (L.) D. Don, and TCA, Hevea brasiliensis-Theobroma Cacao) were analyzed to investigate the metabolic limitations of microorganisms and to identify the primary determinants that restrict nutrient limitation. Compared with rubber monoculture systems, agroforestry ecosystems show increased carbon (C)-acquiring enzyme (EEAC), nitrogen (N)-acquiring enzyme (EEAN), and phosphorus (P)-acquiring enzyme (EEAP) activities. The ecoenzymatic stoichiometry model demonstrated that all seven plantation patterns experienced C and N limitation. Compared to the rubber monoculture system, all agroforestry systems exacerbated the microbial limitations of C and N by reducing the vector angle and increasing vector length. P limitation was not detected in any plantation pattern. In agroforestry systems, progression from herbs to shrubs to trees through intercropping results in a reduction in soil microbial nutrient constraints. This is primarily because of the accumulation of litter and root biomass in tree-based systems, which enhances the soil nutrient content (e.g., soil organic carbon, total nitrogen, total phosphorus, and ammonium nitrogen) and accessibility. Conversely, as soil depth increased, microbial nutrient limitations tended to become more pronounced. Partial least squares path modelling (PLS-PM) indicated that nutrient ratios and soil total nutrient content were the most important factors influencing microbial C limitation (−0.46 and 0.40) and N limitation (−0.30 and −0.42). This study presented novel evidence regarding the constraints and drivers of soil microbial metabolism in rubber agroforestry systems. Considering the constraints of soil nutrients and microbial metabolism, intercropping of rubber trees with arboreal species is recommended over that of herbaceous species to better suit the soil environment of rubber plantation areas on Hainan Island.

Ecosystem compartment stoichiometry drives the secondary succession processes of zokor‐disturbed grassland

AbstractIn terrestrial ecosystems, resource availability and soil microbial biomass are substantially changed with ecological recovery. However, the shifts in resource stoichiometry and microbial biomass stoichiometry often do not align, leading to stoichiometric imbalance that constrains microbial growth and, consequently, affects plant community succession. The mechanisms by which soil microbes acclimate to these imbalances and how such adjustments influence plant community dynamics remain largely unexplored in alpine grasslands. To address these processes, we examined ecological stoichiometry during the secondary succession of zokor‐disturbed grassland on the Qinghai–Tibet Plateau, China, utilizing a space‐for‐time substitution approach. Carbon (C), nitrogen (N) and phosphorus (P) contents across plant–soil–microbe and soil ecoenzymatic activities involved in soil microbial nutrient acquisition were measured. The results indicated that C:P and N:P imbalances between microbes and their plant resources intensified with the recovery of zokor‐disturbed grassland. This led to phosphorus limitation in microbial growth, as indicated by the mean vector angles exceeding 45° and decreased threshold element ratio of C:P. In response, soil microbes increased their production of P‐acquiring enzymes to mitigate P limitation. Through structural equation modelling (SEM), we found that the C:N:P ratios within the plant–soil–microbe systems explained 74.5% of the total variance in plant aboveground biomass. We concluded that maintaining balanced C:N:P stoichiometric ratios in plant–soil–microbe systems, facilitated by soil ecoenzymatic activities, enhances plant diversity and net primary productivity during the recovery of zokor‐disturbed grassland.

Vegetation drives soil microbial metabolic limitation through modifications of soil properties and microbial biomass during desert grassland-shrubland state anthropogenic transition

Shrub encroachment became widespread in grass-dominated ecosystem regions. However, there is still limited attention on the changes in plant-soil system C:N:P stoichiometry and soil microbial metabolic limitation status caused by anthropogenic encroachment of shrubs in the desert grassland of northwest China, as well as their driving mechanisms. In this study, we quantified the C:N:P stoichiometry of plant-litter-soil, soil physicochemical properties, microbial biomass, extracellular enzyme activities, and microbial metabolic limitation status during the anthropogenic transition from grassland to shrubland. Here, our results showed that anthropogenic shrub encroachment reduced plant C, soil water, and soil nutrient contents while increasing N and P contents in both plants and litter. The correlation also suggested that litter nutrient content relied on plant nutrients, while plants depleted soil nutrients. Secondly, with the gradient of shrub encroachment, the stoichiometry (except for soil C:N ratio) of plant-litter-soil showed a decreasing trend and a positive correlation. Furthermore, our study indicated that shrub encroachment reduced soil microbial biomass and extracellular enzyme activities, altering microbial stoichiometry and patterns of enzyme allocation. Redundancy analysis revealed that microbial biomass, extracellular enzyme activities, and stoichiometry were mainly driven by soil water content, nutrient content, and nutrient stoichiometry. The vector-threshold element ratio model revealed that along the transition from desert grassland to shrubland, soil microbial nutrient limitation shifted from P to N, while energy (C) limitation intensified. The soil microbial metabolic limitation was driven jointly by plants and litter through modifications of soil properties and microbial biomass. Additionally, soil properties played a crucial role among these factors. In summary, over the past 40 years, shrub anthropogenic encroachment has formed a desert grassland-shrub mosaic landscape, depleted soil water and nutrient contents, and altered ecological stoichiometry and microbial metabolic limitation patterns in northwest China. This study provides new insights into the C, N, and P cycling in plant-soil systems following shrub encroachment caused by global climate change and anthropogenic disturbances.

Mechanisms of litter input changes on soil organic carbon dynamics: a microbial carbon use efficiency-based perspective

Plant litter is an important source of soil organic carbon (SOC) in terrestrial ecosystems, and the pattern of litter inputs is also influenced by global change and human activities. However, the current understanding of the impact of changes in litter inputs on SOC dynamics remains contentious, and the mechanisms by which changes in litter inputs affect SOC have rarely been investigated from the perspective of microbial carbon use efficiency (CUE). We conducted a 1-year experiment with litter treatments (no aboveground litter (NL), natural aboveground litter (CK), and double aboveground litter (DL)) in Robinia pseudoacacia plantation forest on the Loess Plateau. The objective was to assess how changes in litter input affect SOC accumulation in forest soils from the perspective of microbial CUE. Results showed that NL increased soil microbial C limitation by 77.11 % (0–10 cm) compared to CK, while it had a negligible effect on nitrogen and phosphorus limitation. In contrast, DL had no significant effect on soil microbial nutrient limitation. Furthermore, NL was found to significantly increase microbial CUE and decrease microbial metabolic quotient (QCO2), while the opposite was observed with DL. It is noteworthy that NL significantly contributed to an increase in SOC of 30.72 %, while DL had no significant effect on SOC. Correlation analysis showed that CUE was directly proportional to SOC and inversely proportional to QCO2. The partial least squares pathway model indicated that NL indirectly regulated the accumulation of SOC, mainly through two pathways: promoting microbial CUE increase and reducing QCO2. Overall, this study elucidates the mechanism and novel insights regarding SOC accumulation under changes in litter input from the perspective of microbial CUE. These findings are critical for further comprehension of soil carbon dynamics and the terrestrial C-cycle.

Long-term agricultural cultivation decreases microbial nutrient limitation in coastal saline soils

Soil enzyme activities are pivotal for diverse biochemical processes and are sensitive to land use changes. They can indicate soil microbial nutrient limitations. Nonetheless, the mechanism governing the response of soil microbial nutrient limitation to land use alterations in coastal regions remains elusive. We assessed soil nutrients, microbial biomass, and extracellular enzyme activities across various land use types—natural (wasteland and woodland) and agricultural (farmland and orchard)—in the Hangzhou Bay area, China. All four land use types experience co-limitation by carbon (C) and phosphorus (P). However, the extent of microbial resource limitations varies among them. Long-term agricultural practices diminish microbial C and P limitations in farmland and orchard soils compared to natural soils, as evidenced by lower ecoenzymatic C:N ratios and vector lengths, alongside higher microbial carbon use efficiency (CUE). Soil nutrient stoichiometric ratios and CUE are primary factors influencing microbial C and P limitations. Thus, fostering appropriate land use and management practices proves imperative to regulate soil nutrient cycles and foster the sustainable management of coastal areas.

Drought stress impacts soil microbial nutrient limitation more strongly than O3 pollution

Summer drought conditions generally coincide with exposure to high ground-level concentrations of ozone (O3). These two stressors compromise the availability of water, energy, and nutrients to vegetation and microbial communities present within the soil. However, relatively little is known regarding the responses of rhizosphere and non-rhizosphere soil microbial nutrient acquisition to conditions of drought and O3 exposure. Here, we used ecoenzymatic stoichiometry modeling and vector analyses to decipher the resource constraints on rhizosphere and non-rhizosphere soil microbial metabolic limitation within the soil of hybrid poplars exposed to two watering regimens (well-watered or reduced water of 40 %) and two chronic O3 treatments (charcoal-filtered air or ambient air +40 ppb of O3). Results show that, simulated drought stress resulted in stronger effects on the structure of soil microbial communities and associated enzymatic activity relative to exposure to elevated O3 levels. Exposure to these two stressors induced a microbial phosphorus (P) limitation response, with these limitation effects being more pronounced in the rhizosphere soil relative to non-rhizosphere soil. Structural equation modeling revealed that drought-associated declines in soil water availability and pH values were the primary factors influencing this microbial P limitation. Reduced soil water levels resulted in the exacerbation of microbial P limitation as a consequence of the inhibition of P mineralization and availability of C and N, whereas declining soil pH values had the opposite effect, alleviating microbial P limitations by reducing soil alkalinity and thereby aiding in the dissolution of the insoluble P present in alkaline soil. These results emphasize the complex responses of rhizosphere and non-rhizosphere soil microbial metabolic activity to elevated O3 levels and drought stress, providing invaluable insight into the importance of elemental stoichiometry-driven microbial metabolic variability of nutrient cycling activity at the root-soil interface in O3-polluted and drought-exposed ecosystems.

Regional-scale biogeographical patterns of soil extracellular enzyme activities across eight Chinese fir plantation locations

Chinese fir (Cunninghamia lanceolata) is the most important conifer tree species in plantations in subtropical China. Soil extracellular enzyme activities (EEAs) play key roles in mediating multiple forest ecosystem functions, such as organic matter decomposition, nutrient cycling, and plant productivity. In this study, the activities of five soil extracellular enzymes and their stoichiometric (EES) features were investigated at eight Chinese fir plantation locations. The results showed that the soil EEAs exhibited distinct biogeographic differences and were primarily affected by the spatial heterogeneity of soil nutrients. We found that the soil EES was strongly influenced by soil pH and mean annual temperature. Moreover, soil properties were found to be more important than climatic factors in influencing changes in soil microbial nutrient restrictions based on vector length (0.43 vs. −0.1). Random forest analysis indicated that changes in microbial nitrogen (N) and phosphorus (P) limitations were mainly affected by soil NO3−-N and dissolved organic carbon (DOC), whereas soil microbial C limitation was largely influenced by pH, DOC, and total C content. This study sheds light on how soil and climatic factors affect soil EES in subtropical Chinese fir plantation ecosystems and provides useful insights for the development of management strategies to improve the productivity of Chinese fir forests.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, β-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21–2.81 times) in β-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%−45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17–1.59 and 1.18–3.56 times, respectively) under heavy arsenic stress (500 mg kg−1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5–50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4–47.9% and 31.2–63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Restoring Subtropical Forests: Alleviating P Limitation and Introducing C Limitation Using Evergreen Broad-Leaved Tree Species

Determining which species to utilize for the artificial restoration of subtropical secondary forests has become a focal point in forestry and ecology. To compare the effects of the subtropical secondary forest artificial restoration model on soil microbial nutrient acquisition and limitation, we examined secondary forests (CKs), evergreen coniferous forests (GCPs), evergreen coniferous mixed broad-leaved forests (GCBMs), evergreen mixed broad-leaved forests (GBMs), and natural deciduous broad-leaved mixed forests (DBMs) as research subjects. Among them, GCPs, GCBMs, and GBMs were dominated by the species of the early, middle, and climax stages of subtropical forest succession, respectively. The activities and stoichiometry of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) in the topsoil were analyzed. The results showed that the forest type significantly affects the activities of BG and LAP rather than NAG or ACP. The BG activity in DBMs was the lowest, while the LAP activity in CKs was significantly higher than that in plantations. Furthermore, the nutrient limitation of microbes was quantitatively analyzed by using the vector analysis of enzyme stoichiometry. The soil microbes in the study area were co-limited by C and P, and the nutrient limitation was in the order of C > P > N. Among the forests, the enzyme stoichiometric ratios in GCPs and DBMs were closest to 1:1:1. From CKs to GBMs, the microbial C limitation was increased, while the P limitation was decreased. The C limitation in DBMs was slightly lower than that in CKs. Overall, the P limitation in evergreen plantations was less than that in CKs. The soil bulk density, C/P, and N/P significantly influenced enzyme activities and stoichiometry. These results suggest that the artificial restoration of subtropical forests using evergreen species alleviated P limitation, while using deciduous broad-leaved species offered potential for alleviating microbial C limitation. Compared with evergreen broad-leaved species, employing pioneer and mid-successional or deciduous broad-leaved species can better achieve balanced microbial nutrient requirements.

Soil stoichiometric imbalances constrain microbial-driven C and N dynamics in grassland

Grassland restoration leads to excessive soils with carbon (C) and nitrogen (N) contents that are inadequate to fulfill the requirements of microorganisms. The differences in the stoichiometric ratios of these elements could limit the activity of microorganisms, which ultimately affects the microbial C, N use efficiencies (CUE, NUE) and the dynamics of soil C and N. The present study was aimed at quantifying the soil microbial nutrient limitation and exploring the mechanisms underlying microbial-induced C and N dynamics in chrono-sequence of restored grasslands. It was revealed that grassland restoration increased microbial C, N content, microbial C, N uptake, and microbial CUE and NUE, while the threshold elemental ratio (the C:N ratio) decreased, which is mainly due to the synergistic effect of the microbial biomass and enzymatic stoichiometry imbalance after grassland restoration. Finally, we present a framework for the nutrient limitation strategies that stoichiometric imbalances constrain microbial-driven C and N dynamics. These results are the direct evidence of causal relations between stoichiometric ratios, microbial responses, and soil C, N cycling.

Microbial nutrient limitation along a 2-million-year dune chronosequence

Long-term ecosystem development is characterized by a switch from nitrogen (N) to phosphorus (P) limitation of plant communities as soils age, which leads to changes in plant biomass, diversity, and foliar nutrient concentrations. Similar effects occur belowground, although the extent to which nutrient availability is the primary driver of long-term changes in soil microbial communities remains uncertain. To investigate this, we assessed proxies for soil microbial nutrient limitation along the Jurien Bay dune chronosequence in Western Australia, where a long-term decline in P availability is reflected in strong variation in plant and microbial community composition over 2 million years of soil development. We quantified carbon (C), N, and P in the soil microbial biomass, assayed soil enzymes involved in the acquisition of those nutrients from soil organic matter, and used microbial stoichiometric ratios and vector analysis of enzyme activities to assess whether long-term changes in soil nutrient availability are reflected in nutrient demand by soil microbes. Concentrations of microbial nutrients peaked in Holocene soils (1–6.5 ky), although differences in microbial P were not significant. There were no significant differences in microbial nutrient ratios (C:N, C:P, and N:P) along the chronosequence. Acid phosphatase activity increased continually throughout the chronosequence, while the activities of leucine aminopeptidase and β-glucosidase were greatest in Holocene soils and declined with increasing soil age. Corresponding vector lengths indicated greater investment in C-degrading enzymes in Holocene soils (≤6.5 ky), while vector angles indicated greater investment in the acquisition of P compared with N in Pleistocene soils (≥120 ky). Overall, these findings show that changes in nutrient availability during long-term pedogenesis at Jurien Bay are reflected in microbial investment in nutrient acquisition, but that the soil microbial biomass exhibits a remarkable degree of homeostasis despite major shifts in nutrient availability and community composition over 2 million years of ecosystem development.

Climate change disrupts the seasonal coupling of plant and soil microbial nutrient cycling in an alpine ecosystem.

The seasonal coupling of plant and soil microbial nutrient demands is crucial for efficient ecosystem nutrient cycling and plant production, especially in strongly seasonal alpine ecosystems. Yet, how these seasonal nutrient cycling processes are modified by climate change and what the consequences are for nutrient loss and retention in alpine ecosystems remain unclear. Here, we explored how two pervasive climate change factors, reduced snow cover and shrub expansion, interactively modify the seasonal coupling of plant and soil microbial nitrogen (N) cycling in alpine grasslands, which are warming at double the rate of the global average. We found that the combination of reduced snow cover and shrub expansion disrupted the seasonal coupling of plant and soil N-cycling, with pronounced effects in spring (shortly after snow melt) and autumn (at the onset of plant senescence). In combination, both climate change factors decreased plant organic N-uptake by 70% and 82%, soil microbial biomass N by 19% and 38% and increased soil denitrifier abundances by 253% and 136% in spring and autumn, respectively. Shrub expansion also individually modified the seasonality of soil microbial community composition and stoichiometry towards more N-limited conditions and slower nutrient cycling in spring and autumn. In winter, snow removal markedly reduced the fungal:bacterial biomass ratio, soil N pools and shifted bacterial community composition. Taken together, our findings suggest that interactions between climate change factors can disrupt the temporal coupling of plant and soil microbial N-cycling processes in alpine grasslands. This could diminish the capacity of these globally widespread alpine ecosystems to retain N and support plant productivity under future climate change.

Microbial Nutrient Limitation of Different Tea Cultivars: Evidence from Five Representative Cultivars

Soil microbial activity is generally limited by the availability of carbon (C), nitrogen (N), or phosphorus (P) in agricultural ecosystems. Soil ecoenzymatic activity (EEA), ecoenzymatic stoichiometry (EES), and vector characteristics were examined to assess microbial nutrient limitation. Investigating soil microbial nutrient limitation can provide insight into nutrient cycling in tea plantations with different tea cultivars. However, the dynamics of different tea cultivars on soil microbial nutrient limitations and their effect on tea quality remains poor. To address this issue, soil and plant samples were collected from a tea plantation cultivating five representative tea cultivars in Hunan Province, China. Baojing Huangjincha No. 1 (HJC1) and Huangjincha No. 2 (HJC2) were the extra early-sprouting cultivars, Zhuyeqi (ZYQ) and Zijuan (ZJ) were the middle-sprouting cultivars, and Zhenghedabai (ZHDB) was the late-sprouting cultivar, respectively. The results indicated that differences in EEA and EES were significant among five treatments. Notably, ZYQ and ZJ exhibited markedly lower activities of carbon (C), nitrogen (N), and phosphorus (P) acquiring enzymes compared to HJC1 and HJC2, whereas ZHDB showed significantly higher ecoenzymatic activities. Despite a general limitation in C and P for soil microorganisms across all cultivars (VL ranging from 1.42 to 1.59 and VA ranging from 58.70° to 62.66°), the degree of microbial nutrient limitation varied. Specifically, ZYQ experienced a pronounced P limitation (VA = 62.66°, N:P enzyme = 0.52), as evidenced by increased vector angles and decreased N:P enzyme values. Although C limitation was most pronounced in ZYQ (VL = 1.59), it did not significantly differ among the cultivars. These findings suggest that tea cultivars can influence the P limitation of microbial communities. Further analysis revealed that microbial nutrient limitations might adversely affect tea quality via impeding enzyme secretion. This study highlights the critical role of nutrient cycling within the soil-microorganism-plant ecosystem and emphasizes the influence of soil microbial nutrient limitations on tea quality within tea plantations. It is recommended that in the management of tea plantation fertilization, managers need to consider the influence of cultivars and develop specialized cultivar fertilizers.

Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

Soil nutrient levels regulate the effect of soil microplastic contamination on microbial element metabolism and carbon use efficiency

Microplastics (MPs) are emerging environmental contaminants in soil ecosystems that disrupt the soil carbon (C) pool. Therefore, the response of microbial metabolism to MP-contaminated soil is crucial for soil-C stabilization. We undertook factorial experiments in a greenhouse with three types of soil microplastics with three levels of soil nutrients and undertook soil physiochemical analyses after 60 days. The present study revealed how the presence of degradable polylactic acid (PLA) and non-degradable polyethylene (PE) MPs affects soil microbial nutrient limitation and C use efficiency (CUE) at varying nutrient concentrations. The presence of PLA in soil with low nutrient levels led to a significant increase (29%) in the activities of nitrogen (N)-acquiring enzymes. In contrast, the presence of MPs had no effect on C- and N-acquiring enzymes. The occurrence of PE caused a 41% reduction in microbial C limitation in high-nutrient soils, and microbial nutrient metabolism was limited by the occurrence of MPs in soils amended with nutrients. A strong positive correlation between microbial C and nutrient limitation in the soil indicates that addressing C limitation followed by amendment of soil with MPs could potentially intensify microbial N limitation in soils with varying nutrients. In comparison, the microbial CUE increased by 10% with the application of degradable MPs (PLA) to soils with a low nutrient status. These findings highlight the significant influence of both degradable PLA and non-degradable PE MPs on soil microbial processes and C dynamics. In conclusion, PLA enhances metabolic efficiency in nutrient-rich soils, potentially aiding C utilization, whereas PE reduces microbial C limitation, offering promise for soil C sequestration strategies. Our findings underscore the importance of considering MPs in soil ecosystem studies and in broader sustainability efforts.

High level of winter warming aggravates soil carbon, nitrogen loss and changes greenhouse gas emission characteristics in seasonal freeze-thaw farmland soil

Changes in the soil environment caused by winter warming is affecting the carbon and nitrogen cycles of seasonal freeze-thaw farmland soil. A field experiment was conducted in a seasonal freeze-thaw farmland soil of northeast China to investigate the effects caused from different levels of warming (W1 + 1.77 °C, W2 + 0.69 °C and C + 0 °C) on soil carbon and nitrogen dynamics, microbial biomass and greenhouse gases fluxes. During the early and middle winter, the contents of all kinds of soil carbon and nitrogen (Ammonium, nitrate, total nitrogen, dissolved organic carbon, readily oxidizable organic carbon and soil organic carbon) tended to increase with the increase of warming level, while during the late winter, their contents under different temperature treatments roughly present trend of W2 ≥C > W1. Except for the late thawing period, warming increased the contents of soil microbial biomass carbon and nitrogen, during the late thawing period, with the increase of warming level, MBC and MBN decreased significantly. Warming would stimulate the release of greenhouse gases from soil. But due to the differences of soil environmental conditions in each period and soil nutrient dynamics under different treatments, which made the effects of different levels of warming on soil GHGs fluxes in different periods are different. Our study suggested that low-level warming improved the availability of soil carbon and nitrogen, increased the contents of microbial biomass and greenhouse gas emissions. However, although high-level winter warming showed a similar phenomenon in the early and middle winter to the low-level warming, during the late winter, high-level warming increased soil nutrients loss and broke the seasonal coupling relationship between crop nutrient acquisition and soil microbial nutrient supply, and even led to the adaptation of soil CO2 release to it. This is of great significance for exploring the carbon and nitrogen cycle mechanisms of global terrestrial ecosystem.

Adaptability of agricultural soil microbial nutrient utilization regulates community assembly under mulching measures on the Loess Plateau

Soil microbial nutrients and resource availability improve with mulching in agroecosystems, resulting in changes of soil microbial nutrient utilization strategies. However, the responses of soil microorganisms to nutrient utilization processes to regulate community assembly and thus maintain resource availability have not been clarified. Here, we performed a long-term field experiment with mulching measures, including no-mulching (NM), straw mulching (SM), plastic mulching (PM), and ridge mulching (RM), conducted on the Loess Plateau of China, to explore the community assembly process in response to microbial nutrient utilization. Microbial nutrient utilization strategies were analysed by measuring soil nutrients, microbial biomass, and extracellular enzyme activities. The results showed that PM and RM acquired C and N nutrients by secreting C- and N-extracellular enzymes in response to C:N- and C:P imbalances in soil chemistry, thereby reducing the nutrient limitation on microbial metabolism and improving microbial C utilization efficiency (CUE). Soil extracellular enzymatic stoichiometry increased and N utilization efficiency (NUE) decreased under mulching and drove an increase in beta-diversity and dominant species abundance in fungal communities. Mulching measures promoted the modular distribution of sensitive microorganisms and aggregation of fungal networks under PM and RM by reducing the stoichiometric imbalance and extracellular enzymatic N:P. At the same time, the microbial community assembly gradually changed from a stochastic to a deterministic process in response to the alleviation of soil C:P imbalance and changes in microbial nutrient utilization, in which the fungal community was dominant. In conclusion, soil microorganisms adaptively responded to changes in soil microbial nutrient utilization through the enhancement of aggregation of fungal co-occurrence networks and deterministic assembly processes. This study provides a better understanding of the impact of mulching on microbial nutrient utilization strategies from a community assembly perspective.

Long-term N addition leads to microbial C, but not N limitation of poplar plantation soils in eastern China

Soil extracellular enzymes are vital to regulating soil carbon (C) and nutrient cycling, and hence affecting soil function. However, how soil enzymes activity will respond to increasing global nitrogen (N) deposition, remains poorly understood. In this study, we applied five N addition treatments (0, 5, 10, 15, and 30 g m−2 yr−1) at a coastal China poplar plantation to explore the activity of the five soil enzymes associated with C, N, and phosphorus (P) cycling and nutrient limitation of soil microbes from 2018 to 2020. We found that N addition significantly increased C, decreased N and showed no significant impact on P acquisition enzyme activity. We also found that N addition aggravated soil microbial C limitation but did not significantly change the N limitation. Both soil microbial C and N limitation were eased with time (year). Best subset regression analysis (BSS) showed that dissolved organic C, soil pH, and microbial biomass C were the dominant drivers of C, N, and P acquisition enzyme activity, respectively. Also, BSS showed that soil available N explained the greatest proportion of variation in positive soil microbial C and negative N limitation. Our study provides evidence for changes in soil enzymes activity and microbial nutrients limitation, as well as contributes to the theoretical basis for soil microbial nutrient cycling with elevated N deposition.

Long-term successive rotation affects soil microbial resource limitation and carbon use efficiency in Chinese fir (Cunninghamia lanceolata) monoculture plantations

Long-term successive rotation has resulted in negative effects on stand productivity, soil nutrient pool and microbial diversity and function in monoculture tree plantations. However, how successive rotation influences soil microbial nutrient limitation and carbon use efficiency (CUE) and their linkage with resource carbon (C): nitrogen (N): phosphorus (P) stoichiometry remain largely unknown. To solve this puzzle, we compared the C:N:P stoichiometries of leaf litter, fine root and soil, as well as microbial biomass and enzyme activities among three Chinese fir (Cunninghamia lanceolata) plantations with first (FRP), second (SRP) and third (TRP) generations and a natural broad-leaved forest (BL). We found that long-term successive rotation of Chinese fir decreased litter biomass by 64.7% ∼ 80.9% and enhanced litter C:N ratio by 2.7% ∼ 36.0% compared to the BL. Successive rotation decreased the contents of dissolved organic C, total N, and soil C:P and N:P ratios, and resulted in an increased C:N imbalance between soil microorganisms and nutrients in the TRP generation. Long-term successive rotation increased microbial C limitation by 1.5% ∼ 11.1% but decreased N and P limitations by 127.3% ∼ 160.9% and 15.3% ∼ 37.5%, compared with the BL, and resulted in significant increases in microbial CUE and substrate-induced respiration rate of C to N sources in the TRP generation. Structural equation modeling suggested that successive rotation indirectly affected microbial CUE and SIR by changing litter C:N, enzyme C:N and soil C:N imbalance. Collectively, these findings indicated that long-term successive rotation aggravated soil microbial C (energy) limitation and affected microbial CUE and capacity due to the increased stoichiometric imbalance between their resources. Future management practices that could increase litter and soil quality could be helpful to decrease microbial C limitation and maintain microbial functionality for sustainable monoculture plantations.

Stronger microbial nutrient limitations in subsoil along the precipitation gradient of agroecosystem: insights from soil enzyme activity and stoichiometry

IntroductionSoil extracellular enzymes are central in terrestrial ecosystem responses to climate change, and their research can be crucial for assessing microbial nutrient demand. However, the effects of climate-induced precipitation patterns on soil microbial nutrient demand in different soil profiles of agroecosystems are rarely studied.MethodsHere, we present how the precipitation gradient affects soil enzymes related to carbon (C), nitrogen (N) and phosphorus (P) cycling and identified microbial nutrient limitation determinants at five depth intervals (0–10, 10–20, 20–30, 30–40, and 40–50 cm) in seven agroecosystems.Results and DiscussionWe found that N- and P-acquiring enzymes have a tendency to decrease or increase, respectively, but C-acquiring enzymes did not change along the precipitation gradient throughout soil profiles. Soil pH and moisture were the most important factors affecting the enzyme activity in 0–50 cm. Our results also revealed a crucial soil boundary (at 20 cm) that differentiated responses of microbial nutrient limitation to precipitation changes. In the topsoil (0–20 cm), the stoichiometry of soil nutrients did not vary with precipitation. Microbial P limitation was exacerbated with increased precipitation, which was controlled by soil pH and moisture in the topsoil. In contrast, in the subsoil (20–50 cm), soil nutrient stoichiometry decreased with increasing precipitation, and microbial C and P limitation displayed a positive correlation with precipitation. Furthermore, microbial P limitation tended to be stronger in the subsoil than in the topsoil along the precipitation gradient. Microbial C and P limitation was regulated by the soil nutrients and their stoichiometry in the subsoil. Our study is an essential step in soil enzyme activity and stoichiometry response to precipitation in agroecosystems and provides novel insights into understanding microbial nutrient limitation mechanisms in soil profiles along the precipitation gradient.