Search Results (109)

Soil extracellular enzymes serve as critical drivers in the cycling of nutrients within ecosystems, and their stoichiometry can effectively reveal the metabolic resource limitations of soil microorganisms. However, extracellular enzyme activities, microbial metabolic characteristics, and their influencing factors in different grassland types in the Qilian Mountains have rarely been studied. This study focuses on alpine meadows (TJs), swampy meadows (HBs), and temperate desert grasslands (DLHs) in the Qilian Mountains. Extracellular enzyme activity and stoichiometric characteristics in the 0–30 cm soil layer were analyzed to explore the limiting factors on microbial metabolism and clarify the main driving factors affecting nutrient limitation. Compared with swampy meadows and temperate desert grasslands, alpine meadows exhibited greater extracellular enzyme activity, as revealed by the results. Statistical analysis revealed that enzyme activity exhibited a significant positive correlation with nitrate nitrogen (NO₃⁻-N), total phosphorus (TP), total potassium (TK), available potassium (AK), and dissolved organic carbon (DOC), while showing a significant negative correlation with soil moisture content (SWC) (p < 0.05). Vector analysis of soil enzymes showed that soil microorganisms in the three grassland types are limited by carbon (C) and phosphorus (P). Among them, DLH microorganisms are highly restricted by carbon, while HB microorganisms are highly restricted by phosphorus. Random forest results showed that total phosphorus (TP), available potassium (AK), nitrogen-to-phosphorus ratio (N: P), nitrate nitrogen (NO₃⁻-N), and readily oxidizable carbon (ROC) contribute significantly to vector length, while total potassium (TK), soil organic carbon (SOC), particulate organic carbon (POC), bulk density (BD), and carbon–nitrogen ratio (C: N) contribute significantly to vector angle. A partial least squares path model (PLS-PM) revealed that although microbial metabolic limitation is influenced by specific soil factors, the comprehensive effect of soil physicochemical properties is the dominant factor regulating microbial carbon and phosphorus limitation. This study provides valuable data and insights that elucidate the metabolic characteristics of soil microorganisms across different grassland types in the Qilian Mountains, thereby improving the mechanistic understanding of soil nutrient cycling and supporting evidence-based strategies for the sustainable management and conservation of these fragile ecosystems. Full article

Vegetation mosaics characterize mountainous agroforestry ecosystems, yet how their spatial configuration shapes soil microbial assembly and functions remains unresolved. This study investigated how mosaic elements (monocultures, shrublands, and ecotones) drive microbial communities and enzyme activities across a forest–shrubland–farmland mosaic in western Hunan, China. Nutrient stoichiometry, microbial biomass (PLFA), and six enzyme activities were analyzed via variance partitioning, partial least squares regression, and ordination analysis. Fungal biomass dominated, peaking in ecotones and showing the lowest values in monocultures and shrublands. Microbial assembly was regulated by soil nutrients (31%) rather than soil texture (15%). Fungi (variable importance in projection, VIP = 1.287) and bacteria (VIP = 1.003) were key drivers, indicating distinct functional compartmentalization: fungi drove oxidative enzymes, whereas bacteria mediated nutrient cycling. Actinomycetes and total PLFA acted as secondary drivers, with VIP values of 0.932 and 0.939, respectively. Soil organic matter, dissolved organic carbon, silt content, and available nitrogen were key abiotic predictors. Collectively, vegetation configuration regulates soil functioning via nutrient-mediated microbial assembly and functional differentiation across mosaic elements. These findings underscore the role of landscape heterogeneity in sustaining soil fertility, suggesting that protecting ecotones and maintaining mosaic complexity should be prioritized in mountainous agroforestry management to enhance soil ecological functioning under global land-use change. Full article

The ecological restoration of degraded sandy land in the Yarlung Zangbo River Valley is constrained by the metabolic functions of soil microorganisms. This study investigates the dynamic mechanisms of microbial elemental use efficiency in walnut plantations, with a focus on seasonal variations in soil chemical stoichiometry, extracellular enzyme activity, and microbial nutrient efficiency in rhizosphere and bulk soils. This paper explores the effects of conventional organic fertilizer (CF) and organic–inorganic compound fertilizer (OIF) on microbial nutrient use strategies and their seasonal dynamics. The results showed significant seasonal fluctuations in soil active nutrients and microbial biomass, while the total nutrient content remained stable. OIF enhanced microbial chemical stoichiometric homeostasis but simultaneously triggered a “carbon–phosphorus metabolic trade-off”, leading to a restraint of microbial carbon use efficiency (CUE) during the growing season. Microbial elemental use efficiency (EUE) exhibited clear seasonal differentiation: CUE was higher in summer, promoting biomass accumulation, whereas NUE and PUE increased in winter and spring, reflecting a nutrient conservation strategy. The EUE pathways were decoupled between rhizosphere and non-rhizosphere microenvironments. The rhizosphere was more directly driven by soil chemical stoichiometry and microbial biomass, while the non-rhizosphere was influenced by nutrient limitation states, represented by vector characteristics. This study provides insights into the seasonal adaptability and microenvironmental heterogeneity of microbial metabolism during the restoration of cold sandy land. It is suggested that future ecological management should focus on N-P balanced fertilization and consider the differential responses between rhizosphere and non-rhizosphere zones to enhance ecosystem productivity and soil carbon, nitrogen, and phosphorus sequestration potential. Full article

To elucidate the mechanisms of nutrient cycling in rhizosphere soil and microbial metabolism during the prolonged continuous cropping of lavender, this study examined the rhizosphere soil of lavender with different continuous cropping years (1, 4, 7, 10, 15, and 20 years) in the Ili River Valley of Xinjiang, China, measuring physicochemical properties, microbial biomass C/N/P, and eight extracellular enzyme activities. Microbial carbon use efficiency (CUE) and nutrient limitation were quantified using vector analysis, threshold elemental ratios (TERs), and two derived indices (TER_EEA and TER_L). Soil properties exhibited distinct nonlinear patterns: SOC peaked at 4 years (p < 0.05), TN was highest at 20 years, and TP was lowest at 4–7 years. MBC and MBN peaked at 20 years, whereas MBP was significantly lower than in 1-, 4-, and 10-year fields (p < 0.05). EEC and EEN were highest at 20 years, while EEP was lowest at 4 years (p < 0.05). The activity of carbon-related acquisition enzymes increases from 134.81 μmol/g·h in the first year to 393.86 μmol/g·h in the 20th year, an increase of 192%; the activity of nitrogen acquisition enzymes increases from 686.11 μmol/g·h in the first year to 1430.58 μmol/g·h in the 20th year, an increase of 108%. This indicates that the decomposition of organic matter and the nutrient cycling capacity continue to enhance. Vector analysis showed a mean VA of 46° and VL of 0.25, with VA > 45° (P limitation) at 1–4 years shifting to VA < 45° (N limitation) at 20 years. Critically, TEREEA and TERL produced opposite dominant limitations due to differing normalization frameworks—TEREEA scales by microbial biomass stoichiometry—while TERL normalizes against enzyme-derived thresholds. CUET and CUEE ranged from 0.42 to 0.56, with the minimum at 10 years and relatively high values at 15–20 years (p < 0.05). RDA identified CBH (26.2%) and NO₃⁻–N (19.8%) as primary drivers, with extractable phosphorus exhibiting the strongest regulatory effect (pseudo-F = 26.0). These results demonstrate that multi-model stoichiometric assessment is essential, as single indices may yield contradictory diagnoses. These results demonstrate that multi-model stoichiometric assessment is essential, as single indices may yield contradictory diagnoses, and the observed nonlinear shifts in dominant limitation type provide a mechanistic basis for targeted nutrient management in sustainable lavender cultivation. Full article

Soil organic carbon (SOC) responses to straw return are strongly influenced by active carbon dynamics and extracellular enzyme responses, yet how these processes vary with initial SOC status and long-term straw-return history remains unclear. To address this question, we conducted a controlled incubation experiment using soils from long-term straw removal (CK) and straw return (SR) plots at two sites with contrasting SOC levels: a carbon-poor fluvo-aquic soil in Quzhou (QZ) and a carbon-rich black soil in Gongzhuling (GZL). Three fresh-straw input levels were imposed, and CO₂ release, SOC, labile C and N pools, extracellular enzyme activities, and ecoenzymatic stoichiometry were determined. Fresh-straw input markedly stimulated carbon mineralization in both soils, but SOC responses differed substantially. In QZ, SOC increased 12.1–15.7% at day 7 (vs. T0) and remained 6.7–12.1% above the control at day 90 under the long-term straw-return background. In contrast, GZL showed only minor early SOC responses, and doubled straw input reduced SOC 4.9–9.5% at day 90 despite a stronger dissolved organic carbon (DOC) pulse and greater cumulative CO₂ release. Enzyme responses also differed between soils: higher straw input in QZ enhanced β-cellobiohydrolase (CBH), β-xylosidase (BX), and especially L-leucine aminopeptidase (LAP), accompanied by lower ecoenzymatic C:P and higher vector angle, whereas GZL showed later activation of CBH, BX, and NAG with only slight changes in vector angle. Overall, our results indicate that initial SOC status and long-term straw-return history jointly regulate whether fresh-straw input promotes net SOC accumulation or enhanced mineralization. Full article

Clarifying the responses of microbial communities in distinct microhabitats like roots, the soil, and litter layers to secondary succession is critical for predicting the effects of global climate change on ecosystem functions. We investigated the microbial activities, compositions, and networks in these microhabitats of Fagus lucida forests ranging from 40 to 200 years. The results showed that soil physicochemical properties decreased with forest succession, except for NH₄⁺-N and available phosphorus, which decreased at the early stage. All vector angles of extracellular enzyme stoichiometry that were greater than 45° indicated that phosphorus was the key limiting element for microorganisms. The microbial community shifted from r- to K-strategists with forest succession, displaying the replacement of most bacterial phyla by Proteobacteria and Acidobacteriota, and an increase in the Acidobacteriota: Proteobacteria ratio, especially in the soil and litter layers. Soil properties, particularly NH₄⁺-N and pH, significantly affected the bacterial diversity and structure. Moreover, the bacterial network complexity increased with succession, particularly in the litter layer, and the topological properties of bacterial networks showed a stronger influence on microbial activities compared with those of fungal networks. The richness of keystone taxa in the litter layer was higher than in the soil layer and roots. However, the fungal community dominated by symbiotrophs showed lower sensitivity to soil nutrient changes and greater resilience to forest succession, displaying stable diversity and decreased network complexity, particularly in the roots. Ectomycorrhizal fungi (e.g., Russula) dominated the fungal guilds, and their abundance increased with forest succession, accompanied by a decrease in pathogenic fungi. Plant roots with significantly higher phosphatase activities played a stronger role than soils in structuring the litter microbial community, as reflected by similar carbon- and nitrogen-acquiring enzyme activities, microbial compositions, a greater share of taxa, and closer community distance. Our results revealed the increasingly important role of plant roots with forest succession in structuring the microbial community and nutrient cycling in the soil and litter layers. Full article

Functional microbial inoculation is widely applied in soil restoration; however, its effects on aggregate-scale nutrient cycling remain unclear. Based on ecological stoichiometry theory, we conducted 1-year and 3-year pot experiments using Bacillus thuringiensis (NL-11) and Gongronella butleri (NL-15) under plant-present and plant-absent conditions, with only NL-11 applied in the 1-year experiment. Aggregate size distribution, mean weight diameter (MWD), soil nutrients, microbial biomass, and enzyme activities were evaluated across aggregate classes. The results demonstrated that microbial effects were dependent on both time and plant presence. Under 3-year plant-present conditions, NL-11 and NL-15 significantly increased macroaggregate proportions and MWD, thereby enhancing aggregate stability. Under 3-year no-plant conditions, NL-15 increased organic carbon and total nitrogen in macro- and meso-aggregates by 55–59% and elevated soil C/P and N/P ratios, whereas NL-11 primarily enhanced total nitrogen. In 1-year no-plant macroaggregates, NL-11 increased microbial biomass phosphorus and reduced microbial biomass C/P and N/P ratios. Both inoculants enhanced invertase activity under plant-absent conditions, whereas plant presence stimulated acid phosphatase activity, with NAG activity increasing only under NL-15. Overall, microbial inoculation altered nutrient availability and microbial metabolic characteristics, promoted coordinated C–N–P stoichiometry, and facilitated the recovery of aggregate-scale nutrient cycling. Full article

Red soils suffer from nutrient imbalances and low-phosphorus availability. Rational intercropping plays an important role for increasing crop yield and improving nutrient use efficiency, while its long-term effects on biogeochemical cycles and ecological stoichiometric stability are poorly understood. Based on a 7-year continuous field experiment in low-phosphorus red soil, the soil enzyme activity, soil carbon (C), nitrogen (N), phosphorus (P) and C:N:P content, soil microbial biomass (MBC, MBN, MBP), and their ecological stoichiometric characteristics in maize monoculture (MM) and maize//soybean intercropping (MI) under four phosphate fertilization gradients (0, 60, 90, 120 kg P₂O₅ hm⁻²) were investigated. The impacts of continuous MI on soil CNP ecological stoichiometric stability in red soil were studied. The results showed that intercropping significantly elevated the content of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and microbial biomass (MBC, MBN, MBP). Compared to maize monoculture, the contents of SOC, TN, and TP in intercropping soils increased by an average of 26.01%, 12.08%, and 7.58%, respectively, and soil MBC, MBN, and MBP increased by an average of 40.87%, 29.50%, and 38.34%, respectively, across different phosphate application gradients. Intercropping also significantly enhanced the activities of key C-, N-, and P-cycling enzymes (β-glucosidase, urease, acid phosphatase), increased by an average of 33.47%, 14.69%, and 60.15%, respectively. Most importantly, intercropping substantially improved the stoichiometric homeostasis of the microbial biomass and decreased the homeostasis index 1/H of MBC, MBN, MBP. Continuous intercropping shifted MBN from a sensitive to a strongly homeostatic state, MBP to homeostatic and the MBC/MBP ratio from weakly to strongly homeostatic in red soil. In conclusion, continuous MI in low-P red soil demonstrably increases soil nutrient content, enhances soil enzyme activity, and promotes ecological stoichiometric stability. This system represents one of the optimized cropping models for the synergistic enhancing of soil ecological stability in red soil regions. Full article

In forest ecosystems, rhizodeposition can lead to significant differences in the availability of soil carbon (C), nitrogen (N), and phosphorus (P) between rhizosphere and bulk soils. Soil stoichiometry affects microbial and enzyme nutrient content and determines the abundance and composition of microbes and thus regulates microbial carbon use efficiency (CUE). However, how soil stoichiometry—particularly its variation between the rhizosphere and bulk soil—regulates microbial CUE by shaping microbial biomass, extracellular enzyme stoichiometry, and community composition remains insufficiently quantified. Here, through the C:N, C:P, and N:P ratios for available soil nutrients, microbial biomass, and extracellular enzyme activities—(β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminodase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP))—and the composition and activity of microbial communities (based on sequencing of bacterial 16S rRNA and fungal ITS genes) in the rhizosphere and bulk soils of five temperate forest ecosystems in northeastern China, we aimed to unravel their integrated effects on microbial CUE. Results indicated that soil C, N, and P and their stoichiometry, microbial community composition, and microbial CUE were significantly different between rhizosphere and bulk soils among all tree species. The disproportionate variation in soil nutrient pools between the rhizosphere and non-rhizosphere regions has led to a stoichiometric imbalance. There was higher microbial CUE in the rhizosphere soil than that in the bulk soil among all tree species. However, the effect pathways of tree species on microbial CUE in the rhizosphere and bulk soils differed. The structural equation model (SEM) further suggested that tree species affected microbial CUE through distinct pathways in different soil compartments. In the rhizosphere, the effect was directly driven by available nutrient stoichiometry. In bulk soil, it was jointly mediated by both available nutrients and microbial biomass stoichiometry. These findings demonstrate that root rhizodeposition shapes microbial carbon cycling by altering soil stoichiometric imbalances, which can strengthen the current understanding of plant–microbe–soil interactions in temperate forests. Full article

Microbial stoichiometry serves as a fundamental indicator of nutrient limitations in microbial communities. However, the dynamic effects of Pugionium Gaertn. growth on soil microbial C:N:P stoichiometric ratios and their primary driving factors in native desert ecosystems remain poorly understood. This study aimed to clarify the stage-dependent regulation of microbial C:N:P stoichiometry by Pugionium Gaertn. in native desert ecosystems. This study examined representative Pugionium Gaertn. (P. cornutum and P. dolabratum) in northwestern China’s desert regions, based on investigations conducted during 2022–2023, conducting systematic analysis of variations in rhizosphere soil microbial biomass C, N, and P levels, C:N:P stoichiometric ratios, fungal and bacterial diversity, soil physicochemical properties, and extracellular enzyme activities (EEAs) across different phenological stages. Results demonstrated that Pugionium Gaertn. growth significantly enhanced microbial biomass C, N, and P accumulation during vigorous growth stages. Simultaneously, stoichiometric ratios (C:N, C:P, N:P) exhibited periodic fluctuations, with P limitation characteristics becoming substantially intensified during the reproductive stage. Total soil nitrogen, total phosphorus, and EEAs significantly regulated microbial C:N:P stoichiometric ratios through their effects on bacterial diversity. In P. dolabratum, distinct response pathways were observed between fungi and bacteria to P limitation, indicating species-specific regulatory mechanisms. These findings provide novel insights into the relationship between Pugionium Gaertn. and soil elemental stoichiometry, as well as its influence on elemental dynamic balance at microbial and community levels. Furthermore, the results support ecological adaptation strategies of Pugionium Gaertn. communities in native habitats, offering scientific evidence for vegetation restoration and soil improvement in desert regions. Full article

Monitoring the soil–plant system in forest ecosystems is crucial for preserving their ecological functions and services. This study assessed carbon and nitrogen stable isotopes and ecoenzymatic stoichiometry as suitable indicators for characterizing the soil–plant system as a functional unit of ecological processes. To this end, in June 2021 six plots (1 m² each) were selected in two typical Mediterranean forest ecotypes: a coastal stone pine forest (Pinus pinea L., PF) and a meso-hygrophilous broadleaf forest (RV). Soil samples (0–15 and 15–30 cm depth) and litter samples (40 × 40 cm) were collected and characterized in terms of physical, chemical and biochemical properties. t-tests revealed significant differences between RV and PF, indicating distinct microbial nutrient acquisition strategies. The higher C:N ratio in PF suggested lower litter quality and greater recalcitrance to microbial decomposition. Consistently, RV showed a more pronounced ¹³C and ¹⁵N enrichment from litter to SOM down to a 30 cm depth, confirming faster organic matter decomposition and mineralization. Enzyme activity patterns supported these findings. The higher β-glucosidase and butyrate esterase activities in RV reflected its greater microbial potential to activate biogeochemical cycles. Both forests exhibited a higher microbial demand for C and P than for N to maintain ecological stoichiometric balance, with stronger C limitation at the surface and P limitation in the subsoil, particularly in RV soil. This integrated monitoring approach provides insights into nutrient cycling and ecosystem resilience and offers tools to evaluate ecosystem functionality under changing environmental conditions, supporting sustainable forest management. Full article

Soil extracellular enzyme activity reflects microbial resource acquisition and metabolic efficiency. However, applying enzyme stoichiometry to explore microbial metabolic limitations and carbon use efficiency (CUE) in rhizosphere and bulk soils under saline conditions remains limited. In this study, rhizosphere and bulk soils of Tamarix austromongolica were sampled along a salinity gradient in the Yellow River Delta to assess microbial metabolic limitation and CUE. Results showed that increasing salinity intensified microbial metabolic limitations and markedly reduced CUE, identifying salinity as the dominant factor constraining microbial efficiency. Rhizosphere soils consistently exhibited phosphorus limitation, whereas bulk soils shifted from balanced N–P limitation to pronounced N limitation with increasing salinity. Despite stronger microbial C limitation, CUE remained significantly higher in the rhizosphere than in the bulk soils, suggesting that continuous carbon inputs and enhanced enzyme activity partially mitigated salinity-induced stress. These findings highlight the complex interplay between salinity stress and rhizosphere effects in regulating microbial nutrient acquisition and carbon metabolism. Overall, this study demonstrates the utility of enzyme stoichiometry for evaluating microbial functional adaptation in saline habitats and provides insights that may contribute to the theoretical basis for vegetation restoration in saline-alkali ecosystems. Full article

Headwater streams comprise almost 90% of global river networks, and their microorganisms play critical roles in organic matter decomposition and nutrient cycling. These functions, however, are affected by recurrent drying and rewetting. This study examined spatial variation in microbial enzyme activity tied to organic carbon degradation (β-glucosidase, phenol oxidase, and peroxidase) and nitrogen (N-acetylglucosaminidase) and phosphorus (phosphatase) mineralization in water, epilithic biofilm, leaf litter, and sediment in two intermittent streams: Gibson Jack Creek (Idaho, USA) and Pendergrass Creek (Alabama, USA), representing different climactic and physiographic settings. Microbial activity was greater in Gibson Jack Creek, where the activity of leaf litter enzymes varied along the stream network, and there were strong correlations in microbial activity between different stream habitats. Microbial activity in Pendergrass Creek showed primarily within-habitat associations. Activity in water, sediment, and biofilm showed broader spatial heterogeneity in both stream networks. Ratios of microbial activity (enzyme stoichiometry) suggested that microbial communities in both systems were primarily limited by carbon and phosphorus, although there was more spatial variation in nitrogen limitation, particularly in water and sediment at Pendergrass Creek and in biofilm at Gibson Jack Creek. These findings underscore the spatial heterogeneity and environmental sensitivity of microbial processes in intermittent streams. Full article

Understanding how straw incorporation affects soil stoichiometry and biochemical processes is essential for improving soil fertility in dryland wheat systems on the Loess Plateau. We quantified effects of four wheat straw return rates [0 (W0), 3500 (W1), 7000 (W2), and 14,000 kg ha⁻¹ (W3)] on C-N-P stoichiometry, microbial biomass, active carbon fractions, and enzyme activities in a randomized block experiment in Dingxi, Gansu. Composite soil samples from 0–10, 10–20, and 20–30 cm were analyzed for soil organic carbon (SOC); total nitrogen (TN); total phosphorus (TP); microbial biomass C, N, and P; dissolved, particulate, and readily oxidizable organic C; and sucrase, urease, alkaline phosphatase, and catalase activities. Increasing straw input significantly increased SOC, TN, and TP across all depths, with W3 increasing them by up to 42, 33, and 24% relative to W0, respectively. Under W3, microbial biomass C and N more than doubled, and labile C fractions and enzyme activities increased by 35–80% compared with W0. Straw return also modified soil and microbial C:N:P stoichiometry, decreasing microbial C:N and C:N:P and increasing N:P, suggesting alleviated N limitation. Overall, moderate-to-high straw incorporation improved soil fertility and functioning, supporting straw return as a sustainable management practice for Loess Plateau drylands. Full article

The effect of nitrogen (N) deposition on soil organic carbon (SOC) and the underlying mechanisms in grassland ecosystems remain a topic of debate. Moreover, previous research has primarily concentrated on interaction between carbon (C) and N cycles in response to N deposition, with less attention paid to how N-induced phosphorus (P) deficits impact SOC sequestration. To further investigate whether soil microbial stoichiometry influences SOC sequestration under N enrichment, we conducted a field experiment involving N and P additions. The soil properties, nutrients within plant leaves and microbial biomass, and the potential activity of eco-enzymes related to microbial nutrient acquisition were measured. Results showed that SOC did not significantly change with N addition, and SOC significantly increased with addition of N and P together, which suggested that the SOC was depleted with N addition. Soil available phosphorus and microbial biomass phosphorus (MBP) did not significantly decrease alongside N addition, which suggested that microbes alleviated P limitation. Microbial metabolic limitation analysis showed microbial P limitation was enhanced by N10 treatment. At the same time, microbial P limitation enhanced microbial C limitation. Consequently, microbes also required more C as an energy resource to invest in enzyme production. Microbial P and C limitations were both significantly negatively correlated with SOC. Results from SEM analysis also showed that the MBC:MBP ratio was significantly negatively correlated with SOC. These results support the idea that consumer-driven nutrient recycling shapes the dynamics of SOC. Therefore, nitrogen deposition-induced MBC:MBP imbalance may regulate SOC in alpine grassland ecosystems. Full article