Search

Purpose: Incorporating rice straw into upland has been adopted as a strategy to increase crop productivity and decrease poisoning to rice from reducing substances accumulation as well as mitigate methane emission from paddy fields in South China. However, the mechanism underlying long-term ex situ incorporation of rice straw in upland on soil organic carbon (SOC) and crop yields through microbial metabolism remains unclear. Materials and methods: Hence, a field experiment was established to investigate the response mechanism of SOC and crop yields underlying microbe-mediated carbon dynamics with nutrient stoichiometry by ex situ incorporation of rice straw in upland. Results and discussion: The results showed that the treatment of cropping with chemical fertilizers plus rice straw (SCF) had the highest SOC accumulation rate (0.14 ± 0.03 g C kg−1 yr−1) during the 22-year experimental period. The mean yields of rapeseed and sweet potato were increased by 5.0% and 4.7% in the SCF treatment, correspondingly, compared with the treatment of cropping with chemical fertilizers (CF). Additionally, based on ecoenzymatic stoichiometry, soil microorganisms were found to be co-limited by carbon and phosphorus, which was aggravated by the decrease of soil available nutrients. The SCF treatment exhibited a higher soil microbiomass, resulting in an increased secretion of ecoenzymatic activities to mediate stoichiometric imbalance and mitigate nutrient competition between plant and microbial nutrient limitations. The findings revealed a significant association between stoichiometric imbalance and both SOC and crop yields, respectively. Conclusions: Therefore, our study indicated that long-term ex situ incorporation of rice straw in upland could be adopted as an effective agricultural management strategy to improve SOC and crop yields. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) as emerging contaminants have a global occurrence, including both terrestrial and marine ecosystems. Soil enzymes contribute to maintaining ecosystem multifunctionality, for example, nutrient cycling, organic material decomposition, and carbon and climate regulation. Our present review highlights the impacts of MPs on soil enzyme activities, influencing factors, and the underlying mechanisms. Increasing findings confirm that MPs can change the activities of a range of soil enzymes involved in the biogeochemical cycling of C and N. However, current results are highly controversial. The effects of MPs highly vary from significant to nonsignificant and are dependent on polymer type, biodegradability, dosage, size, shape, and aging degree of MPs, and exposure conditions. Compared to traditional MPs, biodegradable MPs generally show more pronounced effects. MPs can change soil enzyme activities via different pathways. On one hand, MPs can directly change soil enzyme structure, leading to alterations in enzyme activity. On the other hand, MPs can create unique habitats, provide carbon sources for specific functional microbes producing enzymes, and release plastic additives and pollutants disturbing the production of these enzymes. Furthermore, MPs can alter soil physicochemical and biological properties, the availability of substrates, plants and soil fauna, regulating soil enzymes and their functions. In conclusion, MPs can regulate soil enzyme activities and pose a profound impact on ecosystem multifunctionality. [ABSTRACT FROM AUTHOR]

Purpose: The influence of organic amendments on the interplay among soil extracellular enzyme activities (EEAs) and their stoichiometry (EES) and nutrient availabilities, key indicators of resource limitations for soil microbes, is poorly understood. This study aims to investigate how manure compost (hereafter "manure") and its biochar derivative affect EEAs, EES and soil fertility. Materials and methods: We studied EEAs (BG, β-glucosidase; CBH, cellobiohydrolase; LAP, Leucine aminopeptidase; NAG, β-1,4-N-acetylglucosaminidase and AP, acid phosphatase), EES and soil fertility two years post-application of manure and biochar in central Alberta, Canada. Results and discussion: Applying manure and its biochar did not affect soil permanganate oxidable carbon (C), total phosphorus (P), and available P and nitroegn (N). Manure application increased NAG activity by 13.9% (75.9 nmol h−1 g−1 soil) relative to the control (66.6 nmol h−1 g−1 soil), whereas biochar application increased LAP activity by 22.1% (64.6 nmol h−1 g−1 soil) compared to the manure treatment (52.9 nmol h−1 g−1 soil), suggesting that manure addition caused microbial C limitation, while biochar addition led to microbial N limitation. However, both manure and biochar treatments did not affect soil NAG, CBH and AP, and enzymatic C:N, C:P, and N:P stoichiometry. Manure and biochar and their interactions with the soil ultimately affect soil physicochemical properties. Conclusions: Manure and its biochar differentially altered some soil N-cycling EEAs and C and N limitations two years after their applications. [ABSTRACT FROM AUTHOR]

Alpine ecosystems are important terrestrial carbon (C) pools, and microbial decomposers play a key role in litter decomposition. Microbial metabolic limitations in these ecosystems, however, remain unclear. The objectives of this study aim to elucidate the characteristics of microbial nutrient limitation and their C use efficiency (CUE), and to evaluate their response to environmental factors. Five ecological indicators were utilized to assess and compare the degree of microbial elemental homeostasis and the nutrient limitations of the microbial communities among varying stages of litter decomposition (L, F, and H horizon) along an altitudinal gradient (2800, 3000, 3250, and 3500 m) under uniform vegetation (Abies fabri) on Gongga Mountain, eastern Tibetan Plateau. In this study, microorganisms in the litter reached a strictly homeostatic of C content exclusively during the middle stage of litter decomposition (F horizon). Based on the stoichiometry of soil enzymes, we observed that microbial N- and P-limitation increased during litter degradation, but that P-limitation was stronger than N-limitation at the late stages of degradation (H horizon). Furthermore, an increase in microbial CUE corresponded with a reduction in microbial C-limitation. Additionally, redundancy analysis (RDA) based on forward selection further showed that microbial biomass C (MBC) is closely associated with the enzyme activities and their ratios, and MBC was also an important factor in characterizing changes in microbial nutrient limitation and CUE. Our findings suggest that variations in MBC, rather than N- and P-related components, predominantly influence microbial metabolic processes during litter decomposition on Gongga Mountain, eastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The extent to which soil enzyme activity in assessing soil nutrient availability is useful has been controversial. In this review, we discuss the utility of ecoenzymatic stoichiometry (i.e. the ratio of nutrient- to carbon (C)-acquiring enzyme activities) on the basis of the resource allocation model for ecoenzyme synthesis. Both the selection of appropriate enzymes and the balance between relative amounts of substrates and enzymes in the soil are decisive factors in utilizing the ecoenzymatic stoichiometry. Ecoenzymatic stoichiometry can evaluate the availability of nitrogen (N), phosphorus, and sulfur in many soils in which the enzyme catalytic reactions are substrate-limited but not enzyme-limited. However, the ecoenzymatic stoichiometry approach does not seem to be applicable in soils where microbes are limited by factors other than nutrient availability, such as low temperature, where the enzyme catalytic reactions are enzyme-limited. Certain enzymes, such as N-acetyl-β-glucosaminidase and protease, appear to be insensitive to soil N availability, because they release compounds containing both N and C which serve as sources for both N and C/energy. We propose the use of enzymes such as L-asparaginase and urease as N-acquiring enzymes that release a compound containing N but not C (i.e. NH4+) as the hydrolysis product. Ecoenzymatic stoichiometry can be considered as an indicator of long-term (weeks) temporally integrated soil nutrient availability, rather than instantaneous availability, for plants as well as microbes, because of (i) the long-term persistence of extracellular enzymes in soils; (ii) a significant correlation between ecoenzymatic stoichiometry and the measurements reflecting the quantity of long-term available nutrients in soil; and (iii) a significant correlation between ecoenzymatic stoichiometry and plant nutrient uptake. This review also identifies challenges in assessing microbial nutrient limitation using ecoenzymatic stoichiometry. With a comprehensive understanding of underlying mechanisms and limitations, ecoenzymatic stoichiometry can be used as a biologically relevant indicator of nutrient availability in combination with other approaches such as conventional chemical extraction methods and the nutrient addition approach. [ABSTRACT FROM AUTHOR]

Background and aims: Vegetation restoration by altering soil properties has far-reaching impacts on soil extracellular enzyme activities (EEAs) and stoichiometry (EES). However, the response of EEAs and EES to changes in various soil properties along long-term vegetation restoration chronosequences in metal mining areas is still unrevealed. Methods: Soil organic carbon (SOC), nutrients such as total nitrogen (TN) and total phosphorus (TP), microbial biomass, physicochemical properties, heavy metals (Cd, Cr, Cu, Ni, V, and Zn), EEAs, and EES are appropriately analyzed along the chronosequence. Results: The EEAs exhibited an increasing trend at the early stage (0–15 years), which continued at high levels or increased thereafter at the late stage (16–49 years). The results also indicate that the enzyme C:P ratio increased linearly with time, whereas the enzyme C:N ratio lessened at the early stage and then grew at the late stage. Soil organic carbon, TN, and microbial biomass primarily controlled the variations in EEAs, and heavy metal contamination and SOC dominated the enzyme C:P ratio. Soil organic carbon and TN substantially regulated the variations in the enzyme C:N ratio at the early stage, and heavy metal contamination modulated the changes in the enzyme C:N ratio at the late stage. Conclusions: The present study suggests the potential N and P co-limitations in soils, which were essentially caused by the low P and N availabilities at the early stage of restoration. Meanwhile, we also highlight the significance of treating soil heavy metal contaminations to reduce the limitation of microbial C metabolism at the late stage. [ABSTRACT FROM AUTHOR]

Soil heterotrophic microorganisms play crucial roles in soil biogeochemical cycles by secreting extracellular enzymes, but their metabolism is often limited by resource availability. Identifying major resources that limit soil microbial metabolism could help to create reasonable management practices for the maintenance of ecosystem function. Robinia pseudoacacia plantations perform crucial functions in reconstituting the ecological integrity of disturbed ecosystems; however, soil microbial metabolic limitations in R. pseudoacacia plantations remain poorly understood. Herein, R. pseudoacacia plantations of four age classes (10, 22, 37, and 47 years old) were sampled in the loess hilly‐gully region of northern Shaanxi Province in China. This study analyzed the effects of stand age on soil extracellular enzyme activities and soil microbial metabolic limitation. It also determined the main factor driving soil microbial metabolic limitation and extracellular enzyme activities. The results of ecoenzymatic stoichiometry showed that nitrogen (N) limited soil microbial metabolism in R. pseudoacacia plantations. Soil microbial metabolism at 10 and 22 years old were more carbon (C)‐ and N‐limited than that at 37 and 47 years old. Except for N‐ and phosphorus (P)‐acquiring enzyme activities at 10–20 cm, soil C‐, N‐, and P‐acquiring enzyme activities (in 0–10 and 10–20 cm of soil) at 10 and 22 years old were significantly higher than those at 37 and 47 years old. The enzymatic ratio of C:N:phosphorus(P) acquisition in all R. pseudoacacia plantations, regardless of stand age and soil depth, deviated from 1:1:1. Soil nutrients explained most of the variation (90.80%) in soil extracellular enzyme activities based on variation‐partitioning analysis. The partial least squares path model showed that soil nutrients had the highest total negative effect on microbial C limitation and microbial N/P limitation. Our results confirmed that microbial metabolic limitation was induced by soil resource deficits. The findings provide another visual that increases our understanding of soil microbial metabolic limitation in R. pseudoacacia plantations. [ABSTRACT FROM AUTHOR]

Long‐term straw mulching was known to change soil nutrient content, aggregate distribution and extracellular enzyme activities. However, the impact of long‐term straw mulching on microbial nutrient limitations and carbon‐use efficiency (CUEst) within aggregates remains unclear. To fill the gap, we conducted a 10‐year field experiment in a semi‐arid region and used an ecoenzymatic stoichiometry model to quantify microbial resource limitations in soil aggregates under long‐term mulching. We studied the effects of two mulching measures (plastic film mulching [FM] and straw mulching [SM], with no mulching as the control [CK]) on the nutrient content and limitations within aggregates. The results show that compared with FM, SM increased the proportion of aggregates to larger >2 mm and decreased the proportion of aggregates in the 2–0.25 mm classes. Additionally, FM resulted in carbon (C) and phosphorus (P) limitations in the soil, particularly in the >2 mm class, while SM alleviated these constraints. This effect was primarily attributed to the increase in soil organic carbon (SOC) and microbial biomass carbon content (Cm), especially the enhanced carbon content associated with larger aggregates (>2 mm) and the increased activities of carbon–nitrogen (C–N)‐acquiring enzymes. SM also resulted in high CUEst by influencing microbial P limitation. Random forest analysis indicates that soil abiotic factors, particularly SOC and total nitrogen (TN), were the main drivers of microbial resource limitations within the aggregates. These findings suggest that the mulching material determines the development of soil aggregates and resource allocation within these aggregates. Thus, the study provides valuable insights for formulating effective carbon management strategies in semi‐arid regions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Excess Na+ and high pH result in poor structures in Saline-Sodic soils, which reduces extracellular enzyme activity (EEA) and causes nutrient limitations. The application of manure improved the Physical-Chemical properties of soil and balanced the soil nutrient supply, which was reflected in the soil EEAs and stoichiometry. Five experimental treatments were designed according to the manure application duration as follows: manure application for 11 years (11a), 16 years (16a), 22 years (22a), and 27 years (27a) and a control treatment with no manure application (CK). The results of the redundancy analysis (RDA) showed that physical properties (mean weight diameter (MWD)) and EEA (β–glucosidase (BG)) significantly increased and bulk density (ρb) significantly decreased when the nutrient content increased. Additionally, soil pH, electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) significantly decreased after manure application. Based on stepwise multiple linear regression models (SMLR), total nitrogen (TN) was the dominant variable that significantly increased EEA, and the Mantel test showed that soil C:N significantly influenced enzyme stoichiometry. Furthermore, RDA showed that pH, soil C:N and TN were the main factors influencing EEAs and enzyme stoichiometry. Soil EEAs significantly increased with TN and decreased with pH and soil C:N, which affected enzyme stoichiometry. The enzyme stoichiometry increased from 1:2.1:1.2 and 1:2.7:1.5 to 1:1.7:1.2, and the vector angle (vector A) increased, which showed that the N limitation was relieved after the application of manure. The vector length (vector L) showed no significant difference in the C limitation at depths of 0–20 cm and significantly increased at depths of 20–40 cm. In conclusion, soil EEAs and stoichiometry improved with changes in TN and soil C:N, and pH decreased with changes in the soil structure after the application of manure, which accelerated the soil nutrient cycle and balanced the soil nutrient supply. [ABSTRACT FROM AUTHOR]

Soil enzyme activity and its stoichiometry are excellent representatives of soil microorganisms' response to changing conditions, and act as a good indicator of microbial energy and nutrient demands. However, how soil enzyme activity and microbial nutrient limitation will be modified by grassland degradation is not well understood, especially in the saline‐alkaline meadow. Here, we presented how soil enzyme activity and microbial nutrient limitation shifted along a well‐characterized gradient of salinized degraded grasslands (non‐degraded, moderately degraded, and severely degraded). Our results showed soil enzyme activity was the highest in moderately degraded grasslands, which was mainly regulated by soil bacterial diversity. Soil microbial community metabolism in alkali‐saline meadow grasslands was limited by both carbon and phosphorus. Microbial carbon limitation showed a hump‐shaped pattern along the grassland degradation gradient, while microbial phosphorus limitation showed a gradually decreasing trend. Soil bacterial diversity is a key regulator of soil microbial carbon limitation, but the structure of the soil bacterial and plant community determines microbial phosphorus limitation. Taken together, our findings, taken together, provide evidence that soil bacteria are direct drivers of soil enzyme activity and microbial nutrient limitation along a grassland degradation gradient with salinization and suggest that these changes are regulated by soil salinity. [ABSTRACT FROM AUTHOR]

Simple Summary: Crabs are advanced predators in aquatic ecosystems, and they can feed directly on plant litter. They can also indirectly regulate the decomposition of organic matter in the aquatic environment by influencing snail populations and the structure of the substrate microbial community through top-down effects. When the invasive organism channeled apple snail (Pomacea canaliculata) meets the native species Chinese mitten crab (Eriocheir sinensis), new interspecific relationships and food web structures are created. This is of great concern in the context of climate change. Aquatic litter decomposition is highly dependent on contributions and interactions at different trophic levels. The invasion of alien aquatic organisms like the channeled apple snail (Pomacea canaliculata) might lead to changes in the decomposition process through new species interactions in the invaded wetland. However, it is not clear how aquatic macroinvertebrate predators like the Chinese mitten crab (Eriocheir sinensis) will affect the nutrient cycle in freshwater ecosystems in the face of new benthic invasion. We used the litter bag method to explore the top-down effect of crabs on the freshwater nutrient cycle with the help of soil zymography (a technology previously used in terrestrial ecosystems). The results showed significant feeding effects of crabs and snails on lotus leaf litter and cotton strips. Crabs significantly inhibited the intake of lotus litter and cotton strips and the ability to transform the environment of snails by predation. Crabs promoted the decomposition of various litter substrates by affecting the microbial community structure in the sediment. These results suggest that arthropod predators increase the complexity of detrital food webs through direct and indirect interactions, and consequently have an important impact on the material cycle and stability of freshwater ecosystems. This top-down effect makes macrobenthos play a key role in the biological control and engineering construction of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

The status of plant and microbial nutrient limitation have profound impacts on ecosystem carbon cycle in permafrost areas, which store large amounts of carbon and experience pronounced climatic warming. Despite the long‐term standing paradigm assumes that cold ecosystems primarily have nitrogen deficiency, large‐scale empirical tests of microbial nutrient limitation are lacking. Here we assessed the potential microbial nutrient limitation across the Tibetan alpine permafrost region, using the combination of enzymatic and elemental stoichiometry, genes abundance and fertilization method. In contrast with the traditional view, the four independent approaches congruently detected widespread microbial nitrogen and phosphorus co‐limitation in both the surface soil and deep permafrost deposits, with stronger limitation in the topsoil. Further analysis revealed that soil resources stoichiometry and microbial community composition were the two best predictors of the magnitude of microbial nutrient limitation. High ratio of available soil carbon to nutrient and low fungal/bacterial ratio corresponded to strong microbial nutrient limitation. These findings suggest that warming‐induced enhancement in soil nutrient availability could stimulate microbial activity, and probably amplify soil carbon losses from permafrost areas. [ABSTRACT FROM AUTHOR]

Aims: The response of soil microbial metabolic limitation in forest ecosystems to various factors remains poorly understood. The purpose of the study was to reveal the characteristics of microbial metabolic limitation in soil at the regional scale and the possible influencing factors. Methods: The vector analysis of enzyme activities was used to study the relative soil microbial metabolic limitation characteristics of Quercus aquifolioides forest ecosystems along a mean annual precipitation gradient (MAP, 650 mm–1160 mm). Results: The enzyme activities as well as their partial stoichiometric ratios had negative linear relationships with MAP. Soil microbial metabolism of the study area was limited mainly by carbon (C) and phosphorus (P) and partially by C and nitrogen (N). The C limitation showed a trend of first increasing slightly and then decreasing significantly along the MAP gradient, while N/P limitation did not show an obvious trend. Relative limitation of microbial metabolism was related closely to soil pH and nutrients, where C limitation was affected by soil pH, climatic factors, soil nutrient characteristics and topographic factor, and N/P limitation was affected by soil pH, topographic factor, diameter at breast height of the trees (DBH) and soil nutrient characteristics. In addition, the linear relationship between soil organic matter (SOM) and N limitation was significant, and it was inferred that the degree of N limitation might affect the stability of SOM and C stocks. Conclusions: Microbial C limitation was regulated by MAP, and soil properties were important drivers of both C and N/P limitations. [ABSTRACT FROM AUTHOR]

Soil extracellular enzymes play an important role in ecosystem energy conversion and material cycling. Ecoenzymatic stoichiometry can reflect the relationship between the soil's microbial nutrient cycle and nutrient limitation. However, there have been few studies on the differences in ecoenzymatic stoichiometry and nutrient limitation between rhizosphere soil and bulk soil. This study examined soil nutrients and enzyme activities in rhizosphere soil and bulk soil in a Larix principis-rupprechtii plantation in north China. The results showed that the levels of soil organic carbon (C), total nitrogen (N), and available nutrients in the rhizosphere soil were significantly higher than those in the bulk soil, whereas the total potassium (TK) level was significantly lower. The soil C:N, C:P, and N:P ratios of the rhizosphere soil also exceeded those of the bulk soil. The acid phosphatase (ACP), urease (UE), and β-glucosidase (β-GC) activities in the rhizosphere soil exceeded those in the bulk soil, whereas the activities of N-acetyl-β-D-glucosidase (NAG), aminopeptidase (LAP), and nitrogenase (NA) were lower. The ratios of C, N, and P acquisition activities changed from 1:1.7:1 in the rhizosphere soil to 1:2:1 in the bulk soil. Redundancy analysis showed that the available K and soil water content in the rhizosphere soil were the most important soil factors affecting soil enzyme activities and ecoenzymatic stoichiometry; those in the bulk soil were soil N:P and soil water content. These results suggest that not all soil enzyme activities present rhizosphere effects and that bulk soil is more susceptible to N limitation in Larix principis-rupprechtii plantations. Plant roots play an important role in regulating soil nutrients and soil activities, and future studies should examine the underlying mechanisms in more detail. [ABSTRACT FROM AUTHOR]

Aims: Cropland revegetation is an effective measure to curb soil erosion on eroding hillslopes and increase farmers' income at depositional check dams. However, how soil microbial metabolic limitation responds to cropland revegetation in erosion and deposition landscapes remains poorly understood, which has substantial implications for carbon (C) retention and nutrient cycling in the eroding environment. Methods: We sampled 0–2 m soils in cropland and revegetated forest and grassland at upslopes and check dams in the hilly-gully region of the Loess Plateau, China. The activities of soil C-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes were analyzed. The improved enzyme vector model (V-T model) based on balance points was used to quantify microbial metabolic limitations based on ecoenzymatic stoichiometry. Results: Microorganisms suffered from no energy (C) limitation, but the relative microbial C limitation was greater in revegetated forest than in cropland. At upslopes, the revegetated forest was primarily limited by P, while the revegetated grassland and cropland were limited by N, which was indicated by the VTN/P limitation values of 4.35, -2.74, and − 1.87, respectively. Microbial P limitation was greater in deep soils of revegetated forest due to the assimilation of P by the root system. At check dams, land-use change had no significant influence on microbial N/P limitations owing to abundant soil C and nutrients and a wet environment. Conclusion: Concludingly, cropland revegetation had a weaker influence on microbial metabolic limitation at the lower-lying topography, which compensates for the current understanding of resource restrictions on microorganisms at slopes or flat areas. [ABSTRACT FROM AUTHOR]

The use of microbial metabolic limitation techniques has the potential to provide insights into carbon and nutrient cycling in an ecosystem under the influence of climate change. This study aimed to determine the characteristics and potential mechanisms of microbial metabolic limitation at the different growth stages of winter wheat (Triticum aestivum L.) in response to elevated CO2 concentrations, warming and drought. Winter wheat plants were grown in artificial climate chambers, and a set of treatments were employed, including two levels of CO2 concentration (400 and 800 μmol·mol−1), a temperature regime (the current ambient temperature and a temperature increase of 4 °C) and water conditions (80% and 60% of the field water capacity). The results showed that the soil microbes were mainly limited by C and P. Microbial C limitation significantly decreased by 26.7% and 36.9% at the jointing stage and significantly increased by 47.6% and 42.6% at the grain filling stage in response to elevated CO2 and warming, respectively. The microbial P limitation significantly decreased by 10.9–13.0% under elevated CO2 at the anthesis and grain filling stages, while it was not affected by warming. Both microbial C and P limitations were unaffected by drought. The growth stage, soil dissolved organic carbon (DOC) and available phosphorus (AP) were the key factors affecting microbial C limitation, and microbial P limitation was mainly affected by the soil microbial biomass carbon (MBC), phosphorus (MBP) and microbial C:P ratio. Thus, the soil microbial C and P limitations differed with growth stages and were primarily indirectly affected by the available nutrients in the soil and the properties of the microbial biomass, respectively. These findings are important for understanding the mechanisms underlying microbe-mediated C and nutrient cycles. Overall, this study provides guidance for soil nutrient management in an agroecosystem experiencing climate change. [ABSTRACT FROM AUTHOR]

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.

Microbial metabolism directly participates in soil nutrient recycling and ecosystem stability. Although the rhizosphere soil is one of the most active habitats, information on how microorganisms acquire nutrients based on ecoenzymatic stoichiometry is lacking, especially for major food crops under field conditions. Thus, this study aimed to explore the soil nutrient properties and microbial biomass concentrations as well as extracellular enzymatic activities and focused on carbon (C), nitrogen (N), and phosphorus (P) cycling of different crop types, including potato (Solanaceae), maize (cereal), soybean (Leguminosae), and buckwheat (Polygonaceae) in the arid area of northern Shaanxi, China. Microorganisms in the rhizosphere soil of four crops were subjected to relative C and N limitation tests based on ecoenzymatic activities. Among the crops, potato and soybean exhibited the maximum limitations. Linear regression analysis of soil nutrients, microorganisms (stoichiometric homeostasis), and threshold elemental ratio synthetically supported microbial metabolic limitations. This finding coincided with the highest and lowest microbial carbon use efficiencies in soybean (0.58) and potato (0.51), illustrating the distinguishing physiological responses of microbes. Partial least squares path modeling further confirmed that the soil microbial nutrient limitations were significantly regulated by soil nutrient properties and extracellular enzyme activities. Taken together, soil microbial metabolism in agricultural ecosystems was co‐limited by relative C and N regardless of the main food crop families in this region in China (northern Loess Plateau). These observations clarified the nutrient cycling driven by soil elemental stoichiometry at the root–soil interface in arid and oligotrophic ecosystems. [ABSTRACT FROM AUTHOR]

Chinese fir (Cunninghamia lanceolata) is a kind of evergreen coniferous tree species, the expansion of its pure forest area and multiple generations of continuous planting has led to a decline of stand quality and woodland fertility. To further investigate the relationship between leaf, litter, and soil stoichiometry, microbial community status, and microbial resource limitation of Chinese fir after continuous planting. We studied the C, N, and P stoichiometries of leaf, litter, and soil from successive rotations of Chinese fir plantations. In addition to this, soil microbial biomass C, N, and P, extracellular enzymes, as well as the soil microbial community composition, were determined. The continuous planting of Chinese fir significantly increased the leaf N and P contents and decreased the C content of litter, and the soil C:N and C:P ratios, thus leading to a soil stoichiometric imbalance. The continuous planting of Chinese fir plantations significantly increased the soil microbial biomass. Compared with the first-generation plantations, the N and P contents of the second- and third-generation plantations increased by 37.11%, 21.83% and 46.28%, 73.38%, respectively, thus alleviating the restriction of microbial N and P. Under continuous planting, the extracellular enzyme activities of N (NAG + LAP) and P (AP) were significantly decreased, and those of the second- and third-generation plantations were significantly decreased by 7.05%, 9.43% and 11.79%, 48.94%, respectively, compared with those of the first-generation plantations, resulting in an increase of 7.85 and 3.19% in carbon-use efficiency. The fungi:bacteria (F:B) ratio of the soil microbial community was elevated in successive plantations. The least squares pathway model (PLS-PM) indicated that the stoichiometric ratio of ecological enzymes had an indirect negative effect on CUE, and was the strongest predictor. This study showed that the successive plantation of Chinese fir resulted in a leaf, litter, and soil stoichiometric imbalance, further affecting community composition and resource limitation of soil microorganisms. [ABSTRACT FROM AUTHOR]

Organic fertilization in agroecosystems is an efficient fertilization management for sequestering carbon (C). Microbial metabolism affects C sequestration by influencing the rate of soil C mineralization, however, the responses of microbial metabolism limitation and soil respiration to different organic fertilizations remain unclear. Here, an experiment started from 1988 in a dry land of Northwest China was used to explore the mechanisms of C sequestration under five typical fertilization managements, namely no fertilization (CK), mineral nitrogen fertilizer (NF), wheat straw (WS), cattle manure (CM), and green manure (GM). The results indicated that the WS, CM, and GM treatments increased C sequestration rates by 28.3 %, 119.4 %, and 72.1 % in the 0–60 cm layer, compared with NF, whereas C sequestration efficiency was the greatest in the GM treatment. In addition, organic fertilization treatments increased the contents of soil nutrients across all the soil layers to varying degrees, and the activities of C, nitrogen (N), and phosphorus (P) -related enzyme in 0–60 cm soil layer also increased by 219.1∼236.9 %, 236.7∼774.5 %, and 2.5∼36.5 % compared with NF. Enzymatic stoichiometry indicated that the soil microbial metabolism across all soil layer was mainly limited by P. Organic fertilization alleviated the microbial P limitation and decreased the microbial metabolic quotient (qCO 2) in 0–20 cm soil layer. And GM treatment showed the lowest P limitation and qCO 2 in all soil layers. The partial least square path model demonstrated that microbial P limitation was the main driver affecting qCO 2. Alleviating the microbial P limitation decreased unnecessary C loss during microbial catabolism, converting more C to MBC, thereby increasing CUE and lowering qCO 2. In summary, green manuring is the most efficient practice to benefit C sequestration across all fertilization managements in this study. [Display omitted] • Long-term fertilization management resulted in microbial P limitation across all soil layers. • Green manuring exhibited the lowest microbial P limitation in all soil layers. • Green manuring got the greatest carbon sequestration efficiency across all organic fertilization management. • P limitation was the main driver affecting qCO 2 and microbial C use efficiency. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is a key component of the carbon (C) cycle, and its accumulation is influenced by the stoichiometry of C: nitrogen (N): phosphorus (P), as well as microbial metabolism. However, the mechanisms driving SOC accumulation in agricultural and natural soils remain unclear. Therefore, this study aimed to investigate the impact of soil and microbial biomass (MB) C:N:P stoichiometry and microbial metabolic limitation on SOC accumulation in agricultural and natural soils. A survey of soils from 277 locations in eastern China was conducted, revealing that agricultural soils (paddy and upland soils) had 1.74-times higher SOC content than that of natural soils (wasteland and woodland soils). SOC showed a significant positive correlation with microbial C use efficiency (CUE), which in turn promoted SOC accumulation in agricultural soils. CUE was higher in agricultural soils (0.38–0.41) than in natural soils (0.25–0.31), which was attributed to reduced microbial metabolic limitation in agricultural soils. Increased nutrient supply was evident in agricultural soils, indicated by high SOC:TP, dissolved organic C:dissolved organic N, MBC:MBN, and MBC:MBP ratios, which alleviated microbial C and P limitations. However, in natural soils, low nutrient availability and enzyme activities resulted in significant microbial C and P limitations, thereby hindering SOC accumulation. Our results indicate that microbial metabolic limitation regulated by C:N:P stoichiometry stimulates SOC accumulation in agricultural soils, offering novel insights into SOC storage and emphasizing the importance of ecological stoichiometry and microbial metabolic limitation in SOC storage. [Display omitted] • Agricultural soils store more soil organic carbon than natural soils. • Carbon use efficiency was positively correlated with soil organic carbon. • Microbial C and P limitations negatively affected carbon use efficiency. • Decrease of the C:N:P stoichiometric ratios increased carbon use efficiency. [ABSTRACT FROM AUTHOR]

Excess Na+ and high pH result in poor structures in Saline-Sodic soils, which reduces extracellular enzyme activity (EEA) and causes nutrient limitations. The application of manure improved the Physical-Chemical properties of soil and balanced the soil nutrient supply, which was reflected in the soil EEAs and stoichiometry. Five experimental treatments were designed according to the manure application duration as follows: manure application for 11 years (11a), 16 years (16a), 22 years (22a), and 27 years (27a) and a control treatment with no manure application (CK). The results of the redundancy analysis (RDA) showed that physical properties (mean weight diameter (MWD)) and EEA (β–glucosidase (BG)) significantly increased and bulk density (ρb) significantly decreased when the nutrient content increased. Additionally, soil pH, electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) significantly decreased after manure application. Based on stepwise multiple linear regression models (SMLR), total nitrogen (TN) was the dominant variable that significantly increased EEA, and the Mantel test showed that soil C:N significantly influenced enzyme stoichiometry. Furthermore, RDA showed that pH, soil C:N and TN were the main factors influencing EEAs and enzyme stoichiometry. Soil EEAs significantly increased with TN and decreased with pH and soil C:N, which affected enzyme stoichiometry. The enzyme stoichiometry increased from 1:2.1:1.2 and 1:2.7:1.5 to 1:1.7:1.2, and the vector angle (vector A) increased, which showed that the N limitation was relieved after the application of manure. The vector length (vector L) showed no significant difference in the C limitation at depths of 0–20 cm and significantly increased at depths of 20–40 cm. In conclusion, soil EEAs and stoichiometry improved with changes in TN and soil C:N, and pH decreased with changes in the soil structure after the application of manure, which accelerated the soil nutrient cycle and balanced the soil nutrient supply.

Resource demand by soil microorganisms critically influences microbial metabolism and then influences ecosystem resilience and multifunctionality. The ecological remediation of abandoned tailings is a topic of broad interest, yet our understanding of microbial metabolic status in restored soils, particularly at the aggregate scale, remains limited. This study investigated microbial resources within soil aggregates from revegetated tailings and applied a vector model of ecoenzymatic stoichiometry to examine how different vegetation patterns (grassland, forest, or bare land control) impact microbial resource limitation. Five-year vegetation restoration significantly elevated carbon (C) and nitrogen (N) concentrations and their stoichiometric ratios in soil aggregates (approximately 2-fold), although these increases were not translated to in the microbial biomass and its stoichiometry. The activities of C- and phosphorus (P)-acquiring extracellular enzymes in these aggregates increased substantially postvegetation, with the most pronounced escalation in macroaggregates (>0.25 mm). The vector model results indicated soil microbial metabolism was colimited by C and P, most acutely in microaggregates (<0.25 mm). This colimitation was exacerbated by monotypic vegetation cover but mitigated under diversified vegetation cover. Soil nutrient stoichiometric ratios in vegetation restoration controlled microbial resource limitation, overshadowing the impact of heavy metals. Our findings underscore that optimizing resource allocation within soil aggregates through strategic revegetation can enhance microbial metabolism in tailings, which advocates for the implementation of diverse vegetation covers as a viable strategy to improve the ecological development of degraded landscapes.

Soil microbial resource limitation is an important indicator of the ecosystem function and process, especially the response mechanism of the ecosystem under global change. Known as an oasis in the degraded karst landscape, the microbial resource limitations of the karst tiankeng ecosystem are still unclear. In this study, the soil extracellular enzyme activities (EEAs) and stoichiometry (EES) related to carbon (C), nitrogen (N), and phosphorus (P) acquisition were assayed in karst tiankeng. Soil samples were collected from the sunny slope of tiankeng (TSU), the shady slope of tiankeng (TSH), the base of tiankeng (TB), and outside tiankeng (OT). The results showed that the soil enzymatic acquisition of C: N: P in karst tiankeng was deviated by 1: 1: 1, indicating that the stoichiometry of soil enzymes in karst tiankeng was in an unstable state. Soil microbial communities in karst tiankeng were limited by soil C and P, which were mainly achieved by altering soil nutrient stoichiometry. At the TSH site, soil microbes were minimally limited by C and P. The P-limitation was more evident outside karst tiankeng than inside karst tiankeng. These results showed that the unique habitat of karst tiankeng can alleviate microbial community P-limitation in karst land. This study highlights the characteristics of karst tiankeng ecosystems and their role in maintaining microbial survival and ecological function in karst fragile ecosystems.

Clarifying the soil microbial metabolism and resource limitations could help to understand the functions and processes of aboveground ecosystems, as well as to predict ecosystem stability under global climate change. Karst tiankeng is a kind of large-scale negative surface terrain on the surface which is similar to an oasis in degraded karst landscapes, but their soil microbial resource limitations still unclear. In this study, we evaluated and compared the soil microbial resource limitation in non-degraded tiankeng (NDT), moderately degraded tiankeng (MDT), heavily degraded tiankeng (HDT), and outside tiankeng (OT) by calculating soil ecoenzymatic stoichiometry. Overall, soil microbial communities were more limited by C and P in karst tiankeng ecosystem. The soil microbial C and P limitations significantly differed with the karst tiankeng degradation increased, and the lowest C and P limitations were observed in NDT. The higher microbial C and P limitations were observed in OT. Linear regression and redundancy analysis indicated that soil microbial C and P limitations were significantly influenced by soil nutrients. Karst tiankeng degradation influence the biogeochemical cycle and function of karst tiankeng systems. Our results highlight that karst tiankeng (especially the NDT) can provide a stable habitat for the survival of microorganisms in karst areas. Karst tiankeng is essential for regional ecological restoration and biodiversity conservation.

Aquatic litter decomposition is highly dependent on contributions and interactions at different trophic levels. The invasion of alien aquatic organisms like the channeled apple snail (Pomacea canaliculata) might lead to changes in the decomposition process through new species interactions in the invaded wetland. However, it is not clear how aquatic macroinvertebrate predators like the Chinese mitten crab (Eriocheir sinensis) will affect the nutrient cycle in freshwater ecosystems in the face of new benthic invasion. We used the litter bag method to explore the top-down effect of crabs on the freshwater nutrient cycle with the help of soil zymography (a technology previously used in terrestrial ecosystems). The results showed significant feeding effects of crabs and snails on lotus leaf litter and cotton strips. Crabs significantly inhibited the intake of lotus litter and cotton strips and the ability to transform the environment of snails by predation. Crabs promoted the decomposition of various litter substrates by affecting the microbial community structure in the sediment. These results suggest that arthropod predators increase the complexity of detrital food webs through direct and indirect interactions, and consequently have an important impact on the material cycle and stability of freshwater ecosystems. This top-down effect makes macrobenthos play a key role in the biological control and engineering construction of freshwater ecosystems.

Soil salinity affects the microbial carbon use efficiency (CUE) that in turn regulates soil‐atmosphere gas exchange and soil C sequestration. So far, little is known about CUE in salt‐affected soils. Hereby, CUE across coastal soils with electric conductivity (EC) ranging from 0.14 dS m−1 to 13.65 dS m−1 was investigated using stoichiometric modeling. Contrary to the belief that CUE decreases with salinity increase, this present study showed that CUE follows a unimodal pattern along the saline gradient with the highest CUE observed at EC = 2 dS m−1. When EC > 2 dS m−1, both CUE and soil microbial growth rate significantly decrease with salinity indicating that microorganisms sacrifice growth for survival/adaptation to high salt stress. When EC < 2 dS m−1, CUE shows a significant positive correlation with EC, but microbial community growth rates remain stable. We also observed that microbial growth becomes limited by carbon scarcity and that the degree of carbon constraint is significantly aggravated with EC. This implies that elevating CUE can be the preferred mechanism for microorganisms to stabilize elemental stoichiometry and maintain growth rate. Our results revealed that along the saline gradient, the dominant factor of CUE shifted from the ecological stoichiometry to salinity, which provides an insight into the microbial‐driven carbon cycling in salt‐affected soils. Plain Language Summary: Soil salinity affects the microbial carbon use efficiency (CUE), and thus affects carbon flow between soil and atmosphere. So far, little is known about CUE in salt‐affected soils. Hereby, CUE across coastal soils with electric conductivity (EC) ranging from 0.14 to 13.65 dS m−1 was investigated in this study. Contrary to the belief that CUE decreases with salinity increase, this present study showed two different patterns of CUE along the salinity gradient. When EC > 2 dS m−1, both CUE and soil microbial growth rate significantly decrease with salinity indicating that microorganisms sacrifice growth for survival/adaptation to high salt stress. When EC < 2 dS m−1, CUE shows a significant positive correlation with EC, but microbial community growth rates remain stable. We also observed that microbial growth becomes limited by carbon scarcity and that the degree of carbon constraint is significantly aggravated with EC. This implies that elevating CUE can be the preferred mechanism for microorganisms to stabilize their own C/N ratio and maintain growth rate. Our results revealed that along the saline gradient, the dominant factor of CUE shifted from the environmental element supply to salinity, which provides an insight into the microbial‐driven carbon cycling in salt‐affected soils. Key Points: Microbial carbon use efficiency (CUE) follows a unimodal pattern along the saline gradient with the highest value observed at EC = 2 dS m−1When EC > 2 dS m−1, microorganisms sacrifice growth for survival under salt stress resulting in the decrease of CUEWhen EC < 2 dS m−1, the elevated CUE is the main regulation for microorganisms to mitigate carbon restriction [ABSTRACT FROM AUTHOR]

Abstract Background Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies. Although soil pH has long been considered an essential driver of microbial growth and community composition, little is known about how soil acidification affects microbial acquisition and utilization of carbon (C) and nitrogen (N). To close the knowledge gap, we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur (S) to the soil in a meadow steppe. Results We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria (F:B) and microbial biomass C to N (MBC:MBN) and subsequently decreased the C:N imbalance between microbial biomass and their resources. The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation. To cope with enhanced C versus N limitation, soil microbial communities regulated the relative production of enzymes by increasing the ratio of β-glucosidase (BG, C-acquiring enzyme) to leucine aminopeptidase (LAP, N-acquiring enzyme), even though both enzymatic activities decreased with S addition. Structural equation modeling (SEM) suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency (CUE), which counteracted the negative effect of metal stress (i.e., aluminum and manganese) under soil acidification. Conclusions Overall, these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification, which may help predict soil microbial responses to future acid deposition.

Postfire regeneration is essential for maintaining the stability and functionality of forest ecosystems following wildfires. However, it is unclear whether regeneration patterns affect carbon (C), nitrogen (N), or phosphorus (P) limitations on microbial metabolism in the soil. In this study, we investigated the soil extracellular enzyme activities (EEAs) in different forest types regenerated by five patterns (Dahurian larch monocultures, Dahurian larch and birch mixed plantations, Mongolian pine monocultures, Mongolian pine and birch mixed plantations, and naturally regenerated forests). Based on the principles of ecoenzymatic stoichiometry, we elucidated the spatiotemporal variation in energy (C) and nutrient (N or P) limitations on soil microbial metabolism by collecting a total of 135 composite soil samples across three seasons in the five regeneration patterns. The regeneration pattern had a significant effect on the activities of C-, N- and P-acquiring soil extracellular enzymes (P <0.05). The P-acquiring enzyme activity was 2.71 times greater than the C-acquiring enzyme activity and 3.44 times greater than the N-acquiring enzyme activity across all forest types and seasons. The activities of microbial metabolic C-, N-, and P-acquiring enzymes showed similar seasonal dynamic patterns, with the exception of L-leucine aminopeptidase. In all forest types, the activities of enzymes responsible for acquiring C, N, and P were linearly correlated with one another according to the findings from standard major axis regression analysis (P <0.001). The values of the enzymatic vectors were greater than 45°, indicating that P rather than N was the dominant constraint on soil microbial metabolism. Forests with mixed regeneration patterns had greater P limitations than did the corresponding monoculture forests. Soil temperature was the common soil variable affecting the activities of EEAs across seasons, while the contents of soil organic carbon, dissolved carbon, ammonium nitrogen, and nitrate nitrogen were the significant driving factors of EEAs in a single season. However, forest productivity, including tree density, stand basal area, and forest stand volume had a predominant influence on microbial metabolic P limitation. This study suggests a pronounced role of P in soil microbial metabolism within boreal forests regenerated after wildfires. [Display omitted] • Artificial regeneration boosts forest productivity over natural regeneration. • The activities of all enzymes except for LAP show similar seasonal variations. • P rather than N is the dominant limitation nutrient of microbial metabolism. • Mixed-species plantations show greater microbial P limitation than monocultures. • Forest productivity has a key influence on microbial metabolic P limitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Long-term cover crops improved soil health index and multi-nutrient cycling. • Microbes were more limited by P in the surface soil, but more limited by C in the subsurface soil. • Microbial C limitation in the subsurface soil under cover crops is relatively weakened. • Nutrients drive soil health and multi-nutrient cycling by influencing microbial resource limitation. Cover crops are an increasingly important component of sustainable agriculture, as they can improve soil quality and productivity. However, how cover crops affect soil health and multi-nutrient cycling is not well understood. To address these issues, here, we established a long-term (15-year) field experiment to evaluate the influence of several cover crop treatments (legumes vs. non-legumes vs. mixture crop (legumes + non-legumes)) in a Carya cathayensis plantation on soils. We found that cover crops greatly increased both the soil health index and multi-nutrient cycling in both surface soil (0–20 cm) and subsurface soil (20–40 cm), especially in the mixed cover crop treatment, by enhancing several soil biochemical properties. In addition, cover crops lead to higher carbon (C), nitrogen (N), and phosphorus (P) acquisition enzyme activities. Enzyme stoichiometry analyses showed that microbial activity in the surface soil was mainly P-limited, whereas C-limitation was more pronounced in the subsurface soil. The reduction of C limitation in the cover crops subsurface soil contributes to microbial C turnover, potentially increasing soil C sequestration. Importantly, we found that soil health index was positively correlated with multi-nutrient cycling regardless of soil depth. However, increased microbial metabolic limitation in the subsurface soil detrimental to the maintenance of soil health and multi-nutrient cycling. Furthermore, soil nutrients regulate soil health index and multi-nutrient cycling by influencing microbial resource limitation. Overall, our study illustrates that the use of cover crops, especially cover crop mixtures in the long term can foster soil health and contribute to improved soil multi-nutrient cycling, and can be used as an effective sustainable agricultural management practices. [ABSTRACT FROM AUTHOR]

Summer drought conditions generally coincide with exposure to high ground-level concentrations of ozone (O 3). 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 O 3 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 O 3 treatments (charcoal-filtered air or ambient air +40 ppb of O 3). 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 O 3 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 O 3 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 O 3 -polluted and drought-exposed ecosystems. • Soil microbes were limited by P availability in this alkaline soil. • Drought stress was the main factor affecting soil enzymes and multifunctionality. • Drought-induced the reduction in soil moisture led to microbial P limitation. • Drought-induced the reduction in soil pH alleviated microbial P limitation. • Elevated O 3 effects failed to affect soil microbial nutrient limitation. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) can form a beneficial symbiotic relationship with shrubs, thereby playing a crucial role in enhancing the stability and sustainability of fragile arid and semiarid ecosystems. How will soil microbial metabolism change from monoculture to the mixed planting of shrubs? What regulatory role will AMF play in this process? Monoculture and mixed planting of three native shrubs were carried out, and treatments with and without AMF inoculation were established at the same time. The indicators of soil microorganisms, extracellular enzymes and nutrients were measured. The variations in ecoenzymatic stoichiometries, microbial nutrient limitations and regulatory factors were also analyzed. The ratio of soil microbial biomass C to N decreased significantly from the monoculture to the mixed planting of shrubs. The ratios of C- and P-acquiring enzymes and N- and P-acquiring enzymes increased in the mixed planting treatment. The microbial P limitation in the monoculture treatment was replaced by microbial N limitation in the mixed planting treatment, and the soil microbial C limitation increased in the mixed planting treatment. AMF inoculation mainly regulated the ecoenzymatic stoichiometric ratios and microbial nutrient limitations in the monoculture treatment but had little effect on the mixed planting treatment. The main factors influencing microbial C limitation were shrub species and AMF richness in the monoculture and mixed planting treatments, respectively. Soil available nutrients and AMF richness and diversity were identified as the main factors influencing microbial P limitation in the monoculture treatment compared with microbial N limitation in the mixed planting treatment. AMF inoculation and the mixed planting of shrubs effectively promoted soil nutrient cycling, which is highly important for restoring arid and semiarid vegetation. [ABSTRACT FROM AUTHOR]

Efficient remediation of soil contaminated by polycyclic aromatic hydrocarbons (PAHs) is challenging. To determine whether soil ecoenzyme stoichiometry influences PAH degradation under biostimulation and bioaugmentation, this study initially characterized soil ecoenzyme stoichiometry via a PAH degradation experiment and subsequently designed a validation experiment to answer this question. The results showed that inoculation of PAH degradation consortia ZY-PHE plus vanillate efficiently degraded phenanthrene with a K value of 0.471 (depending on first-order kinetics), followed by treatment with ZY-PHE and control. Ecoenzyme stoichiometry data revealed that the EEA C:N , vector length and angle increased before day five and decreased during the degradation process. In contrast, EEA N:P decreased and then increased. These results indicated that the rapid PAH degradation period induced more C limitation and organic P mineralization. Correlation analysis indicated that the degradation rate K was negatively correlated with vector length, EEA C:P , and EEA N:P , suggesting that C limitation and relatively less efficient P mineralization could inhibit biodegradation. Therefore, incorporating liable carbon and acid phosphatase or soluble P promoted PAH degradation in soils with ZY-PHE. This study provides novel insights into the relationship between soil ecoenzyme stoichiometry and PAH degradation. It is suggested that soil ecoenzyme stoichiometry be evaluated before designing bioremeiation stragtegies for PAH contanminated soils. [Display omitted] • Microbial mediated soil PAHs biodegradation is a coupled with the dynamic ecoenzyme stoichiometry. • Initial degradation period induces C and P limitations. • PAH degradation negatively links to C limitation. • Relative higher phosphatase activity benefits PAH degradation. [ABSTRACT FROM AUTHOR]

Tropical mountain ecosystems are usually colonized by numerous invasive plant species and represent an ideal 'natural laboratory' to study the effects of altitude on plant invasion. The aim of this study was to investigate the soil chemical and microbiological properties along an altitudinal gradient on a mountain colonized by the invader Ageratina adenophora. Rhizosphere soil of A. adenophora was collected over an altitudinal gradient (1400–2400 m) in Ailao Shan, China. We determined soil organic carbon (C), nutrient contents, enzyme activities, bacterial community composition as well as C and nitrogen (N) contents of the plant roots. Ecoenzymatic stoichiometric indices were calculated to estimate the relative C, N or P limitations of the microbial community. There was a significant effect of altitude on soil organic C in the rhizosphere, and a turning point in these measured variables was detected at an altitude of 2000 m. At low elevations, the rapid growth of invasive plants depleted the deficient phosphorus (P) in tropical soils, leading to microbial P limitation; at high elevations, microbes invested more energy to obtain C from resistant litter, leading to microbial C limitation. Bacterial beta diversity and soil pH contributed most to the altitudinal differences in ecoenzymatic stoichiometry, and Proteobacteria and Acidobacteria were the dominant bacterial phyla that determined the nutrient uptake status of microorganisms. These results demonstrate how microbial nutrient acquisition belowground of A. adenophora along an altitudinal gradient, which could contribute to further knowledge about the effects of altitude on biological invasion. [ABSTRACT FROM AUTHOR]

Soil enzyme activity and its stoichiometric ratio are important indicators reflecting soil nutrient availability and microbial growth and metabolic nutrient requirements. However, the effects of nitrogen-fixing tree species on soil aggregate-associated enzyme activities and ecoenzymatic stoichiometric characteristics in Eucalyptus plantations are still unclear. In this study, an 11-year-old pure E. urophylla plantation(PP)and an 11-year-old mixed E. urophylla and Dalbergia odorifera plantation(MP)in the Shaoping Experimental Field of the Tropical Forestry Experimental Centre of Chinese Academy of Forestry were selected as the research objects. Soil aggregates which were collected from 0-10 cm soil layer were classified into >2 mm, 1-2 mm, 0.25-1 mm, and <0.25 mm fractions by the improved dry-sieving procedure. And then the soil physicochemical properties and the activities of hydrolase [β -glucosidase(BG), N-acetyl-glucosidase(NAG), leucine aminopeptidase(LAP)and acid phosphatase(ACP)] related to soil carbon(C), nitrogen(N)and phosphorus(P)cycling in soil aggregates were measured and the effects of mixing nitrogen-fixing tree species with Eucalyptus on soil enzyme activities and its stoichiometry were examined. The results were as follows:(1)The dominant soil aggregates were >2 mm fractions which were higher than other aggregates. The contents of SOC, TN, NO3--N, AP, pH and activities of BG, NAG, ACP were significantly increased on each aggregate fractions except for LAP, respectively, in MP than in PP.(2)pH, TN, AP, NO3--N, NH4+-N had significant correlation with the ecoenzymatic stoichiometry. The redundancy analysis(RDA)found that the contents of NO3--N, SOC, and AP were key factors affecting the soil hydrolase enzyme activities and its stoichiometry.(3)The ecoenzymatic stoichiometry of C, N, P in this area was 1:0.86:0.74 [deviated from the global pattern(1:1:1)] which indicated that the soil microorganisms in this area were easily limited by C source. The C:N and C:P ratio of enzyme stoichiometric in most of the soil aggregates in MP were lower than those in PP, and significant differences were found in <0.25 mm fractions(P<0.05). Our findings suggest that the introduction of nitrogen-fixing tree species into eucalyptus plantations can not only alleviate the C source limitation of soil microbial growth and metabolism, but also effectively alleviate the N and P limitation of soil in this region. Findings from this study provide a scientific basis for the application of nitrogen-fixing tree species in improving soil quality and productivity of eucalyptus plantations. [ABSTRACT FROM AUTHOR]

Purpose: The presence and interaction of shrubs and arbuscular mycorrhizal fungi (AMF) are important for the biogeochemical cycles and sustainable development of arid and semiarid ecosystems. The regulatory mechanisms of the soil microenvironment were explored by studying microbial nutrient constraints in ecosystems. Materials and methods: Three native shrubs were planted with and without AMF inoculation in the experimental nursery of Inner Mongolia Agricultural University. The soil chemical properties; enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) acquisition; and microbial biomass C and N were measured to determine the ecoenzymatic stoichiometries and microbial nutrient limitations of the rhizosphere soils. Results: The ratios of ecoenzymes associated with C acquisition in the rhizospheres of Spiraea pubescens were the largest, as well as microbial C limitation. In addition, Clematis fruticosa and Amygdalus mongolica inoculated with AMF significantly increased the ratios of enzymes related to C acquisition and increased microbial C limitation in the rhizospheres of these two shrubs. The ratio of N and P acquisition enzymes showed that A. mongolica and S. pubescens were significantly lower than C. fruticosa, and the lowest microbial P limitation was found in the rhizosphere soil of C. fruticosa in the noninoculated treatment; however, there was no significant difference between shrubs in the inoculated treatment. The microbial P limitation of the shrubs with AMF inoculation could be positive, negative, or not impacted. This result indicated that AMF regulated microbial P limitation in the rhizospheres of shrubs and was closely related to the accumulation of plant biomass. Partial least squares path model analysis indicated that the main influencing factors of microbial C and P limitation were glomalin-related soil protein (GRSP) and soil available nutrients (SANU). Conclusions: The results indicated that shrubs and AMF altered the ecoenzymatic stoichiometry of the rhizosphere soils, thus affecting soil microbial nutrient limitation through GRSP and SANU. Native shrubs with AMF inoculation can regulate soil microbial metabolism, providing a theoretical basis for vegetation restoration of degraded ecosystems in drylands. [ABSTRACT FROM AUTHOR]

Purpose: Variation in soil microbial metabolism remains highly uncertain in predicting soil carbon (C) sequestration, and is particularly and poorly understood in agroecosystem with high soil phosphorus (P) variability. Materials and methods: This study quantified metabolic limitation of microbes and their association with carbon use efficiency (CUE) via extracellular enzymatic stoichiometry and biogeochemical equilibrium models in field experiment employing five inorganic P gradients (0, 75, 150, 225, and 300 kg P ha−1) in farmland used to grow peas. Results and discussion: Results showed P fertilization significantly increased soil Olsen-P and NO3−-N contents, and enzyme activities (β-1,4-glucosidase and β-D-cellobiosidase) were significantly affected by P fertilization. It indicated that P fertilization significantly decreased microbial P limitation due to the increase of soil available P. Interestingly, P application also significantly decreased microbial nitrogen (N) limitation, a phenomenon primarily attributable to increasing NO3−-N content via increasing biological N fixation within the pea field. Furthermore, P fertilization increased microbial CUE because the reduction in microbial N and P limitation leads to higher C allocation to microbial growth. Partial least squares path modeling (PLS-PM) further revealed that the reduction of microbial metabolic limitation is conducive to soil C sequestration. Conclusions: Our study revealed that P application in agroecosystem can alleviate not only microbial P limitation but also N limitation, which further reduces soil C loss via increasing microbial CUE. This study provides important insight into better understanding the mechanisms whereby fertilization mediates soil C cycling driven by microbial metabolism in agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BACKGROUND: Soil‐ and plant‐produced extracellular enzymes drive nutrient cycling in soils and are assumed to regulate supply and demand for carbon (C) and nutrients within the soil. Thus, agriculture management decisions that alter the balance of plant and supplemental nutrients should directly alter extracellular enzyme activities (EEAs), and EEA stoichiometry in predictable ways. We used a 12‐year experiment that varyied three major continuous grain crops (wheat, soybean, and maize), each crossed with mineral fertilizer (WCF, SCF and MCF, respectively) or not fertilized (WC, SC and MC, respectively, as controls). In response, we measured the phospholipid fatty acids (PLFAs), EEAs and their stoichiometry to examine the changes to soil microbial nutrient demand under the continuous cropping of crops, which differed with respect to the input of plant litter and fertilizer. RESULTS: Fertilizer generally decreased soil microbial biomass and enzyme activity compared to non‐fertilized soil. According to enzyme stoichiometry, microbial nutrient demand was generally C‐ and phosphorus (P)‐limited, but not nitrogen (N)‐limited. However, the degree of microbial resource limitation differed among the three crops. The enzymatic C:N ratio was significantly lower by 13.3% and 26.8%, whereas the enzymatic N:P ratio was significantly higher by 9.9% and 42.4%, in MCF than in WCF and SCF, respectively. The abundances of arbuscular mycorrhizal fungi and aerobic PLFAs were significantly higher in MCF than in WCF and SCF. CONCLUSION: These findings are crucial for characterizing enzymatic activities and their stoichiometries that drive microbial metabolism with respect to understanding soil nutrient cycles and environmental conditions and optimizing practices of agricultural management. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Aim: Ecoenzymatic stoichiometry provides a promising avenue for deciphering resource constraints on soil microbial metabolism but is hampered by limitations in current modelling techniques. Innovation: Herein we developed new models for quantifying microbial metabolic limitations based on the stoichiometric and metabolic theories of ecology, using an extensive database (n = 2,667) that revealed relationships far from the widely recognized mean ratio of 1:1:1 for carbon : nitrogen : phosphorus (C : N : P) acquiring enzyme activities. We estimated the balance points of P and N acquisition (x0, y0) in the absence of resource constraints to redefine the boundary between P versus N limitation. We then calculated two alternative boundary conditions defining P versus N limitation by scaling the classic threshold element ratio (TER), generating two new models (TEREEA and TERL). In addition, a new enzyme vector (V‐T) model was devised by correcting traditional vector calculations based on observed enzyme activities against these balance points. Main conclusions: These three new models more consistently predicted microbial metabolic limitations than the traditional TER and vector models. They also predicted that microbial metabolism in high‐latitude grasslands and low‐latitude forests were predominantly limited by soil N and P, respectively, and that increases in soil organic C with ecosystem development could intensify these limitations. In contrast, fertilizers alleviated these limitations in agricultural ecosystems, suggesting that widespread anthropogenic effects could potentially alter microbial resource limitations even in natural ecosystems. In addition, C limitation to microbial metabolism identified by the new V‐T model showed a consistent negative correlation with microbial C use efficiency among ecosystems, confirming that resource constraints regulate microbial resource allocation. These new models provide more precise predictions of microbial metabolic limitations across a wide range of ecosystems and thus may be useful tools for the study of microbial macroecology. [ABSTRACT FROM AUTHOR]

Tillage and straw incorporation are important agricultural practices that can break the plow layer and improve Mollisol fertility. The effect of these practices on the limitation of resources for soil microorganisms, however, is unclear. We established a field experiment in 2018 and collection of soil samples in 2020 to study the acquisition of resources by microbes in a Mollisol region in northeastern China. Four treatments were studied: conventional tillage (CT), straw incorporation with conventional tillage (SCT), subsoil tillage (ST) and straw incorporation with subsoil tillage (SST). The limitation of resources for soil microorganisms was assessed using models of extracellular enzymatic stoichiometry. The soil microbes were generally colimited by C and P but not N. The degree of limitation, however, varied among the treatments. SCT and SST alleviated microbial P limitation in the 0–15 and 15–35 cm layers, respectively, but ST did not significantly affect P limitation relative to CT. Interestingly, N-resource contents were strongly correlated with indicators of C and P limitation. A random forest analysis found that the contents of available N and total dissolved N were the most important factors for microbial C and P limitation, respectively. Straw incorporation alleviated microbial P limitation but did not eliminate P limitation and deep tillage aggravate microbial C limitation. We suggest that N fertilization may be reduced due to the N-rich characteristics of the Mollisols in northeastern China.

Aims: Invasive plants not only alter aboveground biodiversity but also belowground microbial community composition to facilitate their growth and competitiveness. However, how plant invasion affects soil microbial resource limitation and metabolic activity, and their linkages with litter and soil stoichiometries remain largely unknown. Methods: We investigated the carbon (C): nitrogen (N): phosphorus (P) stoichiometries of litter, soil, microbe and extracellular enzymes, composition of main microbial groups and substrate utilization rate in a subtropical forest invaded by Moso bamboo (Phyllostachys edulis) and those in adjacent broadleaf and mixed bamboo-broadleaf forests. Results: Bamboo invasion significantly decreased annual litter production, litter C: P and N: P ratios, and soil C:N and C:P ratios, whereas increased microbial biomass C:N and C:P ratios, resulting in decreased C:N and C:P imbalances between soil microorganisms and their resources. Bamboo invasion decreased the N and P acquiring enzymes activities, mitigated the status of microbial N and P limitation as indicated by enzymatic stoichiometry, and caused a higher C use efficiency. Soil microbial community structure was shifted towards a lower fungi: bacteria (F:B) ratio in bamboo forest. Bamboo forest soil showed a lower capacity of microbes to use N-rich resources in comparison to C-rich resources. Structural equation modeling suggested a direct and negative effect of C:N imbalance on microbial N limitation and metabolic capacity. Conclusions: This study suggests the importance of stoichiometric imbalance between decomposers and their resources in regulating soil microbial community structure and enzyme activities following plant invasion. [ABSTRACT FROM AUTHOR]

Straw return is a key method to regulate soil carbon (C) by microbial utilization accumulating and CO 2 releasing, which mainly depends on microbial metabolism processes. The present knowledge of the mode and mechanism of soil CO 2 emission under straw return is limited. We established four straw return treatments, including straw shallow return (SS, 0–20 cm), straw subsoil burial (SD, 20–40 cm), straw mulching (SM), and control with no straw (NS). Microbial metabolic limitation and the abundance of C degradation functional genes were quantified using enzyme stoichiometry and high-throughput quantitative PCR-based chip technology, respectively. The results revealed that the addition of straw inputs resulted in an increase in soil nutrient contents and soil CO 2 emissions. The cumulative CO 2 emissions of SS and SM treatments were 21,013.53 and 20,819.26 kg hm−2, respectively, which significantly increased by 4.70 % and 3.73 % compared with SD treatment. Compared with SM and SD treatments, microbial C and P limitations of SS treatment were significantly enhanced, increasing by 1.15 %–1.20 % and 2.73 %–1.21 %, respectively. Straw return increased the absolute abundance of genes engaged in decomposing diverse C source compounds, although with a reduction in microbial C use efficiency. The absolute abundance of amyA , apu , sga , abfA , xylA , and manB labile C degradation genes was higher in SM than in SD treatment, increasing by 1.11 %–25.88 %. On the contrary, the absolute abundance of glx and lig recalcitrant C degradation genes was lower in SM than in SD treatment, reducing by 2.96 %–3.68 %. Straw return directly impacts soil nutrient contents and indirectly influences microbial biomass carbon (MBC), nutrient limitation, and C degradation genes, as revealed by the partial least squares pathway model, ultimately leading to changes in soil CO 2 emissions. This finding should contribute to the enhancement of soil C retention and the selection of appropriate methods for straw incorporation in tillage fields. [Display omitted] • Microbial metabolism limitations induced changes in C degradation functional genes. • Straw subsoil burial decreased labile but increased recalcitrant genes abundance. • Soil CO 2 emissions increased with the increasing MBC and functional genes. • Straw subsoil burial had lower microbial metabolism limitations and CO 2 emissions. [ABSTRACT FROM AUTHOR]