Microbial Biomass Stoichiometry Research Articles

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

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

Linkage between soil stoichiometric imbalance and microbial carbon use efficiency in desert steppe under different grazing intensities.

Long-term grazing alters soil resource availability and microbial biomass stoichiometry in grassland ecosystems. Exploring the relationship between soil stoichiometric imbalance and microbial carbon use efficiency (CUE) in grazed desert steppe can help understand soil carbon dynamics from a microbial perspective. Based on a long-term grazing platform in Stipa breviflora desert steppe of Inner Mongolia established in 2004, taking heavy, moderate and light grazing intensities, using no grazing as a control, we measured soil available nutrients, microbial biomass and associated enzyme activities for their acquisition, and calculated soil microbial CUE using ecological stoichiometry. The results showed that grazing inhibited soil microbial CUE by 1.0%-10.3%. Soil C:N imbalance was significantly increased by 20.6% in the moderate grazing treatment, while both C:P imbalance and N:P imba-lance were significantly increased by 20.7% and 25.2% in the heavy grazing treatment, indicating that soil microbial communities were more susceptible to N and P limitation. Soil microbial communities maintained their stoichiometric balance by regulating the threshold of elemental stoichiometry ratios and the production of extracellular enzymes. Structural equation modelling (SEM) results indicated that stoichiometric imbalance indirectly affected microbial CUE by altering the threshold of elemental stoichiometry ratios, microbial biomass stoichiometry, and enzyme stoichiometry.

Response of soil microbial homeostasis to soil ecological stoichiometric balance in a World Natural Heritage area

Soil microbial biomass stoichiometry homeostasis is essential for microorganism survival and ecosystem stability. Despite its importance, research on soil microbial homeostasis in Natural World Heritage Sites (NWHS) is lacking. This study analyzed ecological stoichiometry and microbial homeostasis in surface (0–20 cm) and subsurface (20–40 cm) soils across various vegetation types in Fanjing Mountain, an NWHS in China. The objective was to explore microbial homeostasis in relation to soil ecological stoichiometry and identify key influencing factors. Results indicated that microbial biomass stoichiometry in surface soil is higher than in subsurface soil for 5 vegetation types, mirroring nutrient stoichiometry but contrasting enzyme stoichiometry. Vector length (VL) suggests higher C limitation in subsurface soil for all vegetation types, while vector angle (VA) shows P limitation in surface soil of certain types and N limitation in subsurface soil across all types. Random forest analysis revealed that the microbial carbon-nitrogen ratio (MB C/N) was mainly contributed by C/N (14.11 %), SOC (12.31 %), pH (10.52 %), NH4+-N, SWC, NO3--N in the surface soil, and NO3--N (15.74 %), altitude, SWC, SOC, C/N in the subsurface soil, whereas for the microbial carbon-phosphorus ratio (MB C/P), altitude (12.16 %), SWC (9.86 %), and AP were the main contributing factors in the surface soil, and in the subsurface soil, altitude (10.49 %), C/P, SWC, SOC, and TP. This study provides insights into ecological stoichiometry, homeostasis, and nutrient limitations in Fanjing Mountain, aiding vegetation nutrient balance management in NWHS.

Exploring polyphosphates in soil: presence, extractability, and contribution to microbial biomass phosphorus

Polyphosphates (Poly-P) are known to fulfil several important physiological functions. Many microorganisms can accumulate large amounts of Poly-P in their biomass. Regardless of these facts, systematic research on Poly-P in soil is missing, probably due to the absence of any method of direct Poly-P quantification. In this study, we attempted to unequivocally prove the presence of Poly-P in the biomass of soil microorganisms and quantify their extractability and contribution to microbial biomass phosphorus. To do so, we combined several approaches that can indicate Poly-P presence in soil microbial biomass indirectly, i.e. growth of soil inoculum on media without phosphorus, associated with measurement of changes in the microbial biomass stoichiometry, and the colour of the microbial suspension stained by the Neisser method. All soil microbial communities exhibited growth on media without phosphorus. As the growth on this media depleted Poly-P content, the biomass carbon to phosphorus and nitrogen to phosphorus ratio increased and the colour of the microbial suspension stained by the Neisser method changed predictively. The associated Poly-P addition experiment indicated that the recovery of added Poly-P from soil in form of soluble reactive phosphorus in sodium bicarbonate extract may reach up to 93% mainly due to abiotic depolymerization. Using a simple stoichiometric model applied to measured data, we calculated that the Poly-P content of microbial biomass in our soils may be up to 45 or 70% of total microbial biomass phosphorus depending on the assumptions applied regarding parameter values. We discuss the magnitude of error associated with the measurement of soil microbial phosphorus due to the high extractability of Poly-P.

Altered intra-annual precipitation patterns affect the N-limitation status of soil microorganisms in a semiarid alpine grassland

The ongoing intensification of the hydrological cycle due to global climate change alters intra-annual precipitation variability. Changes in precipitation patterns lead to disparities in soil moisture; however, the responses of soil extracellular enzyme activities (EEAs) and microbial metabolism limitations to them is unclear. This study conducted an in situ field experiment in the alpine grasslands of the Kunlun Mountains to simulate the same amount of precipitation but change the distribution time of precipitation within the plant growing season. We examined the effects of variability in intra-annual precipitation patterns on the stoichiometry of topsoil (0–5 and 5–20 cm) properties, microbial biomass, and EEAs. Results showed that altered precipitation patterns significantly increased soil moisture’s disparity index (D) by 57 %–89 %. The activity of nitrogen-acquiring enzymes (L-leucine aminopeptidase) was increased by 20.82–32.08 % (P < 0.05) with increased variability of precipitation, while phosphorus-acquiring enzymes (Acid phosphatase) and carbon-acquiring enzymes (β-glucosidase) both decrease by 9.25–23.35 % and by 17.86–33.04 %, respectively (P < 0.05). We determined that soil microorganisms in the study region were metabolism-limited by nitrogen (vector angles < 45◦), and increased precipitation variability exacerbated nitrogen limitation (decrescent vector angles) and alleviated carbon limitation (shortened vector length). In addition, soil EEAs can be both interactively influenced by biotic and abiotic factors, with abiotic factors (i.e., D, soil organic carbon content, and soil total nitrogen content) having a stronger effect. Our study provides an effective strategy for regulating soil EEAs, microbial biomass, and microbial metabolism limitation and contributes to developing nutrient management and restoration strategies in semiarid alpine grassland ecosystems.

Effect of nutrient management and soil type on stoichiometric imbalances across the Yangtze River Basin pear districts, China

AbstractNutrition management affects soil carbon (C), nitrogen (N), and phosphorus (P) cycles, as well as their stoichiometry, causing further stoichiometric imbalances. However, research on the effect of nutrient management on soil stoichiometric imbalance is restricted to a single soil type, limiting our understanding of the interactions between these parameters. Therefore, we conducted a study comprising 212 sites throughout the Yangtze River Basin pear districts, for which nutrient management and soil properties were available under different soil types. Soil stoichiometric imbalances varied widely among the districts, with an average C:P imbalance value (C:Pim) of 6.67, higher than that of C:N imbalance (C:Nim; 6.43) and N:P imbalance (N:Pim; 2.83). Meanwhile, soil and microbial biomass stoichiometry, particularly for soil C:P and soil microbial biomass carbon and phosphorus (MBC:MBP), were significantly influenced by nutrient addition. Large N and P fertilizer inputs altered soil C:N and C:P in yellow–brown earth, while soil C:P was influenced by organic nutrient management in purplish soil. Moreover, adding organic nutrients altered the MBP, which further influenced MBC:MBP and MBN:MBP in saline–alkaline soil and yellow–brown earth. Furthermore, C:Pim increased with increasing organic nutrient input in purple soil and decreased with a large chemical fertilizer input in red soil. N:Pim and C:Nim were weakly associated with nutrient management in different soil types. In addition, nutrition management, soil type, soil properties, and microbe content collectively accounted for 45%, 32%, and 38% of the C:Pim, C:Nim, and N:Pim variation, respectively. Nutrient management also exerted a positive direct impact on C:Pim, while soil type elicited a negative direct impact on C:Nim and N:Pim. Meanwhile, all three stoichiometric imbalances were indirectly influenced by soil type. Taken together, our results indicate that soil stoichiometric imbalances, especially for C:Pim, are sensitive to nutrient management and soil type, providing novel insights into these imbalances that can inform the development of potential remedial strategies.

Afforested and abandoned land ecosystems exhibit distinct soil microbial biomass stoichiometric homeostasis over chronosequence

AbstractRevegetation influences microbial biomass stoichiometry by altering the substrate conditions, yet the differences in microbial stoichiometry homeostasis and the underlying drivers under different revegetation approaches remain unexplored. Here, we selected sites across three age classes of Robinia pseudoacacia plantation (RP) and abandoned land (AL), and quantified the microbial stoichiometric characteristics during farmland‐initiated restoration. Plant community composition, leaf and soil nutrients, and microbial community composition and diversity were also measured. We found that revegetation of former farmland under both restoration types resulted in non‐isometric changes in soil carbon (C), nitrogen (N), and phosphorus (P) contents, that is, decoupling of soil C and N from P. However, AL and RP succession exhibited homeostatic and plastic microbial biomass stoichiometry, respectively, in response to altered substrate stoichiometry. These differences were associated with adjustments in the above‐ and belowground biomes. Specifically, the synergistic increase of Compositae and Actinobacteria in the late AL succession allowed the ecosystem to reduce P demand and maintain microbial stoichiometric homeostasis. In contrast, higher leaf C and N input during RP succession may have resulted excessive microbial storage of elements, which in turn leads to stoichiometric convergence between microbial biomass and soil resources. In addition, RP succession caused changes in microbial community structure, mainly the continuous increase of Proteobacteria (copiotrophs, r‐strategists), which also potentially increased the requirement for resources to maintain homeostasis and ensure the rapid growth. These findings demonstrate that AL has a comparatively greater efficacy in maintaining microbial stoichiometric homeostasis during long‐term revegetation. Our study also highlights the importance of appropriately managing existing RP plantations to alleviate the pressure of P deficiency and sustainably maintain this fragile ecosystem.

Soil and microbial C:N:P stoichiometries play vital roles in regulating P transformation in agricultural ecosystems: A review

Stoichiometry plays a crucial role in biogeochemical cycles and can modulate soil nutrient availability and functions. In agricultural ecosystems, phosphorus (P) fertilizers (organic or chemical) are often applied to achieve high crop yields. However, P is readily fixed by soil particles, leading to low P use efficiency. Therefore, understanding the role of carbon:nitrogen:P stoichiometries of soil and microorganisms in soil P transformation is of great significance for P management in agriculture. This paper provides a comprehensive review of the recent research on stoichiometry effect on soil P transformation in agricultural ecosystems. Soil microorganisms play an important role in the transformation of soil non-labile inorganic P to microbial biomass P by regulating microbial biomass stoichiometry. They also mobilize soil unavailable organic P into available P by changing ecoenzyme stoichiometry. Organic materials, such as manure and straw, play an important role in promoting the transformation of insoluble P into available P as well. Additionally, periphytic biofilms can reduce P loss from rice field ecosystems. Agricultural stoichiometries are different from those of natural ecosystems and thereby should receive more attention due to the influences of anthropogenic factors. Therefore, it is necessary to conduct further stoichiometry research on the soil biochemical mechanisms underlying P transformation in agricultural ecosystems. In conclusion, understanding stoichiometry impact on soil P transformation is crucial for P management in agricultural ecosystems.

Effects of Short-term Nitrogen Addition on Soil Organic Carbon Components in Robinia pseudoacacia L. Plantation

Nitrogen (N) deposition in the context of human activities continuously affects the carbon cycle of ecosystems. The effect of N deposition on soil organic carbon is related to the differential responses of different carbon fractions. To investigate the changes in soil organic carbon fraction and its influencing factors in the context of short-term N deposition, four N addition gradients:0 (CK), 1.5 (N1), 3 (N2), and 6 (N3) g·(m2·a)-1 were set up in acacia plantations based on field N addition experiments, and the soil physicochemical properties, microbial biomass, and enzyme activities were measured in June and September. The results showed that:① exogenous N input reduced soil pH, promoted the increase in soluble organic carbon content, and increased soil nitrogen effectiveness. ② Short-term N addition significantly reduced soil organic carbon content, and the response of each component of organic carbon to N addition was different. Among them, the content of easily oxidized organic carbon was significantly reduced and reached the lowest value under the N2 treatment, with 54.4% and 48.2% reduction compared with that of the control, respectively, and the content of inert organic carbon increased, although the increase was not significant. Nitrogen addition reduced the soil carbon pool activity and improved the stability of the soil carbon pool. Soil carbon pool activity reached its lowest under the N3 and N2 treatments, with a decrease of 53.3% and 52.80%, respectively, compared to that of the control. ③Random forest modeling indicated that the soil microbial biomass stoichiometry ratio, microbial biomass carbon, and AP were the key factors driving the changes in soil organic carbon activity under short-term N addition, explaining 65.96% and 66.68% of the changes in oxidizable organic carbon and inert organic carbon, respectively. Structural equation modeling validated the results of the random forest modeling, and soil microbial biomass stoichiometric ratios significantly influenced carbon pool activity. Short-term nitrogen addition changed soil microbial biomass and its stoichiometric ratio in the acacia plantation forest mainly through two pathways, i.e., increasing soil nitrogen effectiveness and promoting soil acidification and inhibiting extracellular carbon hydrolase activity, thus changing the soil carbon fraction ratio and participating in the soil organic carbon cycling process.

Effect of forest chronosequence on ecological stoichiometry and nitrogen and phosphorus stocks in Alnus nepalensis forest stands, central Himalaya

AbstractIn the mid and high elevations of the central Himalaya, Nepalese alder (Alnus nepalensis D. Don) occurs in areas affected by landslides/landslips and is a nitrogen‐fixing species; it quickly improves soil physical and chemical properties and facilitates the restoration of degraded forests. In the present study, we evaluated the effect of A. nepalensis forest chronosequence on the carbon (C), nitrogen (N), and phosphorus (P) concentrations, N and P stocks, and stoichiometry in the soil, including microbial biomass C (MBC), microbial biomass N (MBN) and microbial biomass P (MBP), and in the plant components. Six naturally occurring forest stands were identified in a chronosequence of A. nepalensis (age 3–270 years old) forest stands, namely alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The biomass of tree components was estimated using species‐specific allometric equations developed by previous workers for the region. Soil total N and total P stocks of each species were determined by the N and P concentrations and bulk density. Structural equation modeling (SEM) was performed to quantify the contribution of N and P pools to ecosystem nitrogen and phosphorus stocks. The results of this study revealed that the stoichiometry (C:N, N:P, and C:P ratios) of tree components (i.e., leaves, leaf litter, twig), soil and microbial biomass varied widely, and the presence of nitrogen‐fixing A. nepalensis in different succession stages significantly improved the soil and microbial biomass stoichiometry. Total vegetation (tree, herbs, shrubs, and litter) biomass N stock ranged from 346.77 to 4662.06 kg N ha−1, and soil N stock varied from 816.48 to 7334.24 kg N ha−1. Total ecosystem N and P stocks ranged from 1163.26 to 11,996.31 kg N ha−1 and 76.10 to 799.28 kg P ha−1, respectively, and positively increased with A. nepalensis total biomass. The soil P stock accounted for 63.49% to 74.80% of the total P stocks of the forest ecosystems. Overall, our findings suggest that A. nepalensis forest chronosequence enhanced the N and P stocks, and introducing this species in degraded forests appears to be an option for enhancing forest conservation and rehabilitation actions in the central Himalaya.

One-time freeze-thawing or carbon input events have long-term legacies in soil microbial communities

Soil microbial communities are regularly exposed to sudden changes in environmental conditions, such as root exudation pulses or freeze-thaw events. As microbial communities have a high potential to adapt to changing conditions, they are expected to be resilient towards this kind of short-term perturbations and return to their pre-perturbed state quickly. Here, we conducted a lab incubation experiment to evaluate the resilience of soil microbial communities to single-pulse perturbations.We incubated temperate forest soil at constant temperature (20 °C) and water content, and exposed it to strong single-pulse perturbations, which nonetheless mimic common pulse-events in temperate soils (glucose addition at 4 mg g−1 soil, or freeze-thawing overnight at −20 °C). We subsequently measured microbial community composition and microbial storage compounds via phospho- and neutral lipid fatty acid (PLFA and NLFA) profiling, as well as C/N stoichiometry of microbial biomass and dissolved organic carbon and nitrogen in the soil solution shortly after (0.4, 1, 4, and 6 days) and after longer time periods (84 and 160 days) following the perturbations.Transferring the soils from their natural environment to the laboratory and incubating them under controlled conditions led to a continuous change of microbial community structure over time, along with an increase in microbial biomass and dissolved N in both perturbed and control soils over the time of the experiment. Against the background of this ‘press-disturbance’, caused by the permanently changed conditions, we see immediate and long-lasting effects of the single pulse events on microbial community composition, C storage and C/N stoichiometry. Both perturbations significantly influenced the microbial community structure (based on PLFA profiles), microbial biomass N and dissolved N up to 160 days, as well as fungal and bacterial biomass and storage (based on absolute PLFA and NLFA concentrations) up to 84 days. Both perturbations increased microbial N (+59.6 µg g−1 dw) and decreased dissolved N (−40.3 µg g−1 dw) after 160 days, and significantly altered C/N ratios in microbial and dissolved pools (particularly in the first 6 days of the experiment).Our results demonstrate that single-pulse perturbations can have long-term legacies in soil microbial ecosystems. In our experiment they led to alternative system states which differed from the unperturbed control in multiple parameters even after 160 days. This indicates that soil microbial communities exhibit a low resistance and resilience towards single-pulse perturbations, and may easily be pushed on alternative trajectories by short but strong environmental pulses.

Dominant plant species alter stoichiometric imbalances between soil microbes and their resources in an alpine grassland: Implications for soil microbial respiration

Soil microbes are subject to stoichiometric imbalances, which are the dissimilarities in elemental stoichiometry between microbial biomass and resources. Shifts in dominant plant species co-occur with unparallel changes in the stoichiometry of soil microbial biomass and resources, leading to stoichiometric imbalances. However, how soil microbes deal with stoichiometric imbalances induced by changes in dominant plant species, and what the implications are for soil carbon cycling, remain unknown. Here, we compared the stoichiometric imbalances of five plant patch types with the dominant plant community (Kobresia pygmaea) in a Tibetan alpine grassland to examine how soil microbes respond physiologically to stoichiometric imbalances, thereby affecting soil microbial respiration (SMR). We found that C:N and C:P imbalances varied between plant patches and differed significantly from those in the soil of K. pygmaea. We also found that the regulation of extracellular enzyme production, SMR, potential microbial carbon use efficiency (CUE), net N mineralization, and net ammonification were essential mechanisms for soil microbes to deal with C:N imbalances. Simultaneously, soil microbes dealt with fluctuating C:P imbalances by regulating their net P mineralization and CUE. Further, structural equation modeling revealed that stoichiometric imbalances induced by changes in dominant plant species could indirectly affect SMR by regulating extracellular enzyme stoichiometry and net nutrient mineralization. These results highlight the importance of the stoichiometry of soil microbe/resource interactions in regulating metabolic activities and modifying terrestrial carbon flows in shifting plant communities.

Effects of multispecies restoration on soil extracellular enzyme activity stoichiometry in Pinus massoniana plantations of subtropical China

Multispecies restoration is considered a feasible practice to tackle the decline in ecosystem services provided by monocultures. However, our understanding of how multispecies restoration influences microbial catabolic and anabolic pathways in coniferous monocultures based on enzymatic stoichiometry remains limited. Here, to assess the microbial resource limitation and carbon (C) use efficiencies in topsoil and subsoil after multispecies restoration, we compared the soil enzyme activities and stoichiometry of two multispecies plantations (broadleaf-oriented transformation and replenishment with local broadleaved trees), two stand ages of Pinus massoniana monocultures, and secondary forests in subtropical China. According to the specific enzyme activities, the labile C decomposition was suppressed but the recalcitrant C decomposition was stimulated in the subsoil in multispecies restorations. Additionally, the vector analysis and microbial acquisition ratios consistently indicated that multispecies plantations aggravated the co-limitation of C and phosphorus (P) in the subsoil and that the limitation was equal to the level of secondary forests. We also found significant decreases in C use efficiencies in multispecies plantations compared with pine monocultures. These findings suggested a trade-off between obtaining multiple nutrients and increasing C use efficiency in the subsoil of forests with different restoration approaches. Furthermore, the microbial acquisition ratios and C use efficiencies were mainly influenced by soil pH and microbial biomass stoichiometry. Overall, our study integrated the microbial resource limitation and C use efficiency to provide an enzymatic perspective for underground C-cycling and nutrient mineralization after forest restoration, highlighting the critical role of multispecies plantations in inducing strong shifts in microbial metabolism, especially in the subsoil.

Effects of warming on the stoichiometry of soil microbial biomass and extracellular enzymes in an alpine shrubland

The alpine shrublands on the Qinghai-Tibetan Plateau are experiencing significant warming. Revealing the effects of warming on the soil microbial metabolism will provide insights into the dynamics of soil carbon (C) and nutrient cycling in these alpine ecosystems. A five-year warming experiment (+1.3 °C, using open-top chambers) was conducted in a Sibiraea angustata-dominated alpine shrubland on the eastern Qinghai-Tibetan Plateau. We examined the effects of warming on the stoichiometry of topsoil (0–15 cm) microbial biomass, extracellular enzyme activity and their relationships with soil physicochemical properties. The results showed that the effects of warming on the soil microbial biomass C, nitrogen (N) and phosphorus (P) varied with the growing season. Warming increased the activity levels of C-acquiring enzymes (β-glucosidase, BG) by 7.5 %-15.1 % throughout the growing season (P < 0.01) and the activity of polyphenol oxidase (PPO) by 6.5 % during the early growing season (P < 0.05), indicating that warming would strengthen microbial C limitation and increase degradation of soil labile and recalcitrant C components. Warming increased the activity of P-acquiring enzyme (acid phosphatase, AP) by 14.6 % (P < 0.01) and triggered microbial P limitation during the late growing season, which might be a result of an increasing alpine shrub P uptake. Warming did not affect the total activity levels of N-acquiring enzymes throughout the growing season (P > 0.05), mainly due to higher soil N availability. Warming did not affect the stoichiometry of soil extracellular enzymes throughout the growing season (P > 0.05), except for a decreasing in the enzyme N:P ratio during the early growing season (P < 0.05). Moreover, the microclimate (air and soil temperature), available soil nutrients (soil dissolved organic C and available P) and soil pH accounted for most of the variation in soil microbial biomass, extracellular enzyme activity and their stoichiometry in response to warming. Our results suggest that warming may trigger and strengthen soil microbial C and P limitation during the growing season, accelerating soil C loss and nutrient cycling in alpine shrublands on the Qinghai-Tibetan Plateau.

New insights into the patterns of ecoenzymatic stoichiometry in soil and sediment

Ecoenzymatic stoichiometry connects the elemental stoichiometry of microbial biomass and detrital organic matter to microbial nutrient assimilation and growth, and thus has been proposed and developed to estimate microbial nutrient limitations. However, the theories and methods developed so far have not yet clearly explored the critical thresholds of ecoenzymatic stoichiometry that identify whether nutrient limitation occurs or not. Here, we developed methods quantifying critical thresholds for microbial carbon (C), nitrogen (N) and phosphorus (P) limitations by centering on the potential responses of microbial resource use efficiency to nutrient limitations. We also provided new insight into the relationships of bivariate regressions between C-, N- and P-acquiring ecoenzymatic activities by reconsidering the intercept of regressions as an index to initial nutrient limitations, and consequently distinguished six initial limitation scenarios based on the range of values for these intercepts. According to the empirical values of the regression intercepts, the overall frequency of primary nutrient limitations in microbial communities across a global suite of soils and sediments is P limitation > N limitation > C limitation. The result implies that P and N availabilities rather than that of C could be the most important limitations on microbial production and metabolism in terrestrial soils and freshwater sediments. Nutrient limitations in heterotrophic microbial communities are fundamental characteristics of both soil and sediment systems, which regulate organic matter decomposition and element cycles. Our perspective provides a foundational framework and avenue for understanding and quantifying microbial nutrient limitations in studies of terrestrial C cycling and microbial ecology.

Decay processes in Salix psammophila sand barriers increase soil microbial element stoichiomery ratios

Salix psammophila sand barriers are a widely used engineering measure to control quicksand in northwest China. Thus, it is important to elucidate the influence of the sand barrier decay process on soil microbial ecological stoichiometric characteristics in desert environments. In the present study, field in situ sampling and laboratory index measurements were used to evaluate and compare the performance degradation, variation in soil physical and chemical properties, and soil microbial ecological stoichiometry of sand barriers during decay. The results showed that with the worsening of the decay degree, all indexes of the decay characteristics decreased significantly, among which the flexural strength of mechanical properties decreased the most, which directly led to collapse and damage. The cellulose and lignin contents of the chemical components also exhibited varying degrees of decomposition, and the soil physical and chemical properties showed a significant increase. The changes in the microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents were consistent with the trend of the soil properties, and both reached their peak at 7 years. With the aggravation of decay, the stoichiometric ratios of soil microbial elements C, N, and P increased continuously. However, there was no significant increase in MBC/MBP and MBN/MBP in the early period (≤3 years) of the sand barrier establishment, but there was a significant increase in the later period (≥5 years). These results indicated that S. psammophila sand barriers mainly played the role of windbreak and sand fixation in the early period, and made soil microorganisms susceptible to phosphorus limitation in the later period. Stepwise linear regression analysis showed that MBC/MBN, MBC/MBP, and MBN/MBP were mainly affected by basic density (BD). Therefore, the sand barrier changes soil properties by degrading its own chemical components during the decay process and the loss of basic density is the main driving factor for increasing the C:N:P stoichiometry of soil microbial biomass. It can still be further promoted and used in the resource utilization process of mechanical sand barriers in the future.

Eco-enzymatic stoichiometry and microbial non-homeostatic regulation depend on relative resource availability during litter decomposition

The relationships between soil eco-enzymatic stoichiometry and substrate stoichiometry could be used to explain nutrient cycling processes regulated by microbial biomass stoichiometry. But what are the relationships between the stoichiometry of resources, microorganisms, and enzymes? We do not have a clear understanding yet, particularly in the different stages of litter decomposition. By analyzing the response of extracellular enzymatic stoichiometry to the imbalance between microbial and substrate stoichiometry, we explore the microbial-mediated litter transformation and microbial adaptation mechanisms in the transformation interface soil (TIS) layer. The results showed that soil microbial metabolism was limited by C and P during decomposition, peaking in the transition (middle) stage and then gradually decreasing. According to the judgment of microbial homeostasis (effect of substrate stoichiometry on microbial biomass stoichiometry), the microbial communities shift from homeostatic in the early stage to non-homeostatic in the middle stage and then return to homeostasis in the later stage. During the litter decomposition, the non-homeostatic period corresponded to the transition stage. That means severe microbial metabolic limitation is a potential determinant of microbial homeostasis. Soil microorganisms adapt and alleviate microbial metabolic limitations by adjusting extracellular enzyme activity and microbial non-homeostatic behavior when the available resources fail to satisfy microbial requirements.

Plant community productivity is associated with multiple ecological stoichiometry in restoration grasslands

Ecological stoichiometry links the growth of living organisms at the organ level through the strict elemental ratio (carbon [C], nitrogen [N] as well as phosphorus [P]). And this is conducive to maintaining plant productivity in terrestrial ecosystems. Yet, the identification about the significance of multiple ecological stoichiometry (including leaves, roots, soil and microbial biomass) in shaping plant productivity remains unknown. Here, we evaluated the ecological stoichiometry contributions to plant productivity in restoration grasslands on the Loess Plateau (1-, 5-, 10-, 15-, 25-, 30-years restoration grasslands). We found that grassland restoration for 30 years enhanced plant community productivity by 67.34%, which showed the synchronous increase trend with C and N contents in leaves, roots, soil as well as microbial biomass. However, leaves, roots, soil and microbial biomass P contents displayed the opposite change trend with no significant difference in these restoration grasslands (p > 0.05). Microbial biomass C/N/P ratios exhibited thesignificant correlations with leaves, roots, soil C/N/P ratios, as well as plant community productivity (p < 0.01), indicating that stoichiometry of soil microbial biomass is greatly restricted, with the potential to influence plant community productivity. These findings emphasized the crucial role of microbial biomass stoichiometry as a primary regulator on plant community productivity, providing the important data to improve the parameterization of plant growth models in natural grassland of China.

Vegetation Restoration with Mixed N2-Fixer Tree Species Alleviates Microbial C and N Limitation in Surface Soil Aggregates in South Subtropical Karst Area, China

Soil extracellular enzyme stoichiometry (EES) is the essential predictor in nutrient status and resource limitation of soil microorganisms, whose metabolism has a vital role in biogeochemical cycling and ecosystem function. However, little is known about how N2-fixer tree species with different planting patterns affect soil nutrient resources in terms of extracellular enzyme activity (EEA) or EES within aggregates in degraded karst ecosystems. In this study, we evaluated soil EEA and EES related to carbon (C), nitrogen (N), and phosphorus (P) cycles across two eight-year-old pure plantations of legume species [Dalbergia odorifera T. Chen (PD) and Acrocarpus fraxinifolius Wight ex Arn. (PA)] and a mixed plantation of the two tree species listed above (MP). Meanwhile, a nearby undisturbed shrubland was used as a control (CK). We concluded that the activities of C-, N-, and P-acquiring enzyme increased to different degrees in the N2-fixer tree species stands (particularly in MP) compared to CK in all aggregates. Compared to CK, MP significantly increased by 39.0%, 54.0%, 39.3%, and 24.8% in total C-acquiring EEA, 41.1%, 60.5%, 47.8%, and 12.5% in total N-acquiring EEA, and 100.4%, 79.7%, 69.2%, and 56.4% in total P-acquiring EEA within &gt;2 mm, 1–2 mm, 0.25–1 mm, and &lt;0.25 mm aggregates, respectively. Furthermore, the logarithmic transformed ratio of C-, N-, and P-acquiring enzyme activities was 1.20:1.08:1, which deviated from the global ratio (1:1:1). Vector analysis of EEA showed that the vector length (VL) within aggregates was significantly lower than that of CK in all stands of N2-fixer species except PD; while in all treatments, vector angle (VA) was &lt;45° for all aggregate sizes, except in MP, where VA reached 45° for &lt;0.25 mm aggregate. These indicated soil microbes were limited by C and N together. However, MP significantly alleviated microbial C and N limitation than CK (p &lt; 0.05). There were obvious positive relationships between enzyme C:N, C:P, and N:P ratios. VL was markedly negatively linked to VA. EES was markedly related to most soil nutrients and microbial biomass stoichiometry ratios. Changes in soil EEA and EES were primarily driven by available phosphorus (AP), microbial biomass carbon (MBC), soil C:N and MBN:MBP ratios. Together, our results demonstrate the influences after introducing N2-fixer tree species (particularly MP) for vegetation recovery on soil microbial nutrient limitation and ecological processes in aggregate level and will contribute to the development of ecological restoration practices and fertility management in degraded karst ecosystems of southwest China.

Can multi-cropping affect soil microbial stoichiometry and functional diversity, decreasing potential soil-borne pathogens? A study on European organic vegetable cropping systems.

Crop diversification in spatial and temporal patterns can optimize the synchronization of nutrients plant demand and availability in soils, as plant diversity and soil microbial communities are the main drivers of biogeochemical C and nutrient cycling. The introduction of multi-cropping in organic vegetable production can represent a key strategy to ensure efficient complementation mediated by soil microbiota, including beneficial mycorrhizal fungi. This study shows the effect of the introduction of multi-cropping in five European organic vegetable systems (South-West: Italy; North-West: Denmark and Belgium; North-East: Finland and Latvia) on: (i) soil physicochemical parameters; (ii) soil microbial biomass stoichiometry; (iii) crop root mycorrhization; (iv) bacterial and fungal diversity and composition in crop rhizosphere; (v) relative abundance of selected fungal pathogens species. In each site, three cropping systems were considered: (1) crop 1—monocropping; (2) crop 2—monocropping; (3) crop 1—crop 2—intercropping or strip cropping. Results showed that, just before harvest, multi-cropping can increase soil microbial biomass amount and shape microbial community toward a predominance of some bacteria or fungi phyla, in the function of soil nutrient availability. We mainly observed a selection effect of crop type on rhizosphere microbiota. Particularly, Bacteroidetes and Mortierellomycota relative abundances in rhizosphere soil resulted in suitable ecological indicators of the positive effect of plant diversity in field, the first ones attesting an improved C and P cycles in soil and the second ones a reduced soil pathogens' pressure. Plant diversity also increased the root mycorrhizal colonization between the intercropped crops that, when properly selected, can also reduce the relative abundance of potential soil-borne pathogens, with a positive effect on crop productivity in long term.