Carbon Use Efficiency Research Articles

Biotic and abiotic factors affecting soil microbial carbon use efficiency

Soil microbial carbon use efficiency (CUE) refers to the efficiency of microorganisms in converting absorbed carbon into their own biomass carbon. Soil microbial CUE is a key parameter to understanding the soil carbon cycle. Biotic and abiotic factors are widely considered to be important factors influencing CUE. However, the related underlying mechanisms remain unclear. This review elaborates on the concept of soil microbial CUE and the various approaches used for its measurement. We reviewed the effects of various abiotic factors, such as temperature, soil moisture, pH, nutrient addition, and substrate type, and biotic factors, such as microbial community structure and diversity, on CUE. Finally, we discussed the focus areas that future studies need to further explore. We hope this review can provide a comprehensive understanding of the factors impacting soil microbial CUE, which is a fundamental step to improving soil carbon storage capacity.

Plant organic nitrogen nutrition: costs, benefits, and carbon use efficiency.

Differences in soil mobility and assimilation costs between organic and inorganic nitrogen (N) compounds would hypothetically induce plant phenotypic plasticity to optimize acquisition of, and performance on, the different N forms. Here we evaluated this hypothesis experimentally and theoretically. We grew Arabidopsis in split-root setups combined with stable isotope labelling to study uptake and distribution of carbon (C) and N from l-glutamine (l-gln) and NO3 - and assessed the effect of the N source on biomass partitioning and carbon use efficiency (CUE). Analyses of stable isotopes showed that 40-48% of C acquired from l-gln resided in plants, contributing 7-8% to total C of both shoots and roots. Plants grown on l-gln exhibited increased root mass fraction and root hair length and a significantly lower N uptake rate per unit root biomass but displayed significantly enhanced CUE. Our data suggests that organic N nutrition is linked to a particular phenotype with extensive growth of roots and root hairs that optimizes for uptake of less mobile N forms. Increased CUE and lower N uptake per unit root growth may be key facets linked to the organic N phenotype.

Simulated nitrogen deposition and precipitation events alter microbial carbon cycling during early stages of litter decomposition

Abstract Plant litter decomposition is a major nutrient input to terrestrial ecosystems that is primarily driven by microorganisms. Litter quality is considered a key drive of decomposition; however, human-induced global disturbance like nitrogen deposition and increasing extreme precipitation events will shift nutrient availability during litter decomposition. Little is known about how shifting nutrient availability will impact dissolved organic matter concentrations and microbially driven carbon cycling that are critical to soil organic matter formation. This study investigated the effect of simulated nitrogen deposition and repeated precipitation events on microbially-driven carbon flow during short-term litter decomposition using a ‘common garden’ experiment with microcosms containing sand and blue grama grass litter inoculated with different microbial communities. Overall, nitrogen deposition decoupled respiration and dissolved organic carbon (DOC) by increasing respiration and not affecting DOC concentrations. Moreover, nitrogen deposition had no effect on microbial carbon use efficiency (CUE). Repeated simulated precipitation events significantly increased DOC concentrations, decreased microbial CUE, increased the microbial metabolic quotient (qCO2), and altered microbial composition and diversity. These findings highlight the complex interactions and responses of surface litter decomposers to shifting nutrient availability and contradicts previous findings that nitrogen deposition will increase soil carbon sequestration from a larger supply of DOC and reduced respiration.

Factors influencing carbon and water use efficiency in changing environments

IntroductionVegetation plays a crucial role in terrestrial ecosystems, acting as a vital link connecting the lithosphere, hydrosphere, and atmosphere in terms of energy flow and material cycling. Changes in surface vegetation significantly regulate the water cycle, energy flow within terrestrial surfaces, and global carbon balance.MethodsThis study focuses on nine major river basins in China to quantitatively investigate the impacts of climate factors, vegetation dynamics, and land use changes on carbon use efficiency (CUE) and water use efficiency (WUE).ResultsThe primary controlling factors of WUE trends are NDVI (average contribution: 33.75% ± 6.90%) and VPD (average contribution: 28.04% ± 3.98%). NDVI predominates in the Haihe, Yellow River, Yangtze River, Pearl River, and Songliao River basins, while shortwave radiation (Srad) dominates in the southeastern rivers and inland river areas, and humidity (Shum) in the southwestern river basins. For CUE trends, the main controlling factors are Srad (average contribution: 36.46% ± 3.40%) and precipitation (Pre) (average contribution: 26.72% ± 5.20%). NDVI negatively influences the Huaihe River and southeastern river basins, while Pre negatively influences the Songliao River and Yellow River basins, and Srad negatively influences the Huaihe and southwestern river basins. Pre predominates in the Huaihe, Songliao, Haihe, southwestern river basins, and inland river areas, while Srad predominates in the Pearl River, Yangtze River, and Yellow River basins.DiscussionClimate factors and vegetation dynamics have significant regional impacts on WUE and CUE across different river basins, especially the roles of NDVI and VPD on WUE, and Srad and precipitation on CUE. These differences underscore the importance of developing region-specific management strategies to optimize ecosystem services in each basin.

Aridity-Driven Change in Microbial Carbon Use Efficiency and Its Linkage to Soil Carbon Storage.

Global warming is generally predicted to increase aridity in drylands, while the effects of aridity changes on microbial carbon use efficiency (CUE) and its linkage to soil organic carbon (SOC) storage remain unresolved, limiting the accuracy of soil carbon dynamic predictions under changing climates. Here, by employing large-scale soil sampling from 50 sites along an ~6000 km aridity gradient in northern China, we report a significant decreasing trend in microbial CUE (ranging from approximately 0.07 to 0.59 across the aridity gradient) with increasing aridity. The negative effect of aridity on microbial CUE was further verified by an independent moisture manipulation experiment, which revealed that CUE was lower under lower moisture levels than under higher moisture levels. Aridity-induced increases in physicochemical protection or decreases in microbial diversity primarily mediated the decrease in CUE with increasing aridity. Moreover, we found a highly positive microbial CUE-SOC relationship, and incorporating CUE improved the explanatory power of SOC variations along the aridity gradient. Our findings provide empirical evidence for aridity-induced reductions in microbial CUE over a broad geographic scale and highlight that increasing aridity may be a crucial mechanism underlying SOC loss by suppressing the ability of soil microorganisms to sequester carbon.

C/N conversion and pigment production of Blastochloris sulfoviridis characterized by bacteriochlorophyll b under near-infrared single-wavelength laser

High carbon use efficiency (CUE) of photosynthetic bacteria (PSB) can concurrently increase biomass and reduce CO2 emissions. In the PSB study, light-oxygen conditions are crucial factors influencing the growth of these bacteria. Bacteriochlorophyll (BChl) b (absorption spectra: 970–1040 nm), due to its unique absorption spectrum, can be considered a crucial complement to BChl a (absorption spectra: 780–890 nm). We investigate the effects of four light-oxygen conditions on biomass, C/N conversion, and pigment production using five individual light sources in Blastochloris sulfoviridis (B. sulfoviridis), producing BChl b, isolated using 940±10 nm laser unexpectedly. Biomass, CUE, and pigment production follow the order under different light-oxygen conditions: light-anaerobic > light-aerobic > dark-aerobic > dark-anaerobic. The maximum biomass (1386.88 mg/L), highest CUE (0.95 g-biomass/g-CODremoved and 0.49 g-biomass carbon/g-CODremoved), and highest pigment production are observed under full spectrum (40 W)-anaerobic, 940-anaerobic, and 850-anaerobic conditions, respectively. Compared to light-aerobic, the nitrogen-fixing ability of B. sulfoviridis is enhanced under light-anaerobic conditions. This study contributes to research on resource recovery and greenhouse gas emissions reduction in PSB wastewater treatment.

Soil viral–host interactions regulate microplastic-dependent carbon storage

Microplastic is globally regarded as an important factor impacting biogeochemical cycles, yet our understanding of such influences is limited by the uncertainties of intricate microbial processes. By multiomics analysis, coupled with soil chemodiversity characterization and microbial carbon use efficiency (CUE), we investigated how microbial responses to microplastics impacted soil carbon cycling in a long-term field experiment. We showed that biodegradable microplastics promoted soil organic carbon accrual by an average of 2.47%, while nondegradable microplastics inhibited it by 17.4%, as a consequence of the virus-bacteria coadaptations to the microplastics disturbance. In the relevant functional pathways, nondegradable microplastics significantly (P < 0.05) enhanced the abundance and transcriptional activity related to complex carbohydrate metabolism, whereas biodegradable microplastics significantly (P < 0.05) promoted functions involved in amino acid metabolism and glycolysis. Accordingly, viral lysis enhanced in nondegradable microplastics treatments to introduce more complex organic compounds to soil dissolved organic matters, thus benefiting the oligotrophs with high carbon metabolic capabilities in exploitation competition. In contrast, biodegradable microplastics enriched viral auxiliary metabolic genes of carbon metabolism through "piggyback-the-winner" strategy, conferring to dominant copiotrophs, enhanced substrate utilization capabilities. These virus-host interactions were also demonstrated in the corresponding soil plastisphere, which would alter microbial resource allocation and metabolism via CUE, affecting carbon storage consequently. Overall, our results underscore the importance of viral-host interactions in understanding the microplastics-dependent carbon storage in the soil ecosystem.

New insights into the prediction for the potential of soil organic carbon accumulation: From the perspective of non-equilibrium statistical mechanics

The accumulation of soil organic carbon (SOC) is significant for soil health and ecosystem services. Numerous studies have assessed the dynamic changes of SOC by considering the microbial system as an equilibrium system. However, they failed to reveal the complexity of the SOC accumulation/loss process, as the microbial system is a non-equilibrium system affected by stochastic fluctuations from the external environment. This study is the first to explore the complex non-equilibrium relationship between microbial carbon use efficiency (CUE) and SOC by using potential landscape and flux in non-equilibrium statistical mechanics. Nitrogen (N) was identified as the most critical environmental factor influencing CUE on a global scale, with the transition between the carbon loss state and the carbon sequestration state observed along N gradients. Random perturbations of other environmental factors could also trigger transition. Non-equilibrium thermodynamic quantities indicated that carbon sequestration had the potential to be achieved when N = 0.5 g/kg, where active soil management measures should be taken. Furthermore, the non-equilibrium relationship between CUE and SOC was clarified through potential energy analysis, where the average deviation between predictions and actual observations of SOC is about 1.9792 g/kg. This study provides an effective framework for predicting SOC accumulation.

Asymmetric winter warming reduces microbial carbon use efficiency and growth more than symmetric year-round warming in alpine soils

Asymmetric seasonal warming trends are evident across terrestrial ecosystems, with winter temperatures rising more than summer ones. Yet, the impact of such asymmetric seasonal warming on soil microbial carbon metabolism and growth remains poorly understood. Using 18O isotope labeling, we examined the effects of a decade-long experimental seasonal warming on microbial carbon use efficiency (CUE) and growth in alpine grassland ecosystems. Moreover, the quantitative stable isotope probing with 18O-H2O was employed to evaluate taxon-specific bacterial growth in these ecosystems. Results show that symmetric year-round warming decreased microbial growth rate by 31% and CUE by 22%. Asymmetric winter warming resulted in a further decrease in microbial growth rate of 27% and microbial CUE of 59% compared to symmetric year-round warming. Long-term warming increased microbial carbon limitations, especially under asymmetric winter warming. Long-term warming suppressed the growth rates of most bacterial genera, with asymmetric winter warming having a stronger inhibition on the growth rates of specific genera (e.g., Gp10, Actinomarinicola, Bosea, Acidibacter, and Gemmata) compared to symmetric year-round warming. Bacterial growth was phylogenetically conserved, but this conservation diminished under warming conditions, primarily due to shifts in bacterial physiological states rather than the number of bacterial species and community composition. Overall, long-term warming escalated microbial carbon limitations, decreased microbial growth and CUE, with asymmetric winter warming having a more pronounced effect. Understanding these impacts is crucial for predicting soil carbon cycling as global warming progresses.

Enhanced carbon use efficiency and warming resistance of soil microorganisms under organic amendment

The frequency and intensity of extreme weather events, including rapid temperature fluctuations, are increasing because of climate change. Long-term fertilization practices have been observed to alter microbial physiology and community structure, thereby affecting soil carbon sequestration. However, the effects of warming on the carbon sequestration potential of soil microbes adapted to long-term fertilization remain poorly understood. In this study, we utilized 18O isotope labeling to assess microbial carbon use efficiency (CUE) and employed stable isotope probing (SIP) with 18O-H2O to identify growing taxa in response to temperature changes (5–35 °C). Organic amendment with manure or straw residue significantly increased microbial CUE by 86–181 % compared to unfertilized soils. The microorganisms inhabiting organic amended soils displayed greater resistance of microbial CUE to high temperatures (25–35 °C) compared to those inhabiting soils fertilized only with minerals. Microbial growth patterns determined by the classification of taxa into incorporators or non-incorporators based on 18O incorporation into DNA exhibited limited phylogenetic conservation in response to temperature changes. Microbial clusters were identified by grouping taxa with similar growth patterns across different temperatures. Organic amendments enriched microbial clusters associated with increased CUE, whereas clusters in unfertilized or mineral-only fertilized soils were linked to decreased CUE. Specifically, shifts in the composition of growing bacteria were correlated with enhanced microbial CUE, whereas modifications in the composition of growing fungi were associated with diminished CUE. Notably, the responses of microbial CUE to temperature fluctuations were primarily driven by changes in the bacterial composition. Overall, our findings demonstrate that organic amendments enhance soil microbial CUE and promote the enrichment of specific microbial clusters that are better equipped to cope with temperature changes. This study establishes a theoretical foundation for manipulating soil microbes to enhance carbon sequestration under global climate scenarios.

Evaluating variation of respiration:photosynthesis ratio in sagebrush species: Implications for carbon flux modeling

AbstractPlant respiration and photosynthesis are the two main processes influencing carbon (C) flux balance at leaf‐to‐ecosystem scales. The ratio of respiration to photosynthesis (R:A) or carbon use efficiency (CUE) is considered an important trait for determining global carbon storage in the near future. One school of thought assumes that R:A is constant in terrestrial productivity models, irrespective of biomass, climate, and species. Others believe it is variable, although within a limited range. Semiarid systems dominated by woody vegetation, such as sagebrush steppe, have been recognized as potentially important C sinks on regional to global scales in the context of future climate scenarios. Therefore, there is a critical need to study R:A over different organizational scales (i.e., at the leaf, whole plant, and ecosystem scales) to use this approach for future C flux predictions under climate change scenarios. The objective of this study was to compare leaf‐, shrub‐, and ecosystem‐scale R:A among three sagebrush (Artemisia spp.) communities, and to determine how R:A varies throughout the growing season (i.e., early, mid‐, and late summer) among these communities. We measured photosynthesis and respiration monthly in three sagebrush communities spanning a 685‐m elevation gradient at the Reynolds Creek Experimental Watershed and Critical Zone Observatory in southwestern Idaho. Consistent with our expectations, we found large seasonal variations in R and A at all scales, but with differences in A among the three sagebrush communities significant only at the leaf scale. The R:A ratio was not significantly different among the three species at all organizational scales. However, the R:A ratio did vary among months at the leaf level and there was a statistical interaction between species and month at both leaf and shrub levels. Our study indicates that the R:A ratio is generally conservative, although not tightly constrained (range: 0.12–0.77) among three sagebrush species. Therefore, approaches that assume conservative R:A ratios in terrestrial productivity models need to be considered carefully to evaluate the impact of projected climatic changes on future C cycling in shrub‐dominated rangeland ecosystems.

Control of inorganic and organic phosphorus molecules on microbial activity, and the stoichiometry of nutrient cycling in soils in an arid, agricultural ecosystem

Background The dynamics of carbon (C), nitrogen (N), and phosphorus (P) in soils determine their fertility and crop growth in agroecosystems. These dynamics depend on microbial metabolism, which in turn depends on nutrient availability. Farmers typically apply either mineral or organic fertilizers to increase the availability of nutrients in soils. Phosphorus, which usually limits plant growth, is one of the most applied nutrients. Our knowledge is limited regarding how different forms of P impact the ability of microbes in soils to produce the enzymes required to release nutrients, such as C, N and P from different substrates. Methods In this study, we used the arable layer of a calcareous soil obtained from an alfalfa cropland in Cuatro Cienegas, México, to perform an incubation experiment, where five different phosphate molecules were added as treatments substrates: three organic molecules (RNA, adenine monophosphate (AMP) and phytate) and two inorganic molecules (calcium phosphate and ammonium phosphate). Controls did not receive added phosphorus. We measured nutrient dynamics and soil microbial activity after 19 days of incubation. Results Different P molecules affected potential microbial C mineralization (CO2-C) and enzyme activities, specifically in the organic treatments. P remained immobilized in the microbial biomass (Pmic) regardless of the source of P, suggesting that soil microorganisms were limited by phosphorus. Higher mineralization rates in soil amended with organic P compounds depleted dissolved organic carbon and increased nitrification. The C:N:P stoichiometry of the microbial biomass implied a change in the microbial community which affected the carbon use efficiency (CUE), threshold elemental ratio (TER), and homeostasis. Conclusion Different organic and inorganic sources of P affect soil microbial community structure and metabolism. This modifies the dynamics of soil C, N and P. These results highlight the importance of considering the composition of organic matter and phosphate compounds used in agriculture since their impact on the microbial activity of the soil can also affect plant productivity.

Effects of MCPA and difenoconazole on glyphosate degradation and soil microorganisms

Modern agriculture relies heavily on pesticide use to meet the demands of food quality and quantity. Therefore, pesticides are often applied in mixtures, leading to a diverse cocktail of chemicals and their metabolites in soils, which can affect non-target organisms such as soil microorganisms. Pesticides are tested for their single effects, but studies on their interactive effects are scarce. This study aimed to determine the effects of up to three simultaneously applied pesticides on the soil microbial community and on their special function in pesticide degradation. Agricultural soil without previous pesticide application was exposed to different mixtures of the herbicide glyphosate (GLP), the phenoxy herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) and the fungicide difenoconazole (DFC) for up to 56 days. Isotopic and molecular methods were used to investigate effects of the mixtures on the microbial community and to follow the mineralization and utilization of GLP. An initial increase in the metabolic quotient by up to 35 % in the presence of MCPA indicated a stress reaction of the microbial community. The presence of multiple pesticides reduced both gram positive bacterial fatty acid methyl esters (FAMEs) by 13 % and the abundance of microorganisms with the genetic potential for GLP degradation via the AMPA (aminomethylphosphonic acid) pathway. Both the number of pesticides and the identities of individual pesticides played major roles. Surprisingly, an increase in 13C-labelled GLP mineralization of up to 40 % was observed while carbon use efficiency (CUE) decreased. Interactions between multiple pesticides might alter the behavior of individual pesticides and be reflected in the microbial community. Our results highlight the importance of investigating not only single pesticides, but also pesticide mixtures and their interactions.

Temperature controls the relation between soil organic carbon and microbial carbon use efficiency.

Microbial carbon use efficiency (CUE) is an important variable mediating microbial effects on soil organic carbon (SOC) since it summarizes how much carbon is used for microbial growth or is respired. Yet, the role of CUE in regulating SOC storage remains debated, with evidence for both positive and negative SOC-CUE relations. Here, we use a combination of measured data around the world and numerical simulations to explore SOC-CUE relations accounting for temperature (T) effects on CUE. Results reveal that the sign of the CUE-T relation controls the direction of the SOC-CUE relations. A negative CUE-T relation leads to a positive SOC-CUE relation and vice versa, highlighting that CUE-T patterns significantly affect how organic carbon is used by microbes and hence SOC-CUE relations. Numerical results also confirm the observed negative SOC-T relation, regardless of the CUE-T patterns, implying that temperature plays a more dominant role than CUE in controlling SOC storage. The SOC-CUE relation is usually negative when temperature effects are isolated, even though it can become positive when nonlinear microbial turnover is considered. These results indicate a dominant role of CUE-T patterns in controlling the SOC-CUE relation. Our findings help to better understand SOC and microbial responses to a warming climate.

Does vegetation greening have a positive effect on global vegetation carbon and water use efficiency?

Terrestrial ecosystems have undergone significant changes as a result of climate change, profoundly affecting global carbon and water cycling processes. Notably, the synergistic changes in vegetation carbon use efficiency (CUE) and water use efficiency (WUE) and their response to patterns of climate change over the last 40 years are unknown. Therefore, in this study, global vegetation WUE and CUE were inverted using Gross primary productivity (GPP), Net primary productivity (NPP) and total evaporation (ET) data from 1981 to 2019 to reveal their temporal and spatial patterns of change through trend analysis and stability analysis. A stepwise regression algorithm was used to reveal the potential driving law of environmental factors on vegetation WUE and CUE. The results shows that (1) From 1981 to 2019, the global vegetation WUE and CUE showed in a relatively stable state, and the trends of WUE and CUE were -0.00004/year and 0.006 g C m−2 mm−1/year, respectively; (2) the greening of vegetation was the most important cause of the changes in WUE and CUE, and the driving force of rain and heat conditions on the CUE of vegetation was smaller than that of solar radiation and soil water, the regions where CO2 is the dominant factor affecting CUE and WUE are mainly in the north temperate zone; (3) the region of synergistic growth of WUE and CUE accounts for about 31.38 % of the global terrestrial area, and this pattern of change suggests that the global vegetation carbon sink potential is huge, and the popularization of vegetation planting patterns under the synergistic growth of CUE and WUE should be strengthened. The research has shown that vegetation greening is a key factor influencing changes in the WUE and CUE of vegetation, therefore, the implementation of ecological engineering will be an important step in combating climate change.

Changes in microbial physiology and carbon-use efficiency upon improving soil habitat conditions in conservation farming systems

The interplay between soil microbial anabolism and metabolism has recently been postulated as an important lever for carbon sequestration in soils. Theoretical considerations suggest that high microbial growth rates and a high carbon-use efficiency (CUE) are associated with increased soil organic carbon (SOC) build-up in arable soils. Nature-oriented conservation agricultural practices are believed to facilitate this microbial-driven process of SOC accrual; a practical validation of this postulation is however missing. Against this background, we evaluated the effect of agricultural management and site-specific soil chemical and physical properties on microbial physiology (i.e., respiration, bacterial and fungal growth rates, and microbial biomass turnover) and CUE by an on-farm comparison of conventional farming, conservation farming and unmanaged reference soil systems (i.e., adjacent field margins) at twenty-one sites across three soil depths. We show that a change in agricultural management towards soil health regeneration has a significant impact on microbial physiology. Bacterial growth, respiration and microbial biomass turnover increased from conventional farming towards conservation farming systems to reference soils. The opposite trend however was found for fungal growth and microbial CUE, with highest values observed in conventional farming systems. This clearly contradicts the prevailing idea that higher microbial CUE in conservation farming systems may be associated with higher SOC contents. Our results further show that soil physical and chemical parameters such as soil pH, texture and dissolved carbon compounds strongly predict microbial CUE. In line with these results, functional pore domains showed specific optima for microbial growth and CUE. For example, a high share of small pore domains hampered fungal growth and reduced microbial CUE but facilitated microbial biomass turnover at the same time. Thus, we suggest that – superimposed upon agricultural management effects – habitat structural conditions and microbial carbon limitation mainly shape microbial physiology and CUE in arable soil systems.

Mixed Eucalyptus plantations enhance soil organic carbon accumulation and chemical stability through soil microbial community and multifunctionality

Forest conversion can impact soil organic carbon (SOC) fixation and ecosystem functions. The newly proposed “evenness of SOC chemical components” index can indicate the permanence of stored SOC during environmental disturbances. However, how the mixing of tree species impacts SOC accumulation and persistence and changes in soil microbial communities and multifunctionality remain unknown. Thus, we conducted a field experiment (11 years) of monospecific Eucalyptus urophylla × E. grandis plantation for evaluating the influences of the mixed planting of a non-nitrogen (N)-fixing tree, Castanopsis hystrix, and an N-fixing tree, Dalbergia odorifera, on SOC accumulation and chemical stability. Compared with pure plantations, mixed Eucalyptus plantations (particularly those mixed with D. odorifera) exhibited significantly increased SOC concentrations by 28.60–33.71 % and increased SOC chemical component evenness by 3.96–4.67 % (P < 0.05). We also found that the concentrations and chemical component evenness of SOC were strongly linked with litter quality, soil N, phosphorus and their availability, multifunctionality, microbial activity, carbon use efficiency (CUE), biomass, diversity, and network complexity. Furthermore, tree species mixing increased litter quality, soil nutrient availability, microbial biomass, activity, diversity, CUE, and network complexity. Soil microbial anabolism, community characteristics and multifunctionality influenced the SOC concentrations and SOC chemical components evenness. Specifically, microbial diversity enhanced the concentrations and chemical component evenness of SOC by increasing network complexity and soil multifunctionality. These findings revealed differential responses and mechanistic controls of SOC accumulation and chemical stability in different Eucalyptus planting patterns. Overall, mixed plantations, particularly those in which N-fixing species were introduced, effectively improved SOC accumulation and stabilization by positively altering soil quality and microbial properties, potentially representing a sustainable forestry management strategy to improve soil C benefits and multifunctionality in forest ecosystems.

The response of terrestrial vegetation carbon use efficiency to global environmental changes

Terrestrial vegetation carbon use efficiency (CUE) is a key measure for assessing carbon transfer from the atmosphere to terrestrial biomass, crucial for understanding carbon cycling and allocation in ecosystems. CUE provides valuable insights into how terrestrial ecosystems respond to environmental changes. In this study, we utilized satellite datasets (MODIS and GLASS), MsTMIP models, and TRENDY models to analyze the spatiotemporal distribution characteristics of global vegetation CUE. We found that the average CUE for global land vegetation is 0.44 ± 0.06, with a slight annual increase and significant spatial heterogeneity, characterized by latitude gradients and vegetation types. High-latitude regions demonstrated higher CUE values compared to low-latitude regions. Further employing an integrated attribution approach, we identified the response mechanisms of vegetation CUE to global changes. The comprehensive response of vegetation CUE to climate change, land use change, atmospheric CO2, and nitrogen deposition was found to fluctuate and increase, with a model-averaged CUE increase of approximately 0.01. Land use change was identified as the largest contributor to the annual trend of overall global CUE (48.8%), while climate change was the main factor influencing the interannual variability (IAV) of global CUE (91.7%). Regarding global distribution, the IAV of vegetation CUE is mainly influenced by climate change. CUE annual trends in more regions were influenced by climate change, with 65% and 73% of the ensemble mean of the MsTMIP and TRENDY models, respectively. The results of the MsTMIP and TRENDY models consistently show that, globally, land use change affects about a quarter of the total annual trend of CUE. Land use change affected CUE annual trends to a greater extent than climate change. In addition, the vegetation type most affected by climate change is the deciduous needleleaf forests, and the CUE annual trend of cropland is most affected by land use change. Our findings reveal global patterns and drivers of CUE variability, highlighting the significant impact of climate change and land use change.

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.

Environment and microbiome drive different microbial traits and functions in the macroscale soil organic carbon cycle.

Soil microbial traits and functions play a central role in soil organic carbon (SOC) dynamics. However, at the macroscale (regional to global) it is still unresolved whether (i) specific environmental attributes (e.g., climate, geology, soil types) or (ii) microbial community composition drive key microbial traits and functions directly. To address this knowledge gap, we used 33 grassland topsoils (0-10 cm) from a geoclimatic gradient in Chile. First, we incubated the soils for 1 week in favorable standardized conditions and quantified a wide range of soil microbial traits and functions such as microbial biomass carbon (MBC), enzyme kinetics, microbial respiration, growth rates as well as carbon use efficiency (CUE). Second, we characterized climatic and physicochemical properties as well as bacterial and fungal community composition of the soils. We then applied regression analysis to investigate how strongly the measured microbial traits and functions were linked with the environmental setting versus microbial community composition. We show that environmental attributes (predominantly the amount of soil organic matter) determined patterns of MBC along the gradient, which in turn explained microbial respiration and growth rates. However, respiration and growth normalized for MBC (i.e., specific respiration and growth) were more linked to microbial community composition than environmental attributes. Notably, both specific respiration and growth followed distinct trends and were related to different parts of the microbial community, which in turn resulted in strong effects on microbial CUE. We conclude that even at the macroscale, CUE is the result of physiologically decoupled aspects of microbial metabolism, which in turn is partially determined by microbial community composition. The environmental setting and microbial community composition affect different microbial traits and functions, and therefore both factors need to be considered in the context of macroscale SOC dynamics.