Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation ...events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.
Future changes in precipitation will strongly impact ecosystem functioning and services through changes in plant growth. Here, we synthesize 83 precipitation experiments to look at responses of above and belowground plant growth (ANPP and BNPP) across climatic gradients and levels of precipitation change extremity. Overall, we found that (1) ANPP was more responsive to precipitation increases than decreases, and this was especially evident in dry ecosystems; (2) BNPP responses were similar under precipitation increases vs. decreases; (3) under extreme wet conditions, NPP responses leveled off, creating a saturating function of NPP response vs. the magnitude of precipitation change. Based on these findings, we suggest that future research focus on BNPP and plant responses to extreme precipitation change.
The insurance hypothesis, stating that biodiversity can increase ecosystem stability, has received wide research and political attention. Recent experiments suggest that climate change can impact how ...plant diversity influences ecosystem stability, but most evidence of the biodiversity–stability relationship obtained to date comes from local studies performed under a limited set of climatic conditions. Here, we investigate how climate mediates the relationships between plant (taxonomical and functional) diversity and ecosystem stability across the globe. To do so, we coupled 14 years of temporal remote sensing measurements of plant biomass with field surveys of diversity in 123 dryland ecosystems from all continents except Antarctica. Across a wide range of climatic and soil conditions, plant species pools, and locations, we were able to explain 73% of variation in ecosystem stability, measured as the ratio of the temporal mean biomass to the SD. The positive role of plant diversity on ecosystem stability was as important as that of climatic and soil factors. However, we also found a strong climate dependency of the biodiversity–ecosystem stability relationship across our global aridity gradient. Our findings suggest that the diversity of leaf traits may drive ecosystem stability at low aridity levels, whereas species richness may have a greater stabilizing role under the most arid conditions evaluated. Our study highlights that to minimize variations in the temporal delivery of ecosystem services related to plant biomass, functional and taxonomic plant diversity should be particularly promoted under low and high aridity conditions, respectively.
Climate and litter quality have been identified as major drivers of litter decomposition at large spatial scales. However, the role played by soil fauna remains largely unknown, despite its ...importance for litter fragmentation and microbial activity. We synthesised litterbag studies to quantify the effect sizes of soil fauna on litter decomposition rates at the global and biome scales, and to assess how climate, litter quality and soil fauna interact to determine such rates. Soil fauna consistently enhanced litter decomposition at both global and biome scales (average increment ~ 27%). However, climate and litter quality differently modulated the effects of soil fauna on decomposition rates between biomes, from climate‐driven biomes to those where climate effects were mediated by changes in litter quality. Our results advocate for the inclusion of biome‐specific soil fauna effects on litter decomposition as a mean to reduce the unexplained variation in large‐scale decomposition models.
Soils represent the largest carbon (C) pool in terrestrial ecosystems. The preservation and increase of soil C play a significant role in the fight against climate change, and can deliver other key ...ecosystem services beyond climate mitigation.
Soil C responses to climate change are largely driven by soil microbial communities, but they still represent a major source of uncertainty when predicting soil C variation in space and time.
This Special Feature identifies emerging findings from soil microbial ecology and climate change research that can reduce such uncertainty if incorporated into theory and models. The contributions span from novel perspectives on the priming effect and soil microbial enzymes, to understudied key biomes for global soil C such as tropical forests, to plant inputs–microbial necromass–mineral interactions, to soil C and microbial responses to changing precipitation patterns and recent advances in trait‐based and soil C modelling.
Together, this collection of papers draws attention to novel frameworks and ideas that can pave the road for future research on microbial contribution to soil C turnover and storage under climate change.
Resumen
Los suelos representan la mayor reserva de carbono (C) de los ecosistemas terrestres. La preservación y el aumento del C del suelo (CS) desempeñan un papel importante en la lucha contra el cambio climático y pueden ofrecer otros servicios ecosistémicos clave más allá de la mitigación del clima.
Las respuestas del CS frente al cambio climático son controladas en gran medida por las comunidades microbianas del suelo. A pesar de esta importancia, dichos organismo aún generan incertidumbre en los modelos que predicen la variación del CS en el espacio y el tiempo.
Este Número Especial identifica hallazgos recientes de la ecología microbiana del suelo y la ciencia del cambio climático que pueden reducir dicha incertidumbre si se incorporan a la teoría y a los modelos. Las contribuciones incluidas abarcan temas diversos. Desde nuevas perspectivas sobre el efecto ‘priming’ y las enzimas microbianas del suelo, hasta el estudio de los bosques tropicales como bioma clave, pero poco estudiado, para el C global. También se discuten las interacciones entre las plantas, la necromasa microbiana y los minerales, así como las respuestas del CS y los microorganismos a los cambios en las precipitaciones. Por último, se revisan avances recientes en el modelado del CS basado en rasgos funcionales.
En conjunto, esta colección de artículos identifica nuevos marcos e ideas que pueden favorecer futuras investigaciones sobre la contribución microbiana al almacenamiento y ciclado del CS bajo escenarios de cambio climático.
Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposition, and their activities (EEAs) play a key role in determining soil respiration (SR). Both EEAs and SR are highly ...sensitive to temperature, but their responses to climate warming remain poorly understood. Here, we present a meta‐analysis on the response of soil cellulase and ligninase activities and SR to warming, synthesizing data from 56 studies. We found that warming significantly enhanced ligninase activity by 21.4% but had no effect on cellulase activity. Increases in ligninase activity were positively correlated with changes in SR, while no such relationship was found for cellulase. The warming response of ligninase activity was more closely related to the responses of SR than a wide range of environmental and experimental methodological factors. Furthermore, warming effects on ligninase activity increased with experiment duration. These results suggest that soil microorganisms sustain long‐term increases in SR with warming by gradually increasing the degradation of the recalcitrant carbon pool.
The links between extracellular enzyme activities (EEAs) and soil respiration (SR) under warming scenarios remain poorly understood, despite both EEAs and SR are highly sensitive to temperatures. By synthesizing data from 56 studies, we showed that warming significantly increased ligninase activity by 21.4% and SR by 15.8%, while warming had no effect on cellulase activity. Moreover, increases in ligninase activity were positively correlated with SR and warming duration. These results reveal a novel mechanism that warming‐induced shifts in carbon‐degrading EEAs could contribute to the self‐reinforcing SR to long‐term climate warming.
Climate, litter quality and decomposers drive litter decomposition. However, little is known about whether their relative contribution changes at different decomposition stages. To fill this gap, we ...evaluated the relative importance of leaf litter polyphenols, decomposer communities and soil moisture for litter C and N loss at different stages throughout the decomposition process. Although both microbial and nematode communities regulated litter C and N loss in the early decomposition stages, soil moisture and legacy effects of initial differences in litter quality played a major role in the late stages of the process. Our results provide strong evidence for substantial shifts in how biotic and abiotic factors control litter C and N dynamics during decomposition. Taking into account such temporal dynamics will increase the predictive power of decomposition models that are currently limited by a single‐pool approach applying control variables uniformly to the entire decay process.
Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2O), but it remains ...unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N‐induced changes in soil N2O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2O emission by 261%, whereas there was no clear relationship between changes in soil N2O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field‐based results challenge the laboratory‐based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N‐induced changes in soil N2O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2O emission.
Our synthesis shows no clear relationship between changes in in‐situ soil N2O emission and shifts in ammonia oxidizer and denitrifier abundances under nitrogen loading. However, precipitation, soil pH, soil C:N ratio, and ecosystem type explain N‐induced changes in soil N2O emission at the global scale, suggesting the importance of key abiotic factors in modulating soil N2O emission. Caution is therefore required when extrapolating the laboratory‐based direct linkages between soil N2O emission and microbial guild abundances into Earth system models.
The degree to which climate warming will stimulate soil organic carbon (SOC) losses via heterotrophic respiration remains uncertain, in part because different or even opposite microbial physiology ...and temperature relationships have been proposed in SOC models. We incorporated competing microbial carbon use efficiency (CUE)–mean annual temperature (MAT) and enzyme kinetic–MAT relationships into SOC models, and compared the simulated mass‐specific soil heterotrophic respiration rates with multiple published datasets of measured respiration. The measured data included 110 dryland soils globally distributed and two continental to global‐scale cross‐biome datasets. Model–data comparisons suggested that a positive CUE–MAT relationship best predicts the measured mass‐specific soil heterotrophic respiration rates in soils distributed globally. These results are robust when considering models of increasing complexity and competing mechanisms driving soil heterotrophic respiration–MAT relationships (e.g., carbon substrate availability). Our findings suggest that a warmer climate selects for microbial communities with higher CUE, as opposed to the often hypothesized reductions in CUE by warming based on soil laboratory assays. Our results help to build the impetus for, and confidence in, including microbial mechanisms in soil biogeochemical models used to forecast changes in global soil carbon stocks in response to warming.
Model simulations incorporating a positive CUE–MAT relationship are consistent with the mass‐specific soil heterotrophic respiration rates patterns found in soils across the globe. That is, at a common assay temperature, both the measured and simulated mass‐specific soil heterotrophic respiration rates are lower for soils sampled from warmer climates. A negative CUE–MAT relationship, however, is unable to predict the observed patterns.
Summary
Plant leaf litter comprises the major common source of energy and nutrients in forested soil and freshwater ecosystems world‐wide. However, despite the similarity of physical and biochemical ...processes, generalizations across aquatic and terrestrial ecosystems regarding litter decomposition drivers remain elusive.
We re‐analysed data from a published field decomposition experiment conducted in two ecosystems (forest floors and streams) across five biomes (from the tropics to subarctic) with increasing decomposer community complexity (microbes, microbes and mesofauna, microbes and meso‐ and macrofauna).
Using a wide litter quality gradient (15 litter combinations), we aimed to disentangle the roles of decomposer community complexity from that of leaf litter traits (18 traits encompassing four broad trait categories: nutrients, C quality, physical structure and stoichiometry) on litter C and N loss. Comparisons of decomposition drivers between ecosystems were evaluated across and within biomes.
Differences in environmental conditions (e.g. climate, soil/water fertility) and litter nutrients – with a particular focus on Mg and Ca – across biomes were the major drivers of litter C loss in both ecosystems, but decomposer complexity also played a prominent role in streams. Within biomes, we observed consistent effects of litter nutrients and stoichiometry on litter C and N loss between ecosystems, but the effects of decomposer complexity differed between streams and forest floors in the temperate, Mediterranean and tropical biomes.
Our results highlight that, beyond the litter traits commonly identified as controlling decomposition (e.g. C, N and lignin), micronutrients (e.g. Mg and Ca) can also play an important, and globally consistent, role in both aquatic and terrestrial ecosystems. In addition, in forest streams the complexity of decomposer communities had similar importance as litter traits for predicting litter C and N turnover across all five biomes.
The identification of common drivers in our large‐scale ecosystem comparison suggests a basis to develop common models across aquatic and terrestrial ecosystems for C and N dynamics during decomposition. Future modelling efforts should account for the global similarities (litter micronutrient effects) and biome‐level differences (contingent decomposer effects) found between ecosystems.
Lay Summary
Soil carbon losses to the atmosphere through soil respiration are expected to rise with ongoing temperature increases, but available evidence from mesic biomes suggests that such response disappears ...after a few years of experimental warming. However, there is lack of empirical basis for these temporal dynamics in soil respiration responses, and for the mechanisms underlying them, in drylands, which collectively form the largest biome on Earth and store 32% of the global soil organic carbon pool. We coupled data from a 10 year warming experiment in a biocrust‐dominated dryland ecosystem with laboratory incubations to confront 0–2 years (short‐term hereafter) versus 8–10 years (longer‐term hereafter) soil respiration responses to warming. Our results showed that increased soil respiration rates with short‐term warming observed in areas with high biocrust cover returned to control levels in the longer‐term. Warming‐induced increases in soil temperature were the main drivers of the short‐term soil respiration responses, whereas longer‐term soil respiration responses to warming were primarily driven by thermal acclimation and warming‐induced reductions in biocrust cover. Our results highlight the importance of evaluating short‐ and longer‐term soil respiration responses to warming as a mean to reduce the uncertainty in predicting the soil carbon–climate feedback in drylands.
We investigated the temporal dynamics of soil respiration responses to temperature, and the mechanisms underlying them, in a biocrust‐dominated dryland ecosystem, coupling data from a 10 year field warming experiment with laboratory incubations. Our results showed that increased soil respiration rates with short‐term warming observed in areas with high biocrust cover returned to control levels in the longer‐term. Contrasting mechanisms underlie such responses. Specifically, warming‐induced increases in soil temperature were the main drivers of the short‐term soil respiration responses, whereas longer‐term soil respiration responses to warming were primarily driven by thermal acclimation and warming‐induced reductions in biocrust cover.
PDF
