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Climate change is projected to cause not only higher mean temperatures but also higher climate variability. Although elevated CO2 concentrations can potentially increase the productivity of some ecosystems, higher temperatures and more frequent droughts may lead to increased respiration and mortality, possibly negating these productivity gains. The capacity of global forests to adjust to climate change depends on their functional diversity and the ecosystem’s adaptive capacity.The Plant-FATE eco-evolutionary model describes vegetation responses to altered environmental conditions, including CO2 concentrations, temperatures, and droughts. It represents functional diversity by modelling species as points in trait space and incorporates ecosystem adaptations at three levels: 1) to model acclimation of plastic traits of individual plants, we leverage the power of eco-evolutionary optimality principles, 2) to model shifts in species composition via demographic changes and species immigration, we implement a trait-size-structured demographic vegetation model, and 3) to model the long-term genetic evolution of species, we have developed new evolutionary theory for trait-size-structured communities.First, we show that with just a few calibrated parameters, the Plant-FATE model accurately predicts the fluxes of CO2 and water, size distributions, and trait distributions for a tropical wet site in the Amazon Forest. Second, we show that under elevated CO2 conditions and in the absence of nutrient limitation, our model predictions are broadly consistent with observations, namely: an increase in leaf area, productivity and biomass, and a decrease in stomatal conductance and photosynthetic capacity. Third, we simulate the calibrated model with hypothetical future drought regimes to investigate three key features of ecosystem responses: 1) the change in species composition and ecosystem functioning in response to altered conditions, 2) the timescales of ecosystem response to new regimes, 3) the influence of functional diversity on the timescale of ecosystem adaptation and its consequences for ecosystem collapse.Our eco-evolutionary vegetation modelling strategy presents a powerful approach to leverage the power of natural selection to simulate ecosystem dynamics under novel conditions that plants may have never experienced before.

In early stages of forest succession plants have a high nutrient demand, but it is still a matter of debate if regrowth success of pioneer species is related to plant functional traits favoring fast soil colonization and nutrient acquisition. In general, we would expect trade-offs between plant growth performance and fine root morphological properties in association with different plant life-history strategies. Hence, we hypothesized that fast growing plants should have a more efficient root system that allows them to outcompete slow-growing neighbors in a resource-limited environment.To test our hypothesis we monitored plant successional growth dynamics in a tropical lowland rainforest reforestation experiment conducted in southwest Costa Rica. We collected absorptive roots (

Large amounts of carbon flow through tropical ecosystems every year, from which a part is sequestered in biomass through tree growth. However, the effects of ongoing warming and drying on tree growth and carbon sequestration in tropical forest is still highly uncertain. Field observations are sparse and limited to a few sites, while remote sensing analysis shows diverging growth responses to past droughts that cannot be interpreted with confidence. To reconcile data from field observations and remote sensing, we collated in situ measurements of stem growth and leaf litterfall from inventory plots across the Amazon region and other neotropical ecosystems. These data were used to train two machine-learning models and to evaluate model performance on reproducing stem growth and litterfall rates. The models utilized multiple climatological variables and other geospatial datasets (terrain, soil and vegetation properties) as explanatory variables. The output consisted of monthly estimates of leaf litterfall (R2= 0.71, NRMSE = 9.4 %) and stem growth (R2= 0.54, NRMSE = 10.6 %) across the neotropics from 1982 to 2019 at a high spatial resolution (0.1∘). Modelled time series allow us to assess the impacts of the 2005 and 2015 droughts in the Amazon basin on regional scales. The more severe 2015 drought was estimated to have caused widespread declines in stem growth (−1.8σ), coinciding with enhanced leaf fall (+1.4σ), which were only locally apparent in 2005. Regions in the Amazon basin that flushed leaves at the onset of both droughts (+0.9σ∼+2.0σ) showed positive anomalies in remotely sensed enhanced vegetation index, while sun-induced fluorescence and vegetation optical depth were reduced. The previously observed counterintuitive response of canopy green-up during drought in the Amazon basin detected by many remote sensing analyses can therefore be a result of enhanced leaf flushing at the onset of a drought. The long-term estimates of leaf litterfall and stem growth point to a decline in stem growth and a simultaneous increase in leaf litterfall in the Amazon basin since 1982. These trends are associated with increased warming and drying of the Amazonian climate and could point to a further decline in the Amazon carbon sink strength.

Plant functional trait variation in tropical forests results from taxonomic differences in phylogeny and associated genetic differences, as well as, phenotypic plastic responses to the environment. Accounting for the underlying mechanisms driving plant functional trait variation is important for understanding the potential rate of change of ecosystems since trait acclimation via phenotypic plasticity is very fast compared to shifts in community composition and genetic adaptation. We here applied a statistical technique to decompose the relative roles of phenotypic plasticity, genetic adaptation, and phylogenetic constraints. We examined typically obtained plant functional traits, such as wood density, plant height, specific leaf area, leaf area, leaf thickness, leaf dry mass content, leaf nitrogen content, and leaf phosphorus content. We assumed that genetic differences in plant functional traits between species and genotypes increase with environmental heterogeneity and geographic distance, whereas trait variation due to plastic acclimation to the local environment is independent of spatial distance between sampling sites. Results suggest that most of the observed trait variation could not be explained by the measured environmental variables, thus indicating a limited potential to predict individual plant traits from commonly assessed parameters. However, we found a difference in the response of plant functional traits, such that leaf traits varied in response to canopy‐light regime and nutrient availability, whereas wood traits were related to topoedaphic factors and water availability. Our analysis furthermore revealed differences in the functional response of coexisting neotropical tree species, which suggests that endemic species with conservative ecological strategies might be especially prone to competitive exclusion under projected climate change., We applied a statistical technique to analyze the relative amount of variation within plant functional traits associated with (a) environmental heterogeneity and spatial distance, as well as (b) bioclimatic variables in response to canopy‐light regime and soil nutrient availability. We found that plant functional reaction norms to bioclimatic variables reflect differences in the eco‐evolutionary trajectory and associated ecological life‐history strategy between congeneric pairs of widespread and coexisting endemic neotropical tree species.

SummaryIn vast areas of the world, the growth of forests and vegetation is water-limited and plant survival depends on the ability to avoid catastrophic hydraulic failure. Therefore, it is remarkable that plants take high hydraulic risks by operating at water potentials (ψ) that induce partial failure of the water conduits (xylem). Here we present an eco-evolutionary optimality principle for xylem conduit design that explains this phenomenon.Based on the hypothesis that conductive efficiency and safety are optimally co-adapted to the environment, we derive a simple relationship between the intrinsic tolerance to negative water potential (ψ50) and the environmentally dependent minimum xylem ψ.This relationship is constrained by a physiological tradeoff between xylem conductivity and safety, which is relatively strong at the level of individual conduits although it may be weak at the whole sapwood level. The model explains observed variation in ψ50 both across a large number of species, and along the xylem path in two species. The larger hydraulic safety margin in gymnosperms compared to angiosperms is explained as an adaptation to the gymnosperms’ lower capacity to recover from conductivity loss.The constant xylem safety factor provides a powerful principle for simplifying and improving plant and vegetation models.

In many tropical lowland rain forests, topographic variation increases environmental heterogeneity, thus contributing to the extraordinary biodiversity of tropical lowland forests. While a growing number of studies have addressed effects of topographic differences on tropical insect communities at regional scales (e.g., along extensive elevational gradients), surprisingly little is known about topographic effects at smaller spatial scales. The present study investigates moth assemblages in a topographically heterogeneous lowland rain forest landscape, at distances of less than a few hundred meters, in the Golfo Dulce region (SW Costa Rica). Three moth lineages—Erebidae–Arctiinae (tiger and lichen moths), the bombycoid complex, and Geometridae (inchworm moths)—were examined by means of automatic light traps in three different forest types: creek forest, slope forest, and ridge forest. Altogether, 6,543 individuals of 419 species were observed. Moth assemblages differed significantly between the three forest types regarding species richness, total abundance, and species composition. Moth richness and abundance increased more than fourfold and eightfold from creek over slope to ridge forest sites. All three taxonomic units showed identical biodiversity patterns, notwithstanding their strong differences in multiple eco‐morphological traits. An indicator species analysis revealed that most species identified as characteristic were associated either with the ridge forest alone or with ridge plus slope forests, but very few with the creek forest. Despite their mobility, local moth assemblages are highly differentially filtered from the same regional species pool. Hence, variation in environmental factors significantly affects assemblages of tropical moth species at small spatial scales. Abstract in Spanish is available with online material.

In vast areas of the world, the growth of forests and vegetation is water-limited and plant survival depends on the ability to avoid catastrophic hydraulic failure. Therefore, it is surprising that plants take high hydraulic risks by operating at water potentials (ψ) that induce partial failure of the water conduits (xylem) 1, and which makes them susceptible to drought mortality under climate change 2. Here we present an eco-evolutionary optimality principle for xylem design that explains this phenomenon - xylem is adapted to maximize its effective conductivity. A simple relationship emerges between the xylem intrinsic tolerance to high negative water potential (ψ50) and the environmentally dependent minimum ψ, which explains observed patterns across and within species. The theory provides a fundamental conduit-level principle that complements previously described principles at higher organizational levels, such as hydraulic-network scaling and drought-avoidance behavior. The new optimality principle may be universally valid, from within-individuals to across-species, and thus improve our basic understanding of drought tolerance of plants and forests globally.

We present Plant-FATE, a trait-size-structured vegetation model in which the time evolution of the size distribution of multiple species is modelled using the McKendrick-von Foerster partial differential equation. In our model, trait structure allows for representing any number of functionally distinct species as points in trait space, while size structure allows for modelling competition for light. To account for the stomatal and biochemical responses of leaves to environmental conditions, including CO2 concentration, vapour pressure deficit, and soil moisture, Plant-FATE incorporates ‘P-hydro’, a unified model for stomatal conductance and photosynthetic capacity [Joshi, J., et al. (2020). Towards a unified theory of plant photosynthesis and hydraulics. bioRxiv 2020.12.17.423132]. To model the resource allocation of plants, Plant-FATE uses an extended version of the ‘T-model’, accounting for crown geometry. In Plant-FATE, the vertical light profile attenuated by the canopy can be (optionally) modelled as a continuous light profile or via the ‘perfect plasticity approximation’ (PPA). Plant-FATE also includes a simple model for the acclimation of the crown leaf area index and an empirically derived model of plant mortality. Here, we present initial results exploring the effect of different trait combinations on the demographics of individual trees and single-species stands. We also analyse the outcomes of pairwise competition between species differing in their traits. Our approach is a step towards developing an eco-evolutionary vegetation model (EEVM) capable of simulating the adaptive responses of biodiverse plant communities to changing environmental conditions.

Soil fertility and plant productivity are globally constrained by N availability. Proteins are the largest N reservoir in soils, and the cleavage of proteins into small peptides and amino acids has been shown to be the rate-limiting step in the terrestrial N cycle. However, we are still lacking a profound understanding of the environmental controls of this process. Here we show that integrated effects of climate and soil geochemistry drive protein cleavage across large scales. We measured gross protein depolymerization rates in mineral and organic soils sampled across a 4000 km long European transect covering a wide range of climates, geologies and land uses. Based on structural equation models we identified that soil organic N cycling was strongly controlled by substrate availability, e.g., by soil protein content. Soil geochemistry was a secondary predictor, by controlling protein stabilization mechanisms and protein availability. Precipitation was identified as the main climatic control on protein depolymerization, by affecting soil weathering and soil organic matter accumulation. In contrast, land use was a poor predictor of protein depolymerization. Our results highlight the need to consider geology and precipitation effects on soil geochemistry when estimating and predicting soil N cycling at large scales.

Background It is relatively unknown if and how seasonal fluctuations of tropical microbial activity affect soil nutrient availability. In tropical forests, nutrient economics are often considered to be centered around phosphorus, which might be a limiting factor to sustain crucial ecosystem processes, such as primary production and decomposition of organic material, thus in turn affecting microbial processes and associated nutrient dynamics of the forest ecosystem. Aims We investigate seasonal fluctuations in extracellular hydrolytic soil enzyme activities and soil nutrients and its relationship with precipitation and litterfall input, in a lowland tropical forest in the Central Amazon region. Methods We analyzed data obtained from monitoring microbial enzyme activity and nutrient dynamics in litter and soil and use stoichiometric enzyme theory and proportional vectors for assessing relative nutrient limitation throughout a year. Results Our results show that precipitation seasonality was driving leaf litterfall, which was subsequently synchronized with extracellular enzyme activities in soil, such that both litterfall and enzyme activities peaked during the dry season. Conclusions Our study indicates that soil extractable nutrient concentrations were positively related to microbial enzyme activities, which thus highlights the importance of soil microbial processes for nutrient cycling in this phosphorus limited ecosystem. Our results suggest that projected shifts in climate seasonality that result in longer and more pronounced dry seasons, might desynchronize seasonal patterns of aboveground nutrient input and belowground microbial activity, and thus leading to a decoupling of nutrient cycling in tropical forest ecosystems.

Purpose Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers. Methods We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations. Results Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion. Conclusions We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems.

Purpose The tropical phosphorus cycle and its relation to soil phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on abiotic and biotic processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity. Methods We analyzed intra-annual variation of tropical soil phosphorus pools using a modified Hedley sequential fractionation scheme. In addition, we measured litterfall, the mobilization of P from litter and soil extracellular phosphatase enzyme activity and tested their relation to fluctuations in P- fractions. Results Our results showed clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm. Conclusion We conclude that input of P by litter decomposition and potential soil extracellular phosphatase activity are the two main factors related to seasonal soil P fluctuations, and therefore the P economy in P impoverished soils. Organic soil P followed a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context.

Purpose. The tropical phosphorus-cycle and its impacts on phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on biological and physical processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity. Methods. We analyzed variation of standard tropical soil phosphorus pools over one year. In addition, we measured litterfall, its decomposition rates and soil extracellular phosphatase enzyme activity and tested their relation to the fluctuations in P-fractions. Results. Our results show clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition is positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm. Conclusion. We conclude that input of organic P forms by litter decomposition and organically produced phosphatases are the two main factors controlling seasonal soil P fluctuation, and therefore the P economy in P impoverished soils. Organic soil P follows a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context.

The future Earth is projected to experience elevated rainfall variability, with more frequent and intense droughts, as well as high-rainfall events. Increasing CO2 concentrations are expected to raise terrestrial gross primary productivity (GPP), whereas water stress is expected to lower GPP. Plant responses to water stress vary strongly with timescale, and plants adapted to different environmental conditions differ in their functional responses. Here, we embed a unified optimality-based theory of stomatal conductance and biochemical acclimation of leaves we have recently developed [Joshi, J. et al. (2020) Towards a unified theory of plant photosynthesis and hydraulics. bioRxiv 2020.12.17.423132] in an eco-evolutionary vegetation-modelling framework, with the goal to investigate emergent functional diversity and associated GPP impacts under different rainfall regimes.The model of photosynthesis used here simultaneously predicts the stomatal responses and biochemical acclimation of leaves to atmospheric and soil-moisture conditions. Using three hydraulic traits and two cost parameters, it successfully predicts the simultaneous declines in CO2 assimilation rate, stomatal conductance, and leaf photosynthetic capacity caused by drying soil. It also correctly predicts the responses of CO2 assimilation rate, stomatal conductance, leaf water potential, and leaf photosynthetic capacity to vapour pressure deficit, temperature, ambient CO2, light intensity, and elevation. Our model therefore captures the synergistic effects of atmospheric and soil drought, as well as of atmospheric CO2 changes, on plant photosynthesis and transpiration.We embed this model of photosynthesis and transpiration in a trait-height-patch structured eco-evolutionary vegetation model. This model accounts for allometric carbon allocation, height-structured competition for light, patch-structured successional dynamics, and coevolution of plant functional traits. It predicts functional species mixtures and emergent ecosystem properties under different environmental conditions. Using this model, we investigate the evolution of plant hydraulic strategies under different regimes of drought and rainfall variability. Our approach provides an eco-evolutionarily consistent framework to scale up the responses of plant communities from individual plants to ecosystems to provide ecosystem-level predictions of functional diversity, primary production, and plant water use, and could thus be used for reliable projections of the global carbon and water cycles under future climate scenarios.

Large amounts of carbon flow through tropical ecosystems every year, from which a part is sequestered in biomass through tree growth. However, the effects of ongoing warming and drying on tree growth and carbon sequestration in tropical forest is still highly uncertain. Field observations are sparse and limited to a few sites while remote sensing analysis shows diverging growth responses to past droughts that cannot be interpreted with confidence. To reconcile data from field observations and remote sensing, we collated in situ measurements of stem growth and leaf litterfall from inventory plots across the Neotropics. This data was used to train two machine learning models and to evaluate model performance on reproducing stem growth and litterfall rates. The models utilized multiple climatological variables and other geospatial datasets as explanatory variables. The output consisted of monthly estimates of leaf litterfall (R2 = 0.67, NRMSE = 9.5 %) and stem growth (R2 = 0.51, NRMSE = 11.2 %) across the neotropics from 1982 to 2019 at a high spatial resolution (0.1°). Modelled time series allowed to assess the impacts of the 2005 and 2015 droughts in the Amazon basin on regional scales. Both droughts were estimated to have caused widespread declines in stem growth (−0.6σ ~ −1.8σ), coinciding with enhanced leaf fall (+0.7σ ~ +0.9σ). Regions in the Amazon basin that flushed leaves at the onset of both droughts (+1.1σ ~ +1.9σ), showed positive anomalies in remotely sensed enhanced vegetation index, while sun-induced fluorescence and vegetation optical depth were reduced. The previously observed counterintuitive response of canopy green-up during drought in the Amazon basin detected by many remote sensing analyses can therefore be explained by enhanced leaf flushing at the onset of a drought. The long-term estimates of leaf litterfall and stem growth point to a decline of stem growth and a simultaneous but weaker increase in leaf litterfall in the Amazon basin since 1982 that is not observed in long-term inventory plots. These trends are associated with increased warming and drying of the Amazonian climate.

International audience; Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha(-1) year(-1)), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha(-1) year(-1)) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha(-1) year(-1)) and canopy leaching (22 kg ha(-1) year(-1)) were three times larger than internal nutrient recycling via litterfall (11 kg ha(-1) year(-1)). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest.

Currently applied dynamic vegetation models do not realistically represent forest ecosystem processes and thus are not able to reproduce in-situ observations of forest ecosystem responses to drought. This is due to the fact that models typically rely on plant functional types to forecast the functional response of vegetation to climate change and to anthropogenic disturbance. However, recent observations of divergent ecosystem responses between topographic forest sites, differing in the availability of water and nutrients, indicate that we should no longer rely on this outdated concept but rather should explore new avenues of representing vegetation dynamics and associated climate change response in next-generation approaches.Global climate change scenarios forecast increasing severity of climate extremes in association with El Niño–Southern Oscillation (ENSO). Such climate anomalies have been shown to affect forest ecosystem processes such as net primary productivity, which is determined by climate (precipitation, temperature, and light) and soil fertility (geology and topography). However, more recently it has been suggested that the impact of such climate fluctuations on forest productivity was strongly related to local site characteristics, which determined the sensitivity of forest ecosystem processes to climate anomalies.We propose a novel approach integrating in-situ observations with remotely sensed estimates of forest aboveground productivity for parameterization of next-generation vegetation models capable of forecasting realistic forest ecosystem responses under future scenarios. Our approach considers local site characteristics associated with topography and disturbance history, both of which determine the sensitivity of forest aboveground productivity to projected climate anomalies. Our results therefore should have crucial implications for management and restoration of forest ecosystems and could be used to refine estimates of forest C sink-strength under future scenarios.

The rapid rise in atmospheric CO2 concentration over the past century is unprecedented. It has unambiguously influenced Earth’s climate system and terrestrial ecosystems. Elevated atmospheric CO2 concentrations (eCO2) have induced an increase in biomass and thus, a carbon sink in forests worldwide. It is assumed that eCO2 stimulates photosynthesis and plant productivity and enhances water-use efficiency – the so-called CO2-fertilization effect, which may provide an important buffering effect for plants during adverse climate conditions. For these reasons, current global climate simulations consistently predict that tropical forests will continue to sequester more carbon in aboveground biomass, partially compensating human emissions and decelerating climate change by acting as a carbon sink. In contrast to model simulations, several lines of evidence point towards a decreasing carbon sink strength of the Amazon rainforest. Reliable predictions of eCO2 effects in the Amazon rainforest are hindered by a lack of process-based information gained from ecosystem scale eCO2 experiments. Here we report on baseline measurements from the Amazon Free Air CO2 Enrichment (AmazonFACE) experiment and preliminary results from open-top chamber (OTC) experiments with eCO2. After three months of eCO2, we find that understory saplings increased carbon assimilation by 17% (under light saturated conditions) and water use efficiency by 39% in the OTC experiment. We present our main hypotheses for the FACE experiment, and discuss our expectations on the potential driving processes for limiting or stimulating the Amazon rainforest carbon sink under eCO2. We focus on possible effects of eCO2 on carbon uptake and allocation, nutrient cycling, water-use and plant-herbivore interactions, which need to be implemented in dynamic vegetation models to estimate future changes of the Amazon carbon sink.

Species‐rich plant communities have been shown to be more productive and to exhibit increased long‐term soil organic carbon (SOC) storage. Soil microorganisms are central to the conversion of plant organic matter into SOC, yet the relationship between plant diversity, soil microbial growth, turnover as well as carbon use efficiency (CUE) and SOC accumulation is unknown. As heterotrophic soil microbes are primarily carbon limited, it is important to understand how they respond to increased plant‐derived carbon inputs at higher plant species richness (PSR). We used the long‐term grassland biodiversity experiment in Jena, Germany, to examine how microbial physiology responds to changes in plant diversity and how this affects SOC content. The Jena Experiment considers different numbers of species (1–60), functional groups (1–4) as well as functional identity (small herbs, tall herbs, grasses, and legumes). We found that PSR accelerated microbial growth and turnover and increased microbial biomass and necromass. PSR also accelerated microbial respiration, but this effect was less strong than for microbial growth. In contrast, PSR did not affect microbial CUE or biomass‐specific respiration. Structural equation models revealed that PSR had direct positive effects on root biomass, and thereby on microbial growth and microbial biomass carbon. Finally, PSR increased SOC content via its positive influence on microbial biomass carbon. We suggest that PSR favors faster rates of microbial growth and turnover, likely due to greater plant productivity, resulting in higher amounts of microbial biomass and necromass that translate into the observed increase in SOC. We thus identify the microbial mechanism linking species‐rich plant communities to a carbon cycle process of importance to Earth's climate system., Global Change Biology, 26 (2), ISSN:1354-1013, ISSN:1365-2486

Forest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world’s forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities., Measurement(s)above-ground biomass • organic materialTechnology Type(s)tree species census • measurement methodFactor Type(s)geographic location • tree speciesSample Characteristic - Environmentforest biomeSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.9850571

Tropical rainforests harbor exceptionally high biodiversity and store large amounts of carbon in vegetation biomass. However, regional variation in plant species richness and vegetation carbon stock can be substantial, and may be related to the heterogeneity of topoedaphic properties. Therefore, aboveground vegetation carbon storage typically differs between geographic forest regions in association with the locally dominant plant functional group. A better understanding of the underlying factors controlling tropical forest diversity and vegetation carbon storage could be critical for predicting tropical carbon sink strength in response to projected climate change. Based on regionally replicated 1-ha forest inventory plots established in a region of high geomorphological heterogeneity we investigated how climatic and edaphic factors affect tropical forest diversity and vegetation carbon storage. Plant species richness (of all living stems >10 cm in diameter) ranged from 69 to 127 ha−1 and vegetation carbon storage ranged from 114 to 200 t ha−1. While plant species richness was controlled by climate and soil water availability, vegetation carbon storage was strongly related to wood density and soil phosphorus availability. Results suggest that local heterogeneity in resource availability and plant functional composition should be considered to improve projections of tropical forest ecosystem functioning under future scenarios. Las selvas tropicales albergan una biodiversidad excepcionalmente alta y almacenan grandes cantidades de carbono en la biomasa de la vegetación. Sin embargo, la variación regional en la riqueza de especies de plantas y las existencias de carbono de la vegetación puede ser sustancial y puede estar relacionada con la heterogeneidad de las propiedades topoedáficas. Por lo tanto, el almacenamiento de carbono de la vegetación aérea normalmente difiere entre las regiones forestales geográficas en asociación con el grupo funcional de plantas localmente dominante. Una mejor comprensión de los factores subyacentes que controlan la diversidad de los bosques tropicales y el almacenamiento de carbono de la vegetación podría ser fundamental para predecir la fuerza de los sumideros de carbono tropical en respuesta al cambio climático proyectado. Con base en parcelas de inventario forestal de 1 ha replicadas regionalmente establecidas en una región de alta heterogeneidad geomorfológica, investigamos cómo los factores climáticos y edáficos afectan la diversidad de los bosques tropicales y el almacenamiento de carbono de la vegetación. La riqueza de especies de plantas (de todos los tallos vivos> 10 cm de diámetro) varió de 69 a 127 ha - 1 y el almacenamiento de carbono de la vegetación varió de 114 a 200 t ha - 1. Si bien la riqueza de especies de plantas estuvo controlada por el clima y la disponibilidad de agua del suelo, la vegetación El almacenamiento de carbono estaba fuertemente relacionado con la densidad de la madera y la disponibilidad de fósforo en el suelo. Los resultados sugieren que se debe considerar la heterogeneidad local en la disponibilidad de recursos y la composición funcional de las plantas para mejorar las proyecciones del funcionamiento del ecosistema forestal tropical en escenarios futuros. International Institute for Applied Systems Analysis, Austria Universidad de Costa Rica University of Antwerp, Belgium Universidad Nacional, Costa Rica University of Vienna, Austria University of Natural Resources and Life Sciences, Austria Universidad de Salamanca, España Nanyang Technological University, Singapore Cardiff University, United Kingdom Coordenação de Dinâmica Ambiental, Brasil Technical University of Munich, Germany University Park, United Kingdom Escuela de Ciencias Ambientales

Plants and vegetation play a critical-but largely unpredictable-role in global environmental changes due to the multitude of contributing processes at widely different spatial and temporal scales. In this Perspective, we explore approaches to master this complexity and improve our ability to predict vegetation dynamics by explicitly taking account of principles that constrain plant and ecosystem behaviour: natural selection, self-organization and entropy maximization. These ideas are increasingly being used in vegetation models, but we argue that their full potential has yet to be realized. We demonstrate the power of natural selection-based optimality principles to predict photosynthetic and carbon allocation responses to multiple environmental drivers, as well as how individual plasticity leads to the predictable self-organization of forest canopies. We show how models of natural selection acting on a few key traits can generate realistic plant communities and how entropy maximization can identify the most probable outcomes of community dynamics in space- and time-varying environments. Finally, we present a roadmap indicating how these principles could be combined in a new generation of models with stronger theoretical foundations and an improved capacity to predict complex vegetation responses to environmental change.Integrating natural selection and other organizing principles into next-generation vegetation models could render them more theoretically sound and useful for earth system applications and modelling climate impacts.

Grassland management can modify soil microbial carbon (C) and nitrogen (N) cycling, affecting the resistance to extreme weather events, which are predicted to increase in frequency and magnitude in the near future. However, effects of grassland management on microbial C and N cycling and their responses to extreme weather events, such as droughts and heatwaves, have rarely been tested in a combined approach. We therefore investigated whether grassland management affects microbial C and N cycling responses to drought and temperature manipulation. We collected soils from in situ drought experiments conducted in an extensively managed and an abandoned mountain grassland and incubated them at two temperature levels. We measured microbial respiration and substrate incorporation, as well as gross rates of organic and inorganic N cycling to estimate microbial C and N use efficiencies (CUE and NUE). The managed grassland was characterized by lower microbial biomass, lower fungi to bacteria ratio, and higher microbial CUE, but only slightly different microbial NUE. At both sites drought induced a shift in microbial community composition driven by an increase in Gram-positive bacterial abundance. Drought significantly reduced C substrate respiration and incorporation by microbes at both sites, while microbial CUE remained constant. In contrast, drought increased gross rates of N mineralization at both sites, whereas gross amino acid uptake rates only marginally changed. We observed a significant direct, as well as interactive effect between land management and drought on microbial NUE. Increased temperatures significantly stimulated microbial respiration and reduced microbial CUE independent of drought or land management. Although microbial N processing rates showed no clear response, microbial NUE significantly decreased at higher temperatures. In summary in our study, microbial CUE, in particular respiration, is more responsive to temperature changes. Although N processing rates were stronger responding to drought than to temperature microbial NUE was affected by both drought and temperature increase. We conclude that direct effects of drought and heatwaves can induce different responses in soil microbial C and N cycling similarly in the studied land management systems.

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional-landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1-ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/ very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands Universidad Nacional, Costa Rica Universidad de Vienna, Austria International Institute for Applied Systems Analysis, Austria Universidad de Costa Rica, Costa Rica Universidad de Salamanca, España Escuela de Ciencias Biológicas

Historic mining in the Eastern Alps has left us with a legacy of numerous spoil heaps hosting specific, metal tolerant vegetation. Such habitats are characterized by elevated concentrations of toxic elements but also by high irradiation, a poorly developed substrate or extreme pH of the soil. This study investigates the distribution of vascular plants, mosses and lichens on a copper spoil heap on the ore bearing Knappenberg formed by Prebichl Layers and Werfener Schist in Lower Austria. It serves as a model for discriminating between various ecological traits and their effects on vegetation. Five distinct clusters were distinguished: (1) The bare, metal rich Central Spoil Heap was only colonised by highly resistant specialists. (2) The Northern and (3) Southern Peripheries contained less copper; the contrasting vegetation was best explained by the different microclimate. (4) A forest over acidic bedrock hosted a vegetation overlapping with the periphery of the spoil heap. (5) A forest over calcareous bedrock was similar to the spoil heap with regard to pH and humus content but hosted a vegetation differing strongly to all other habitats. Among the multiple toxic elements at the spoil heap, only Cu seems to exert a crucial influence on the vegetation pattern. Besides metal concentrations, irradiation, humidity, humus, pH and grain size distribution are important for the establishment of a metal tolerant vegetation. The difference between the species poor Northern and the diverse Southern Periphery can be explained by the microclimate rather than by the substrate. All plant species penetrating from the forest into the periphery of the spoil heap originate from the acidic but not from the calcareous bedrock.

Drought stress hampers plant energy and biomass production; however it is still unknown how internal C:N balance and rhizobial symbiosis impact on plant response to water limitation. Here, the effect of differential optimal nitrogen nutrition and root nodule symbiosis on drought stress and rehydration responses of Medicago truncatula was assessed.Two groups of plants were nodulated with Sinorhizobium medicae or Sinorhizobium meliloti — differing in the performance of N fixation; the third group grew in a rhizobia-free medium and received mineral nitrogen fertilizer. In addition to growth analyses, physiological and molecular responses of the two systems were studied using ionomic, metabolomic and proteomic techniques.We found a significant delay in drought-induced leaf senescence in nodulated relative to non-nodulated plants, independent of rhizobial strain and uncoupled from initial leaf N content. The major mechanisms involved are increased concentrations of potassium and shifts in the carbon partitioning between starch and sugars under well-watered conditions, as well as the enhanced allocation of reserves to osmolytes during drought. Consequently, nodulated plants recovered more effectively from drought, relative to non-nodulated M. truncatula. Proteomic data suggest that phytohormone interactions and enhanced translational regulation play a role in increased leaf maintenance in nodulated plants during drought.

The Golfo Dulce region located in southwestern Costa Rica represents one of the remnant global biodiversity hotspots containing the largest Pacific lowland tropical forest in Central America. Recent biogeographical analyses revealed a close relation of taxonomic tree species composition to northern South America. However, the underlying factors leading to the extraordinary taxonomic richness of the region have so far remained elusive. In this study, we analyzed the composition of tropical forest plant communities (trees, lianas and palms with a diameter at breast height ≥10 cm) occurring in one-hectare permanent forest inventory plots. To that end, we established 20 forest sites across the Golfo Dulce region, i.e. 5 geographic locations each comprising 4 forest habitat types in ridge, slope and ravine positions, as well as in secondary forest stands. Our study highlights the oligarchic dominance of tropical forest plant communities in the Golfo Dulce region, and further suggests that plant species composition is associated with topography, disturbance history and edaphic properties. The finding that oligarchic and rare species are affected by environmental filtering has important implications for assessment and modeling of important ecosystem functions, such as carbon storage and productivity, as well as nutrient cycling and trophic interactions and thus could potentially improve biodiversity conservation and management strategies. Die Golfo Dulce-Region im Südwesten von Costa Rica ist einer der letzten globalen Biodiversitäts-Hotspots mit dem größten verbliebenen tropischen Wald im pazifischen Tiefland in Mittelamerika. Jüngste biogeografische Analysen der taxonomischen Baumartenzusammensetzung zeigten eine enge Beziehung zu den Pflanzengesellschaften Südamerikas. Die zugrundeliegenden Faktoren, die zu dem außerordentlichen taxonomischen Reichtum der Region führten, sind jedoch bislang schwer fassbar. In dieser Studie haben wir die Zusammensetzung der tropischen Vegetation (Bäume, Lianen und Palmen mit einem Durchmesser in Brusthöhe ≥ 10 cm) auf 20 Inventarflächen von jeweils 1ha Größe (5 geografische Standorte mit jeweils 4 Habitatstypen in Kamm-, Hang- und Schlucht- Position, sowie einem Sekundärwald) analysiert. Unsere Studie beschreibt die Dominanz häufiger tropischer Pflanzenarten und legt nahe, dass die Zusammensetzung der Vegetation mit der Topographie, der Störungsgeschichte und den edaphischen Eigenschaften zusammenhängt. Die Feststellung, dass die Zusammensetzung von sowohl häufig vorkommenden als auch eher seltenen, Großteils endemischen Arten von denselben Umweltfaktoren beeinflusst wird, birgt interessante Erkenntnisse über wichtige Ökosystemfunktionen wie die Kohlenstoffspeicherung und die Produktivität des Ökosystems und könnte somit helfen Strategien zur Erhaltung und Bewirtschaftung der Artenvielfalt in tropischen Ökosystemen zu entwickeln. UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biología

Tropical vegetation biomass represents a key component of the carbon stored in global forest ecosystems. Estimates of aboveground biomass commonly rely on measurements of tree size (diameter and height) and then indirectly relate, via allometric relationships and wood density, to biomass sampled from a relatively small number of harvested and weighed trees. Recently, however, novel in situ remote sensing techniques have been proposed, which may provide nondestructive alternative approaches to derive biomass estimates. Nonetheless, we still lack knowledge of the measurement uncertainties, as both the calibration and validation of estimates using different techniques and instruments requires consistent assessment of the underlying errors. To that end, we investigate different approaches estimating the tropical aboveground biomass in situ. We quantify the total and systematic errors among measurements obtained from terrestrial light detection and ranging (LiDAR), hypsometer-based trigonometry, and traditional forest inventory. We show that laser-based estimates of aboveground biomass are in good agreement (< 10% measurement uncertainty) with traditional measurements. However, relative uncertainties vary among the allometric equations based on the vegetation parameters used for parameterization. We report the error metrics for measurements of tree diameter and tree height and discuss the consequences for estimated biomass. Despite methodological differences detected in this study, we conclude that laser-based electronic devices could complement conventional measurement techniques, thereby potentially improving estimates of tropical vegetation biomass. © 2019 by the authors.

One of the best-known general patterns in island biogeography is the species-isolation relationship (SIR), a decrease in the number of native species with increasing island isolation that is linked to lower rates of natural dispersal and colonization on remote oceanic islands. However, during recent centuries, the anthropogenic introduction of alien species has increasingly gained importance and altered the composition and richness of island species pools. We analyzed a large dataset for alien and native plants, ants, reptiles, mammals, and birds on 257 (sub) tropical islands, and showed that, except for birds, the number of naturalized alien species increases with isolation for all taxa, a pattern that is opposite to the negative SIR of native species. We argue that the reversal of the SIR for alien species is driven by an increase in island invasibility due to reduced diversity and increased ecological naiveté of native biota on the more remote islands. published

International audience; Comparing model output and observed data is an important step for assessing model performance and quality of simulation results. However, such comparisons are often hampered by differences in spatial scales between local point observations and large-scale simulations of grid cells or pixels. In this study, we propose a generic approach for a pixel-to-point comparison and provide statistical measures accounting for the uncertainty resulting from landscape variability and measurement errors in ecosystem variables. The basic concept of our approach is to determine the statistical properties of small-scale (within-pixel) variability and observational errors, and to use this information to correct for their effect when large-scale area averages (pixel) are compared to small-scale point estimates. We demonstrate our approach by comparing simulated values of aboveground biomass, woody productivity (woody net primary productivity, NPP) and residence time of woody biomass from four dynamic global vegetation models (DGVMs) with measured inventory data from permanent plots in the Amazon rainforest, a region with the typical problem of low data availability, potential scale mismatch and thus high model uncertainty. We find that the DGVMs under-and overestimate aboveground biomass by 25 % and up to 60 %, respectively. Our comparison metrics provide a quantitative measure for model-data agreement and show moderate to good agreement with the region-wide spatial biomass pattern detected by plot observations. However , all four DGVMs overestimate woody productivity and underestimate residence time of woody biomass even when accounting for the large uncertainty range of the observational data. This is because DGVMs do not represent the Published by Copernicus Publications on behalf of the European Geosciences Union. 5204 A. Rammig et al.: Pixel-to-point comparison for simulated large-scale ecosystem properties relation between productivity and residence time of woody biomass correctly. Thus, the DGVMs may simulate the correct large-scale patterns of biomass but for the wrong reasons. We conclude that more information about the underlying processes driving biomass distribution are necessary to improve DGVMs. Our approach provides robust statistical measures for any pixel-to-point comparison, which is applicable for evaluation of models and remote-sensing products.

Bryophytes are well-studied model systems for the investigation of uptake mechanisms and pollutant tolerance of plants. The moss Physcomitrella patens is among the most intensively studied organisms with regard to physiological and cellular pathways; however, direct ecological studies on metal stress are rare in this species. We conducted growth experiments on copper and zinc containing media for five and ten weeks, respectively in order to investigate the element and anion dependent metal uptake by energy—dispersive X-ray spectroscopy on a scanning electron microscope. We compared the uptake of metals to the growth and morphology of leaves and protonemata of P. patens. The metal content of both tissues was strongly correlated with availability of free metal cations. Differences between copper and zinc uptake included the limitation of zinc uptake found after five weeks for both tissues. No further sequestration of metal occurred after week five. The content of up to 1.3 wt% zinc and 0.4 wt% copper in the dry biomass correlated negatively to leafy gametophyte growth and to cell length in both tissues. No such correlation to protonema growth or cell width was found. The shortening of protonema cells exposed to zinc did not necessarily lead to decreased protonemal growth. This indicates a compensation of the shorter cells by increased cell division of the protonema filaments.

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained

The productivity of tropical forests is driven by climate (precipitation, temperature, and light) and soil fertility (geology and topography). While large-scale drivers of tropical productivity are well established, knowledge on the sensitivity of tropical lowland net primary production to climate anomalies remains scarce. We here analyze seven consecutive years of monthly recorded tropical forest aboveground net primary production (ANPP) in response to a recent El Nino–Southern Oscillation (ENSO) anomaly. The ENSO transition period resulted in increased temperatures and decreased precipitation during the El Nino dry period, causing a decrease in ANPP. However, the subsequent La Nina wet period caused strong increases in ANPP such that drought-induced reductions were overcompensated. Most strikingly, the climatic controls differed between canopy production (CP) and wood production (WP). Whereas CP showed strong seasonal variation but was not affected by ENSO, WP decreased significantly in response to a 3°C increase in annual maximum temperatures during the El Nino period but subsequently recovered to above predrought levels during the La Nina period. Moreover, the climate sensitivity of tropical forest ANPP components was affected by local topography (water availability) and disturbance history (species composition). Our results suggest that projected increases in temperature and dry season length could impact tropical carbon sequestration by shifting ANPP partitioning toward decreased WP, thus decreasing the carbon storage of highly productive lowland forests. We conclude that the impact of climate anomalies on tropical forest productivity is strongly related to local site characteristics and will therefore likely prevent uniform responses of tropical lowland forests to projected global changes.

The Schwarzwand is a unique hygric, Cu-contaminated habitat formed by mining activities from the 16th to 18th century. Today, a large spoil heap and several creeks fed by Cu-rich mine drainage are present. The vegetation of the Schwarzwand differs clearly from the surrounding subalpine forests. It is by no means impoverished but rather a hotspot of biodiversity. Interestingly, most of the Cu precipitates within the Schwarzwand and the creeks leave the Schwarzwand virtually clean. This study maps the distribution of Cu within the Schwarzwand and within selected vascular plants, moss and microorganisms and correlates them with water and soil chemistry in order to identify the sinks of Cu and to elucidate the remarkable capability of the Schwarzwand for natural attenuation. Two types of water could be distinguished, one acidic precipitating limonite with a constant Cu content of about 0.6 mg L−1, and one circumneutral, which decreases far more rapidly in Cu content than would be expected due to chemical considerations. A dense microbial mat covering most of the bed of the circumneutral creeks could be identified as the main sink. It consists of the cyanobacterium Phormidium sp. and retains Cu both by adsorption to mucilaginous sheaths and by precipitation as secondary minerals such as sampleite. Layers of dead biofilm can be found covered by a few centimetres of soil at the banks of the circumneutral creeks; the extremely high concentration and the low solubility of Cu in this soil indicates permanent immobilisation of the metals. High concentrations of Cu were also found in mosses of the family Bryaceae which, however, play a negligible role for the metal retention of the habitat due to their low biomass. The retention of Cu within the Schwarzwand is a remarkable example of the sustainable self-cleaning of a contaminated habitat which takes place without any human intervention. The artificial establishment of microbial communities similar to the Schwarzwand could result in cheap and sustainable strategies for the remediation of suitable metal-contaminated waters.

Analysis of disturbance effects on multiple microbial processes elucidates response of biogeochemical cycling to climate extremes., Predicted changes in the intensity and frequency of climate extremes urge a better mechanistic understanding of the stress response of microbially mediated carbon (C) and nutrient cycling processes. We analyzed the resistance and resilience of microbial C, nitrogen (N), and phosphorus (P) cycling processes and microbial community composition in decomposing plant litter to transient, but severe, temperature disturbances, namely, freeze-thaw and heat. Disturbances led temporarily to a more rapid cycling of C and N but caused a down-regulation of P cycling. In contrast to the fast recovery of the initially stimulated C and N processes, we found a slow recovery of P mineralization rates, which was not accompanied by significant changes in community composition. The functional and structural responses to the two distinct temperature disturbances were markedly similar, suggesting that direct negative physical effects and costs associated with the stress response were comparable. Moreover, the stress response of extracellular enzyme activities, but not that of intracellular microbial processes (for example, respiration or N mineralization), was dependent on the nutrient content of the resource through its effect on microbial physiology and community composition. Our laboratory study provides novel insights into the mechanisms of microbial functional stress responses that can serve as a basis for field studies and, in particular, illustrates the need for a closer integration of microbial C-N-P interactions into climate extremes research.