Microorganisms are vital in mediating the earth’s biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: ‘When do we need to understand microbial community structure to accurately predict function?’ We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.

Perennial rivers and streams make a disproportionate contribution to global carbon (C)cycling. However, the contribution of intermittent rivers and ephemeral streams, which

Much effort has been devoted to better understanding the effects of environment and biodiversity on ecosystem functioning. However, few studies have moved beyond measuring biodiversity as species richness of a single group and/or focusing on a single ecosystem function. While there is a growing recognition that along environmental gradients, the compositional turnover of multiple trophic groups influences not only productivity but multiple ecosystem functions, we do not know yet which components of multi‐trophic β‐diversity influence which ecosystem functions. Here, we captured the biodiversity found in soils using environmental DNA to study total soil multi‐trophic β‐diversity (between all taxa regardless of their trophic group association), horizontal β‐diversities (β‐diversities within trophic groups) and vertical β‐diversity (β‐diversity across trophic groups) along a 1,000 m elevational gradient in the French Alps. Using path analyses, we quantified how these β‐diversity components mediate the effects of environmental turnover on the turnover of multiple ecosystem functions (i.e. productivity, N‐cycling, N‐leaching) and overall multifunctionality. While we found a strong direct effect of soil properties on the turnover of multiple ecosystem functions, we also found an indirect effect of climate and soil properties through multi‐trophic β‐diversity. More specifically, only total multi‐trophic β‐diversity and the horizontal β‐diversity of saprophytic fungi were strongly related to the turnover of multifunctionality and, to a lower extent, the turnover of productivity and N‐cycling. Our results suggest that decomposition processes and resulting nutrient availability are key to understand how ecosystem functions change along soil properties and climatic gradients in alpine ecosystems. By demonstrating how saprophytic fungi and their associated trophic groups can offset the direct responses of multiple ecosystem functions to environmental change, our study highlights the paramount importance of multi‐trophic diversity for better understanding ecosystem multifunctionality in a changing world. A free Plain Language Summary can be found within the Supporting Information of this article.

-Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their interactions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydrological exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic *Corresponding author: pierre.marmonier@univ-lyon1.frArticle published by EDP Sciences Ann. Limnol. -Int. J. Lim. 48 (2012) [253][254][255][256][257][258][259][260][261][262][263][264][265][266] Available online at: Ó EDP Sciences, 2012 www.limnology-journal.org DOI: 10.1051/limn/2012009 zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies.

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%–98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.

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1. Trait-based approaches provide a framework to understand the role of functional biodiversity on ecosystem functioning under global change. While plant traits have been reported as potential drivers of soil microbial community composition and resilience, studies directly assessing microbial traits are scarce, limiting our mechanistic understanding of ecosystem functioning.2. We used microbial biomass and enzyme stoichiometry, and mass-specific enzymes activity as proxies of microbial community-weighted mean (CWM) traits, to infer trade-offs in microbial strategies of resource use with cascading effects on ecosystem resilience. We simulated a drought event on intact plant-soil mesocosms extracted from mountain grasslands along a management intensity gradient.Ecosystem processes and properties related to nitrogen cycling were quantified before, during and after drought to characterize ecosystem resilience.3. Soil microbial CWM traits and ecosystem resilience to drought were strongly influenced by grassland type. Structural equation modelling revealed a cascading effect from management to ecosystem resilience through modifications in soil nutrients, and plant and microbial CWM traits. Overall, our results depict a shift from high investment in extracellular enzymes in nutrient-poor soils (oligotrophic strategy), to a copiotrophic strategy with low microbial biomass N:P and low investment in extracellular enzymes associated with exploitative plant traits in nutrient-rich soils.4. Microbial CWM traits responses to management intensity were highly related to ecosystem resilience. Microbial communities with a copiotrophic strategy had lower resistance but higher recovery to drought, while microbial communities with an oligotrophic strategy showed the opposite responses. The unexpected trade-off between plant and microbial resistance suggested that the lower resistance of copiotrophic microbial communities enabled plant resistance to drought. Synthesis.Grassland management has cascading effects on ecosystem resilience through its combined effects on soil nutrients and plant traits propagating to microbial traits and resilience. We suggest that intensification of permanent grassland management and associated increases in soil nutrient availability decreased | 877 Journal of Ecology PITON eT al. S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Piton G, Legay N, Arnoldi C, Lavorel S, Clément J-C, Foulquier A. Using proxies of microbial community-weighted means traits to explain the cascading effect of management intensity, soil and plant traits on ecosystem resilience in mountain grasslands.