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Aim Soil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions are linked to tree species composition and diversity, there has been no comprehensive study of the generality or context dependence of these relationships. Here, we examine tree diversity–soil microbial biomass and respiration relationships across environmental gradients using a global network of tree diversity experiments. Location Boreal, temperate, subtropical and tropical forests. Time period 2013. Major taxa studied Soil microorganisms. Methods Soil samples collected from 11 tree diversity experiments were used to measure microbial respiration, biomass and respiratory quotient using the substrate-induced respiration method. All samples were measured using the same analytical device, method and procedure to reduce measurement bias. We used linear mixed-effects models and principal components analysis (PCA) to examine the effects of tree diversity (taxonomic and phylogenetic), environmental conditions and interactions on soil microbial properties. Results Abiotic drivers, mainly soil water content, but also soil carbon and soil pH, significantly increased soil microbial biomass and respiration. High soil water content reduced the importance of other abiotic drivers. Tree diversity had no effect on the soil microbial properties, but interactions with phylogenetic diversity indicated that the effects of diversity were context dependent and stronger in drier soils. Similar results were found for soil carbon and soil pH. Main conclusions Our results indicate the importance of abiotic variables, especially soil water content, for maintaining high levels of soil microbial functions and modulating the effects of other environmental drivers. Planting tree species with diverse water-use strategies and structurally complex canopies and high leaf area might be crucial for maintaining high soil microbial biomass and respiration. Given that greater phylogenetic distance alleviated unfavourable soil water conditions, reforestation efforts that account for traits improving soil water content or select more phylogenetically distant species might assist in increasing soil microbial functions.

Aim: Theoretical, experimental and observational studies have shown that biodiversity–ecosystem functioning (BEF) relationships are influenced by functional community structure through two mutually non-exclusive mechanisms: (1) the dominance effect (which relates to the traits of the dominant species); and (2) the niche partitioning effect [which relates to functional diversity (FD)]. Although both mechanisms have been studied in plant communities and experiments at small spatial extents, it remains unclear whether evidence from small-extent case studies translates into a generalizable macroecological pattern. Here, we evaluate dominance and niche partitioning effects simultaneously in grassland systems world-wide.Location: Two thousand nine hundred and forty-one grassland plots globally.Time period: 2000–2014.Major taxa studied: Vascular plants.Methods: We obtained plot-based data on functional community structure from the global vegetation plot database “sPlot”, which combines species composition with plant trait data from the “TRY” database. We used data on the community-weighted mean (CWM) and FD for 18 ecologically relevant plant traits. As an indicator of primary productivity, we extracted the satellite-derived normalized difference vegetation index (NDVI) from MODIS. Using generalized additive models and deviation partitioning, we estimated the contributions of trait CWM and FD to the variation in annual maximum NDVI, while controlling for climatic variables and spatial structure.Results: Grassland communities dominated by relatively tall species with acquisitive traits had higher NDVI values, suggesting the prevalence of dominance effects for BEF relationships. We found no support for niche partitioning for the functional traits analysed, because NDVI remained unaffected by FD. Most of the predictive power of traits was shared by climatic predictors and spatial coordinates. This highlights the importance of community assembly processes for BEF relationships in natural communities.Main conclusions: Our analysis provides empirical evidence that plant functional community structure and global patterns in primary productivity are linked through the resource economics and size traits of the dominant species. This is an important test of the hypotheses underlying BEF relationships at the global scale.

Plant–soil feedback (PSF) has gained attention as a mechanism promoting plant growth and coexistence. However, most PSF research has measured monoculture growth in greenhouse conditions. Translating PSFs into effects on plant growth in field communities remains an important frontier for PSF research. Using a 4‐year, factorial field experiment in Jena, Germany, we measured the growth of nine grassland species on soils conditioned by each of the target species (i.e., 72 PSFs). Plant community models were parameterized with or without these PSF effects, and model predictions were compared to plant biomass production in diversity–productivity experiments. Plants created soils that changed subsequent plant biomass by 40%. However, because they were both positive and negative, the average PSF effect was 14% less growth on “home” than on “away” soils. Nine‐species plant communities produced 29 to 37% more biomass for polycultures than for monocultures due primarily to selection effects. With or without PSF, plant community models predicted 28%–29% more biomass for polycultures than for monocultures, again due primarily to selection effects. Synthesis: Despite causing 40% changes in plant biomass, PSFs had little effect on model predictions of plant community biomass across a range of species richness. While somewhat surprising, a lack of a PSF effect was appropriate in this site because species richness effects in this study were caused by selection effects and not complementarity effects (PSFs are a complementarity mechanism). Our plant community models helped us describe several reasons that even large PSF may not affect plant productivity. Notably, we found that dominant species demonstrated small PSF, suggesting there may be selective pressure for plants to create neutral PSF. Broadly, testing PSFs in plant communities in field conditions provided a more realistic understanding of how PSFs affect plant growth in communities in the context of other species traits., Plant–soil feedbacks have gained attention as a mechanism of plant growth and coexistence, yet most plant–soil feedback research continues to be performed in greenhouse conditions. At the end of a 4‐year field experiment, plants created soils that changed subsequent plant growth by 37%, yet these relatively large effects had little effect on plant community growth because some feedbacks were positive and others negative and because feedbacks for the dominant species were small. Research highlights the need to test the consequences of plant–soil feedbacks in plant communities.

Though it is well established that species composition affects ecosystem function, the way in which species combine to control overall ecosystem functioning is still debated. In experimental mesocosms, we planted three functionally distinct dry-heath species in varying proportions and measured multiple ecosystem properties related to nutrient cycling and carbon storage (hereafter functions). Overall ecosystem functioning was described as the main axes of variation in ecosystem functioning (functional space) and the proportion of ecosystem functions at high levels; for example, fast carbon and nutrient cycling (cluster-based multifunctionality). The first functional space axis, related to nitrogen availability, was driven by plant species abundance, particularly that of legumes, which strongly affected many individual functions. The second, related to total plant biomass and woodiness, was mostly driven by the abundance of dwarf shrubs. Similarly, cluster-based multifunctionality was related to the initial abundance of all species, but particularly the legume. Interactions between species also affected ecosystem multifunctionality, but these effects were smaller in magnitude. These results indicate that species interactions could play a secondary role to species abundance and identity in driving the overall ecosystem functioning of heathlands, but also that axes of variation in functional space are clearly linked to plant functional composition.

1. Theory predicts that a large fraction of phytochemical diversity—the richness of individual chemical compounds produced by plants—governs the complexity of interactions between plants and their herbivores. While the effect of specific classes of chemical compounds on plant resistance against herbivores has been largely documented, the effect of community-level variation in phytochemical diversity on plant–herbivore interactions has so far received minimal consideration. 2. We hypothesized that plant communities bearing on average higher levels of phytochemical diversity should sustain lower herbivory rates, overall. Yet, the magnitude of this effect could vary across different environmental conditions, potentially because of climate-mediated effects on phytochemical production and changes in herbivore community richness and composition. 3. To address these hypotheses, we used previous knowledge of species-level phytochemical make-up for more than 400 plant species of the Swiss Alps. Using common garden experiments, we estimated season-wide herbivore damage on low (average 3,500 unique molecules) and high (average 4,500 unique molecules) phytochemical diversity plant communities that were planted in the colline, mountain and alpine vegetation sites along two elevation transects in the Alps. 4. We found that high phytochemical diversity plant communities showed reduced levels of herbivore damage in the colline (low elevation) sites, but this pattern reversed in the alpine (high elevation) sites. Our results suggest that the outcome of phytochemical diversity on plant–herbivore interactions depends on the characteristics of the local herbivore communities, together with trade-offs between chemical defences and other plant traits (i.e. physical defences and plant palatability). 5. Synthesis. Phytochemical diversity is a key component of functional diversity, influencing community composition and dynamics. We show that the effect of phytochemical diversity on herbivory is environmental-dependent, generating ecological switches when moving from low to high elevation. Through upward movement of plants under climate change, phytochemical community structure will be likely modified, ultimately disrupting local community assembly processes. ISSN:0022-0477

The diversity-invasibility hypothesis (Elton, 1958) states that there is a negative relationship between the diversity of an ecological community and the ability of invaders to establish in it. This hypothesis has been the subject of many experiments in ecology, with the majority of experimental results supporting it (Levine et al. 2002). More recently, this hypothesis has been extended to microorganisms, with a suite of microbial ecology experiments emerging in the past ~20 years that test the diversity-invasibility hypothesis in experimental microbial communities. However, the results of these experiments have not been systematically reviewed and meta-analysed, and thus consensus about diversity-invasibility in microbial communities is lacking. Here we set out a protocol for a systematic review and meta-analysis to synthesise the evidence for diversity-invasibility relationships in microbial ecology. The study will help elucidate the importance of microbial diversity for the stability of microbial communities to invasion, which may have relevance for conserving the integrity of microbial communities that perform ecosystem services and/or protect hosts from pathogen invasion.

The biodiversity crisis has increased interest in understanding the role of biodiversity for ecosystem functioning. Functional traits are often used to infer ecosystem functions to increase our understanding of these relationships over larger spatial scales. The links between specific traits and ecosystem functioning are, however, not always well established. We investigated how the choice of analyzing either individual species, selected modalities, or trait combinations affected the spatial patterns observed on a sandflat and how this was related to the natural variability in ecosystem functioning. A large dataset of 400 benthic macrofauna samples was used to explore distribution patterns. We hypothesized that (1) if multiple species (redundancy) represent a trait combination or a modality their spatial patterns would be smoothed out, and (2) the lost spatial variability within a trait combination or modality, due to the smoothing effect, would potentially affect their utility for predicting ecosystem functioning (tested on a dataset of 24 samples). We predicted that species would show heterogeneous small spatial patterns, while modalities and trait combinations would show larger and more homogeneous patterns because they would represent a collection of many distributions. If modalities and trait combinations are better predictors of ecosystem functioning than species, then the smoother spatial patterns of modalities and trait combinations would result in a more homogeneous landscape of ecosystem function and the number of species exhibiting specific traits would provide functional redundancy. Our results showed some smoothing of spatial patterns progressing from species through modalities to trait combinations, but generally spatial patterns reflected a few dominant key species. Moreover, some individual modalities and species explained more or equal proportions of the variance in the ecosystem functioning than the combined traits. The findings thus suggest that only some spatial variability is lost when species are combined into modalities and trait combinations and that a homogeneous landscape of ecosystem function is not likely., Functional traits are often used to infer ecosystem functioning across larger scales, but how do they reflect species distributions and how well do they actually explain the natural spatial variability in ecosystem functioning? This was examined with a rarely seen extensive dataset of benthic macrofauna samples and solute flux measurements across the sediment–water interface.

International audience; Understanding how ecosystems will respond to climate changes requires unravelling the network of functional responses and feedbacks among biodiversity, physicochemical environments, and productivity. These ecosystem components not only change over time but also interact with each other. Therefore, investigation of individual relationships may give limited insights into their interdependencies and limit ability to predict future ecosystem states. We address this problem by analyzing long-term (16-39 years) time series data from 10 aquatic ecosystems and using convergent cross mapping (CCM) to quantify the causal networks linking phytoplankton species richness, biomass, and physicochemical factors. We determined that individual quantities (e.g., total species richness or nutrients) were not significant predictors of ecosystem stability (quantified as long-term fluctuation of phytoplankton biomass); rather, the integrated causal pathway in the ecosystem network, composed of the interactions among species richness, nutrient cycling, and phytoplankton biomass, was the best predictor of stability. Furthermore, systems that experienced stronger warming over time had both weakened causal interactions and larger fluctuations. Thus, rather than thinking in terms of separate factors, a more holistic network view, that causally links species richness and the other ecosystem components, is required to understand and predict climate impacts on the temporal stability of aquatic ecosystems.

Long‐term grassland biodiversity experiments have shown that diversity effects on productivity tend to strengthen through time, as complementarity among coexisting species increases. But it remains less clear whether this pattern also holds for other ecosystems such as forests, and if so why.Here we explore whether diversity effects on tree growth change predictably during stand development in Finland's boreal forests. Using tree ring records from mature forests, we tested whether diameter growth trajectories of dominant tree species growing in mixture differed from those in monoculture. We then compared these results with data from the world's longest running tree diversity experiment, where the same combinations of species sampled in mature forests were planted in 1999.We found that diversity effects on tree growth strengthened progressively through time, only becoming significantly positive around 20 years after seedling establishment. This shift coincided with the period in which canopy closure occurs in these forests, at which time trees begin to interact and compete above‐ground. These temporal trends were remarkably consistent across different tree species sampled in mature forests, and broadly matched growth responses observed in the much younger experimental plots.Synthesis. Our results mirror those from grassland ecosystems and suggest that canopy closure is a key phase for promoting niche complementarity in diverse tree communities. They also provide a series of testable hypotheses for the growing number of tree diversity experiments that have been established in recent years.

Anthropogenic impacts on freshwater ecosystems cause critical losses of biodiversity that can in turn impair key processes such as decomposition and nutrient cycling. Forest streams are mainly subsidized by terrestrial organic detritus, so their functioning and conservation status can be altered by changes in forest biodiversity and composition, particularly if these changes involve the replacement of functional groups or the loss of key species. We examined this issue using a microcosm experiment where we manipulated plant functional diversity (FD) (monocultures and low-FD and high-FD mixtures, resulting from different combinations of deciduous and evergreen Quercus species) and the presence of a key species (Alnus glutinosa), all in presence and absence of detritivores, and assessed effects on litter decomposition, nutrient cycling, and fungal and detritivore biomass. We found (i) positive diversity effects on detritivore-mediated decomposition, litter nutrient losses and detritivore biomass exclusively when A. glutinosa was present; and (ii) negative effects on the same processes when microbially mediated and on fungal biomass. Most positive trends could be explained by the higher litter palatability and litter trait variability obtained with the inclusion of alder leaves in the mixture. Our results support the hypothesis of a consistent slowing down of the decomposition process as a result of plant biodiversity loss, and hence effects on stream ecosystem functioning, especially when a key (N-fixing) species is lost; and underscore the importance of detritivores as drivers of plant diversity effects in the studied ecosystem processes. This study was funded by the 2014–2020 FEDER Operative Program Andalusia (RIOVEGEST project, Ref. FEDER-UAL18 -RNM -B006 – B, to J.J.C). Additional support was provided by the Spanish Ministry for Science, Innovation and Universities and FEDER (BioLoss project, Ref. RTI2018-095023- B-I00, to L.B.). Rubio-Ríos was supported by an FPU grant of the Spanish Ministry of Education, Culture and Sports (reference FPU16/03734).

1. Many experiments have shown that biodiversity promotes ecosystem functioning and stability and that this relationship varies with resource availability. However, we still have a poor understanding of the underlying physiological and ecological mechanisms driving diversity effects and how they may interact with soil nutrient availability. 2. We collected data in a grassland experiment factorially manipulating fertilization, species richness (SR), functional composition (slow-growing vs. fast-growing species) and functional diversity in resource economic traits. We measured above-ground productivity (AP), nitrogen (N) uptake, photosynthesis and water use efficiency by combining a 15N labelling approach with productivity, gas exchange and stable isotope measurements in 3 years differing in rainfall. 3. We found that sown SR increased AP, N uptake and photosynthesis, suggesting that SR is the most important driver of ecosystem productivity and nutrient cycling. Similarly, photosynthesis was affected by functional composition but not by functional diversity. Water use efficiency was reduced by sown SR for communities dominated by slow-growing species but not for communities dominated by fast-growing species. Fertilization increased productivity, N uptake and water use efficiency. The positive effects of high SR on ecosystem functions were independent of fertility levels. 4. Synthesis. Our results provide evidence that high species richness in temperate grasslands could enhance productivity and reduce the negative impacts of drought events. Multiple factors and community characteristics are important in driving enhanced ecosystem functioning in biodiverse grasslands and seem to affect functioning and stability through different mechanisms. ISSN:0022-0477

Forest structural complexity has been identified as an important driver for promoting simultaneously biodiversity across trophic levels and multiple ecosystem services. However, we still have a limited understanding of the processes that lead to structural complex stands and how they evolve over time. Using terrestrial laser scanning (TLS), we quantified a three-dimensional (3D) stand structural complexity index (SSCI) in an experimental plantation with a long gradient of tree species richness (1–24 species). The plantation was established in 2009, and we made use of a multi-temporal TLS dataset recorded during 2012–2019. We found a positive relationship between tree species richness and structural complexity. This relationship became stronger over time. Ten years after planting, SSCI was on average two-fold higher in 16- and 24-species mixtures than in monocultures. Furthermore, we demonstrate that tree species richness promotes 3D stand structural complexity indirectly by fostering a high vertical heterogeneity and thus greater spatial complementarity in canopy space. Synthesis and applications. Our findings indicate that tree species richness plays a crucial role in promoting stand structural complexity in young plantations, and this role becomes more important already during early stand development. Thus, afforestation measures would benefit from planting multiple native tree species to initiate structurally complex stands.

International audience; Rising sea surface temperatures are expected to lead to the loss of phytoplankton biodiversity. However, we currently understand very little about the interactions between warming, loss of phy-toplankton diversity and its impact on the oceans' primary production. We experimentally manipulated the species richness of marine phytoplankton communities under a range of warming scenarios, and found that ecosystem production declined more abruptly with species loss in communities exposed to higher temperatures. Species contributing positively to ecosystem production in the warmed treatments were those that had the highest optimal temperatures for photosynthe-sis, implying that the synergistic impacts of warming and biodiversity loss on ecosystem functioning were mediated by thermal trait variability. As species were lost from the communities, the probability of taxa remaining that could tolerate warming diminished, resulting in abrupt declines in ecosystem production. Our results highlight the potential for synergistic effects of warming and biodiversity loss on marine primary production.

From the establishment of the first biodiversity experiments in the 1990s, studies have consistently reported positive relationships between plant diversity and productivity in grasslands. However, the predominant hypotheses that may explain this pattern have changed. Initially, there was a strong focus on plant–plant interactions such as facilitation and resource partitioning, but the results from the first experiments that manipulated soil communities have led to a paradigm shift. In the current view on mechanisms that drive plant diversity–productivity relationships, fungal pathogen-induced reductions of plant productivity at low diversity play an important role. This role rests on two assumptions: the effects of pathogens (a) are plant-species specific (i.e. not all plant species are affected equally by a fungal pathogen) and (b) display negative density dependence (i.e. decrease with decreasing host plant density and hence, with increasing plant species richness). Here, we review the empirical evidence for these two assumptions. In the biodiversity literature, this is mainly based on indirect approaches, such as soil sterilization, plant–soil feedback studies and plant biomass patterns. The identification and functional characterization of the fungal pathogens that actually drive the plant diversity–productivity relationship have only recently started. Synthesis. Nevertheless, these studies, together with studies on plant–pathogen interactions in agricultural crops and forests, clearly suggest host-specific, negative density-dependent effects of fungal pathogens are common. Moreover, recent studies suggest that the reduced impact of pathogens at high plant diversity depends not just on host density but also on effects of neighbouring (non-host) plant species on the pathogen. Understanding how neighbouring plants affect the interactions between a pathogen and its host plants and disentangling the role of plant–pathogen interactions from other mechanisms potentially driving diversity–productivity relationships are important future challenges.

Altres ajuts: Ramon Areces Foundation. Grant Number BEVP27P01A3355 Soil fauna play a fundamental role on key ecosystem functions like organic matter decomposition, although how local assemblages are responding to climate change and whether these changes may have consequences to ecosystem functioning is less clear. Previous studies have revealed that a continued environmental stress may result in poorer communities by filtering out the most sensitive species. However, these experiments have rarely been applied to climate change factors combining multiyear and multisite standardized field treatments across climatically contrasting regions, which has limited drawing general conclusions. Moreover, other facets of biodiversity, such as functional and phylogenetic diversity, potentially more closely linked to ecosystem functioning, have been largely neglected. Here, we report that the abundance, species richness, phylogenetic diversity, and functional richness of springtails (Subclass Collembola), a major group of fungivores and detritivores, decreased within 4 years of experimental drought across six European shrublands. The loss of phylogenetic and functional richness was higher than expected by the loss of species richness, leading to communities of phylogenetically similar species sharing evolutionary conserved traits. Additionally, despite the great climatic differences among study sites, we found that taxonomic, phylogenetic, and functional richness of springtail communities alone were able to explain up to 30% of the variation in annual decomposition rates. Altogether, our results suggest that the forecasted reductions in precipitation associated with climate change may erode springtail communities and likely other drought-sensitive soil invertebrates, thereby retarding litter decomposition and nutrient cycling in ecosystems

International audience; The 21st century has seen an acceleration of anthropogenic climate change and biodiversity loss, with both stressors deemed to affect ecosystem functioning. However, we know little about the interactive effects of both stressors and in particular about the interaction of increased climatic variability and biodiversity loss on ecosystem functioning. This should be remedied because larger climatic variability is one of the main features of climate change. Here, we demonstrated that temperature fluctuations led to changes in the importance of biodiversity for ecosystem functioning. We used microcosm communities of different phytoplankton species richness and exposed them to a constant, mild, and severe temperature-fluctuating environment. Wider temperature fluctuations led to steeper biodiversity–ecosystem functioning slopes, meaning that species loss had a stronger negative effect on ecosystem functioning in more fluctuating environments. For severe temperature fluctuations, the slope increased through time due to a decrease of the productivity of species-poor communities over time. We developed a theoretical competition model to better understand our experimental results and showed that larger differences in thermal tolerances across species led to steeper biodiversity–ecosystem functioning slopes. Species-rich communities maintained their ecosystem functioning with increased fluctuation as they contained species able to resist the thermally fluctuating environments, while this was on average not the case in species-poor communities. Our results highlight the importance of biodiversity for maintaining ecosystem functions and services in the context of increased climatic variability under climate change.

International audience; Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

Significance Food security is not simply about maintaining yields, but it is also about the need for a stable supply of nutritionally diverse foods. Obtaining nutritious food is a major challenge facing humanity, and diverse aquatic ecosystems can help meet this goal. To test how aquatic biodiversity affects human health, we assembled a dataset of nutrients, contaminants, and ecological traits of 801 aquatic species. We used ecological models to quantify the role of species richness and ecological functional diversity and found that these biodiversity dimensions enhanced seafood micronutrient and fatty acid provisioning by the same mechanisms that link biodiversity to productivity in grasslands, forests, and other systems. Our results underscore the need to minimize aquatic biodiversity loss to sustain and improve human well-being., Humanity depends on biodiversity for health, well-being, and a stable environment. As biodiversity change accelerates, we are still discovering the full range of consequences for human health and well-being. Here, we test the hypothesis—derived from biodiversity–ecosystem functioning theory—that species richness and ecological functional diversity allow seafood diets to fulfill multiple nutritional requirements, a condition necessary for human health. We analyzed a newly synthesized dataset of 7,245 observations of nutrient and contaminant concentrations in 801 aquatic animal taxa and found that species with different ecological traits have distinct and complementary micronutrient profiles but little difference in protein content. The same complementarity mechanisms that generate positive biodiversity effects on ecosystem functioning in terrestrial ecosystems also operate in seafood assemblages, allowing more diverse diets to yield increased nutritional benefits independent of total biomass consumed. Notably, nutritional metrics that capture multiple micronutrients and fatty acids essential for human well-being depend more strongly on biodiversity than common ecological measures of function such as productivity, typically reported for grasslands and forests. Furthermore, we found that increasing species richness did not increase the amount of protein in seafood diets and also increased concentrations of toxic metal contaminants in the diet. Seafood-derived micronutrients and fatty acids are important for human health and are a pillar of global food and nutrition security. By drawing upon biodiversity–ecosystem functioning theory, we demonstrate that ecological concepts of biodiversity can deepen our understanding of nature’s benefits to people and unite sustainability goals for biodiversity and human well-being.

Plant diversity begets diversity at other trophic levels. While species richness is the most commonly used measure for plant diversity, the number of evolutionary lineages (i.e. phylogenetic diversity) could theoretically have a stronger influence on the community structure of co-occurring organisms. However, this prediction has only rarely been tested in complex real-world ecosystems. Using a comprehensive multitrophic dataset of arthropods and fungi from a species-rich subtropical forest, we tested whether tree species richness or tree phylogenetic diversity relates to the diversity and composition of organisms. We show that tree phylogenetic diversity but not tree species richness determines arthropod and fungi community composition across trophic levels and increases the diversity of predatory arthropods but decreases herbivorous arthropod diversity. The effect of tree phylogenetic diversity was not mediated by changed abundances of associated organisms, indicating that evolutionarily more diverse plant communities increase niche opportunities (resource diversity) but not necessarily niche amplitudes (resource amount). Our findings suggest that plant evolutionary relatedness structures multitrophic communities in the studied species-rich forests and possibly other ecosystems at large. As global change non-randomly threatens phylogenetically distinct plant species, far-reaching consequences on associated communities are expected. A free Plain Language Summary can be found within the Supporting Information of this article.

The relationship between biodiversity and ecosystem functioning (BEF) is a central issue in soil and microbial ecology. To date, most belowground BEF studies focus on the diversity of microbes analyzed by barcoding on total DNA, which targets both active and inactive microbes. This approach creates a bias as it mixes the part of the microbiome currently steering processes that provide actual ecosystem functions with the part not directly involved. Using experimental extensive grasslands under current and future climate, we used the bromodeoxyuridine (BrdU) immunocapture technique combined with pair-end Illumina sequencing to characterize both total and active microbiomes (including both bacteria and fungi) in the rhizosphere of Trifolium pratense. Rhizosphere function was assessed by measuring the activity of three microbial extracellular enzymes (β-glucosidase, N-acetyl-glucosaminidase, and acid phosphatase), which play central roles in the C, N, and P acquisition. We showed that the richness of overall and specific functional groups of active microbes in rhizosphere soil significantly correlated with the measured enzyme activities, while total microbial richness did not. Active microbes of the rhizosphere represented 42.8 and 32.1% of the total bacterial and fungal taxa, respectively, and were taxonomically and functionally diverse. Nitrogen fixing bacteria were highly active in this system with 71% of the total operational taxonomic units (OTUs) assigned to this group detected as active. We found the total and active microbiomes to display different responses to variations in soil physicochemical factors in the grassland, but with some degree of resistance to a manipulation mimicking future climate. Our findings provide critical insights into the role of active microbes in defining soil ecosystem functions in a grassland ecosystem. We demonstrate that the relationship between biodiversity-ecosystem functioning in soil may be stronger than previously thought.

International audience; Biomass production in ecosystems is a complex process regulated by several facets of biodiversity and species identity, but also species interactions such as competition or complementarity between species. For studying these different facets separately, ecosystem biomass is generally partitioned in two biodiversity effects. The composition effect is a simple, linear effect, and the interaction effect is a more subtle, nonlinear effect. Here we used a clustering approach (1) to separately and comprehensively capture all linear and nonlinear effects induced by both biodiversity effects on ecosystem functioning, and (2) to determine the functional composition at the origin of each biodiversity effect. We used data from the long-term Cedar Creek BioDIV experiment carried out over 22 yr, and we partitioned multiplicatively the biomass in composition and interaction effects. Both biodiversity effects were weakly correlated. Our clustering approach accurately explains and predicts each diversity effect over time: each one is modeled by a different functional composition. Even if environmental conditions and the strength of interaction effect strongly varied over time, the functional clusters of species that govern the interaction effect do not change over the 22 yr of the experiment. The functional composition governing the interaction effect is therefore very robust. In contrast, the functional clusters of species that govern the composition effect are less robust and change with environmental conditions. Understanding ecosystem functioning therefore requires that ecological properties are first partitioned by type, then each type of property is analyzed and modeled separately. Approaches without a priori groupings of species, such as functional clustering, appear particularly efficient and robust to unravel the web of species interactions, and identify the role played by species on biodiversity effects.

Predicting the impacts of global change on highly dynamic ecosystems requires a better understanding of how communities respond to disturbance duration, frequency and timing. Intermittent rivers and ephemeral streams are dynamic ecosystems that are recognized as the most common fluvial ecosystem globally. The complexity of the drying process can give rise to different annual and antecedent hydrological conditions, but their effect on aquatic communities remains unclear. Here, using aquatic invertebrates from 33 streams across a flow-intermittence gradient, we assessed how annual (drying duration and frequency) and recent drying characteristics (duration of the last dry period and flowing duration since the last rewetting) affect the density and diversity metrics of communities and trophic groups while controlling for other key abiotic factors (dissolved oxygen and altitude). We characterized invertebrate communities using taxonomy and functional traits to capture biological features that increase vulnerability to drying. In addition, using structural equation modelling (SEM), we evaluated pathways by which drying characteristics directly impact invertebrate density and whether diversity indirectly mediates such relationships. We show that drying frequency drove reductions in diversity at the community level and within trophic groups, whereas both the drying duration and frequency had a negative influence on density metrics. Reductions in taxonomic richness were linked to increased annual drying duration, whereas functional diversity declined in response to annual drying frequency. Filterer, predator and shredder trophic groups exhibited the strongest negative responses to drying. Recent drying characteristics had a minor effect on density and diversity metrics. Our SEM results demonstrated that diversity mediates the negative impacts of annual drying duration and frequency on invertebrate density through reductions in their taxonomic richness and functional diversity. Our results underscore the importance of considering multiple drying characteristics together with the interdependence of density and diversity to better anticipate drying responses in freshwater ecosystems. Keywords: biodiversity-ecosystem functioning, drying, flow intermittence, functional traits, intermittent rivers and ephemeral streams, Mediterranean streams

Plant–soil feedback (PSF) and diversity–productivity relationships are important research fields to study drivers and consequences of changes in plant biodiversity. While studies suggest that positive plant diversity–productivity relationships can be explained by variation in PSF in diverse plant communities, key questions on their temporal relationships remain. Here, we discuss three processes that change PSF over time in diverse plant communities, and their effects on temporal dynamics of diversity–productivity relationships: spatial redistribution and changes in dominance of plant species; phenotypic shifts in plant traits; and dilution of soil pathogens and increase in soil mutualists. Disentangling these processes in plant diversity experiments will yield new insights into how plant diversity– productivity relationships change over time. published

International audience; Tree diversity has been shown to promote a broad range of ecosystem functions in forests. However, how important these effects are in driving ecosystem multifunctionality in natural forests, relative to other drivers, such as below‐ground biodiversity (e.g. soil microbial diversity), community‐level functional traits and environmental conditions, remains poorly understood. Here, we hypothesize that tree species or phylogenetic diversity (PD), stand structure, functional traits and soil microbial diversity jointly regulate temperate forest multifunctionality (FM) along a local‐scale environmental gradient.Using repeated census data from a 25‐ha old‐growth temperate forest, we first quantified eight ecosystem functions and properties related to above‐ and below‐ground nutrient cycling. We then used these to estimate ecosystem multifunctionality using both averaging and multiple threshold (50%, 75% and 95%) approaches. Finally, we used structural equation models to explore how different facets of tree (tree species, functional and PD) and soil (bacteria, fungi and nematode diversity) biodiversity influence ecosystem multifunctionality, as well as how these relationships are modulated by stand structural attributes and environmental conditions (topography and soil nutrients). Forest multifunctionality was positively related to stand structural complexity but negatively related to acquisitive traits (i.e. community‐weighted mean of specific leaf area). Plant PD had no significant direct effect on FM, but it had a significant indirect effect via increased stand structural complexity. The effect of soil microbial diversity on FM increased with increasing threshold levels of FM and outperformed tree diversity and environmental conditions at the highest threshold level (i.e. 95%). Forests on steep slopes had lower levels of ecosystem multifunctionality due to decreased stand structural complexity. Soil nutrients were responsible for regulating FM via plant trait composition and, to a lesser extent, via tree diversity, stand structure and soil microbial diversity.Synthesis . Plant PD, stand structure and soil microbial diversity jointly regulated FM, and these effects were influenced by local‐scale changes in environmental conditions. Soil microbial diversity was a key driver of highly multifunctional forests, whereas conservation of complex stand structure and conservative trait dominance could enhance mean values of multiple functions.

The ongoing loss of biodiversity and global environmental changes severely affect the structure of coastal ecosystems. Consequences, in terms of ecosystem functioning, are, however, difficult to predict because the context dependency of the biodiversity-ecosystem function relationships within these heterogeneous seascapes is poorly understood. To assess the effects of biological and environmental factors in mediating ecosystem functioning (nutrient cycling) in different natural habitats, intact sediment cores were collected at 18 sites on a grain size gradient from coarse sand to silt, with varying organic matter content and vegetation. To assess ecosystem functioning, solute fluxes (O-2, NH4+, PO43-, Si) across the sediment-water interface were measured. The macrofaunal communities changed along the grain size gradient with higher abundance, biomass and number of species in coarser sediments and in habitats with more vegetation. Across the whole gradient, the macrofauna cumulatively accounted for 25% of the variability in the multivariate solute fluxes, whereas environmental variables cumulatively accounted for 20%. Only the biomass and abundance of a few of the most dominant macrofauna species, not the number of species, appeared to contribute significantly to the nutrient recycling processes. Closer analyses of different sediment types (grouped into coarse, medium and fine sediment) showed that the macrofauna was an important predictor in all sediment types, but had the largest impact in fine and medium sediments. The results imply that even if the ecosystem functioning is similar in different sediment types, the underpinning mechanisms are different, which makes it challenging to generalize patterns of functioning across the heterogeneous shallow coastal zones.

1.There is growing interest in predicting how loss of species diversity and abundance affect the structure and functioning of ecosystems. Tadpole diversity and abundance can be exceptionally high in tropical streams, but, compared to other groups, relatively little is known about their functional roles. We assessed the trophic niches and investigated the contribution of tadpoles to nutrient recycling (excretion and egestion) and litter breakdown in streams. 2.We used two ecomorphologically distinct tadpoles belonging to the two most dominant feeding guilds in Ranomafana, Madagascar: Boophis quasiboehmei (hereafter BQ, generalised mouthpart, grazer) and Mantidactylus melanopleura (hereafter MM, umbelliform funnel mouthpart, suspension feeder). We conducted field incubation experiments to quantify nutrients recycled from excretion and egestion, and set enclosures to analyse the effects of tadpoles on litter breakdown (leaves of Pauridiantha sp. and Chrysophyllum sp.) in nine treatments: control (no tadpoles), monospecific treatment (BQ or MM) at three densities (low, medium, high: 3, 6, 12 tadpoles/0.0625 m2, respectively) and mix‐species treatment (3 BQ + 3 MM, 6 BQ + 6 MM). 3.BQ and MM occupied the same trophic level but tended to differ in their carbon isotopic signatures. MM excreted nitrogen (N) and phosphorus (P) at higher rates, but the two species had similar N:P molar excretion ratio. Nutrients recycled from faecal pellets (egestion) were not immediately available but needed to be mineralised: N increased with time in the water column and was more than 25 times higher in concentration at the end of the experiment (day 16), whereas P concentration showed a hump‐shaped pattern with a maximum value at day 4 of incubation. Effects of tadpoles on litter breakdown depended on tadpole identity, density and litter identity. Particularly, no breakdown occurred at low tadpole density, and effects were generally stronger on the softer texture leaves Pauridiantha sp. We found additive effects of tadpole diversity on litter breakdown. 4.These findings indicate that (1) tadpoles with different mouthparts play different roles on the ecosystem; (2) tadpole faecal pellets are important latent sources of nutrients in freshwater environments; and (3) tadpole abundance exerted stronger effects than species diversity on litter breakdown, emphasising the importance of tadpole biomass and communities in tropical streams. Interspecific variation in nutrient recycling and differential effects on litter breakdown illustrate a strong linkage between species identity and ecosystem function., ファイル公開：2019-02-01

This research was funded by the EU Seventh Framework Programme for research, technological development and demonstration (FP7/2007-2013) within the Ocean of Tomorrow call under Grant Agreement No.266445 for the project Vectors of Change in Oceans and Seas Marine Life (VECTORS). AMQ and PJS acknowledge support from the UK Natural Environment Research Council and Department for Environment, Food and Rural Affairs [grant number NE/L003279/1, Marine Ecosystems Research Programme]. HO and JK were partly funded by the Estonian Ministry of Education and Research (grant SF0180005s10) and the Estonian Research Council (IUT02-20). Invasive ecosystem engineers (IEE) are potentially one of the most influential types of biological invaders. They are expected to have extensive ecological impacts by altering the physical-chemical structure of ecosystems, thereby changing the rules of existence for a broad range of resident biota. To test the generality of this expectation, we used a global systematic review and meta-analysis to examine IEE effects on the abundance of individual species and communities, biodiversity (using several indices) and ecosystem functions, focusing on marine and estuarine environments. We found that IEE had a significant effect (positive and negative) in most studies testing impacts on individual species, but the overall (cumulative) effect size was small and negative. Many individual studies showed strong IEE effects on community abundance and diversity, but the direction of effects was variable, leading to statistically non-significant overall effects in most categories. In contrast, there was a strong overall effect on most ecosystem functions we examined. IEE negatively affected metabolic functions and primary production, but positively affected nutrient flux, sedimentation and decomposition. We use the results to develop a conceptual model by highlighting pathways whereby IEE impact communities and ecosystem functions, and identify several sources of research bias in the IEE-related invasion literature. Only a few of the studies simultaneously quantified IEE effects on community/diversity and ecosystem functions. Therefore, understanding how IEE may alter biodiversity-function relationships should be a primary focus of future studies of invasion biology. Moreover, the clear effects of IEE on ecosystem functions detected in our study suggest that scientists and environmental managers ought to examine how the effects of IEE might be manifested in the services that marine ecosystems provide to humans. Postprint

Tropical forests store and sequester large amounts of carbon in above- and below-ground plant biomass and soil organic matter (SOM), but how these are driven by abiotic and biotic factors remains poorly understood. Here, we test the effects of abiotic factors (light variation, caused by logging disturbance, and soil fertility) and biotic factors (species richness and functional trait composition) on biomass stocks (above-ground biomass, fine root biomass), SOM and productivity in a relatively monodominant Guyanese tropical rainforest. This forest grows on nutrient-poor soils and has few species that contribute most to total abundance. We, therefore, expected strong effects of soil fertility and species’ traits that determine resource acquisition and conservation, but not of diversity. We evaluated 6 years of data for 30 0.4-ha plots and tested hypotheses using structural equation models. Disturbance increased productivity but decreased above-ground biomass stocks. Soil phosphorus (P) enhanced above-ground biomass and productivity, whereas soil nitrogen reduced fine root biomass. In contrast to expectations, trait values representing acquisitive strategies (e.g. high leaf nutrient concentration) increased biomass stocks, possibly because they indicate higher nutrient absorption and thus higher biomass build-up. However, under harsh conditions where biomass increase is slow, acquisitive trait values may increase respiration and vulnerability to hazards and therefore increase biomass loss. As expected, species richness did not affect productivity. We conclude that light availability (through disturbance) and soil fertility—especially P—strongly limit forest biomass productivity and stocks in this Guyanese forest. Low P availability may cause strong environmental filtering, which in turn results in a small set of dominant species. As a result, community trait composition but not species richness determines productivity and stocks of biomass and SOM in tropical forest on poor soils. A plain language summary is available for this article.