Biodiversity-ecosystem Functioning Research Research Articles

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses.

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Diversity–functioning relationships across hierarchies of biological organization

Numerous biodiversity–ecosystem functioning (BEF) experiments have shown that plant community productivity typically increases with species diversity. In these studies, diversity is generally quantified using metrics of taxonomic, phylogenetic, or functional differences among community members. Research has also shown that the relationships between species diversity and functioning depends on the spatial scale considered, primarily because larger areas may contain different ecosystem types and span gradients in environmental conditions, which result in a turnover of the species set present locally. A fact that has received little attention, however, is that ecological systems are hierarchically structured, from genes to individuals to communities to entire landscapes, and that additional biological variation occurs at levels of organization above and below those typically considered in BEF research. Here, we present cases of diversity effects at different hierarchical levels of organization and compare these to the species‐diversity effects traditionally studied. We argue that when this evidence is combined across levels, a general framework emerges that allows the transfer of insights and concepts between traditionally disparate disciplines. Such a framework presents an important step towards a better understanding of the functional importance of diversity in complex, real‐world systems.

Enhancing the structural diversity between forest patches-A concept and real-world experiment to study biodiversity, multifunctionality and forest resilience across spatial scales.

Intensification of land use by humans has led to a homogenization of landscapes and decreasing resilience of ecosystems globally due to a loss of biodiversity, including the majority of forests. Biodiversity-ecosystem functioning (BEF) research has provided compelling evidence for a positive effect of biodiversity on ecosystem functions and services at the local (α-diversity) scale, but we largely lack empirical evidence on how the loss of between-patch β-diversity affects biodiversity and multifunctionality at the landscape scale (γ-diversity). Here, we present a novel concept and experimental framework for elucidating BEF patterns at α-, β-, and γ-scales in real landscapes at a forest management-relevant scale. We examine this framework using 22 temperate broadleaf production forests, dominated by Fagus sylvatica. In 11 of these forests, we manipulated the structure between forest patches by increasing variation in canopy cover and deadwood. We hypothesized that an increase in landscape heterogeneity would enhance the β-diversity of different trophic levels, as well as the β-functionality of various ecosystem functions. We will develop a new statistical framework for BEF studies extending across scales and incorporating biodiversity measures from taxonomic to functional to phylogenetic diversity using Hill numbers. We will further expand the Hill number concept to multifunctionality allowing the decomposition of γ-multifunctionality into α- and β-components. Combining this analytic framework with our experimental data will allow us to test how an increase in between patch heterogeneity affects biodiversity and multifunctionality across spatial scales and trophic levels to help inform and improve forest resilience under climate change. Such an integrative concept for biodiversity and functionality, including spatial scales and multiple aspects of diversity and multifunctionality as well as physical and environmental structure in forests, will go far beyond the current widely applied approach in forestry to increase resilience of future forests through the manipulation of tree species composition.

The FraDiv experiment: Biodiversity-ecosystem functioning research meets reforestation practice

European ash-rich forest ecosystems are transforming rapidly under the influence of ash dieback, putting many associated species at risk. Forest managers face the urgent challenge to deal with the loss of European ash (Fraxinus excelsior L.) as a key tree species to maintain species richness and ecosystem functioning. The project FraDivexp, located in Schleswig-Holstein, Germany, aims at counteracting detrimental effects of progressive ash decline by testing alternative tree species in a Biodiversity-Ecosystem Functioning (BEF) experiment along a hydrological gradient. Here, we provide insight into how a BEF-approach can be combined with silvicultural management practice to meet the needs for both ecological research and reforestation. At the same time, we present first data on the survival of the planted saplings.In winter 2019/2020, FraDivexp was established with autochthonous tree species considered potential substitutes for the functioning of ash. At 12 sites, plantations including Fraxinus excelsior, Acer platanoides L., Carpinus betulus L., Tilia cordata Mill. and Ulmus laevis Pall. were planted directly underneath the remains of collapsing forest canopies involving all monocultures, and all combinations of 2-, 4- and 5-species mixtures. One year after planting of 25,200 trees, total mortality was at 5% with U. laevis showing lowest mortality while establishment of A.platanoides was least successful. In this early phase of FraDivexp tree mortality was species-specific and driven by initial individual tree size, pH-values in the topsoil and canopy openness, while there was no effect associated with tree diversity. Analysis of further biotic factors showed high mortality of A.platanoides in areas with a high cover of Rubus spp. in the herb layer, indicating species-specific susceptibility to different site conditions. Overall, low mortality (compared to other BEF experiments on arable land) suggests an advantage of establishing a BEF experiment within an existing forest matrix. Simultaneously, this study shows that differences in environmental context dependency among species need to be considered more explicitly, when recommending management strategies. To ensure successful establishment of reforestations with substitute tree species is the first step to efficiently counteract the massive loss of ash trees with the aim of maintaining biodiversity and ecosystem functioning.

Why are biodiversity-ecosystem functioning relationships so elusive? Trophic interactions may amplify ecosystem function variability.

The relationship between biodiversity and ecosystem functions (BEFs) has attracted great interest. Studies on BEF have so far focused on the average trend of ecosystem function as species diversity increases. A tantalizing but rarely addressed question is why large variations in ecosystem functions are often observed across systems with similar species diversity, likely obscuring observed BEFs. Here we use a multi-trophic food web model in combination with empirical data to examine the relationships between species richness and the variation in ecosystem functions (VEFs) including biomass, metabolism, decomposition, and primary and secondary production. We then probe the mechanisms underlying these relationships, focusing on the role of trophic interactions. While our results reinforce the previously documented positive BEF relationships, we found that ecosystem functions exhibit significant variation within each level of species richness and the magnitude of this variation displays a hump-shaped relationship with species richness. Our analyses demonstrate that VEFs is reduced when consumer diversity increases through elevated nonlinearity in trophic interactions, and/or when the diversity of basal species such as producers and decomposers decreases. This explanation is supported by a 34-year empirical food web time series from the Gulf of Riga ecosystem. Our work suggests that biodiversity loss may not only result in ecosystem function decline, but also reduce the predictability of functions by generating greater function variability among ecosystems. It thus helps to reconcile the debate on the generality of positive BEF relationships and to disentangle the drivers of ecosystem stability. The role of trophic interactions and the variation in their strengths mediated by functional responses in shaping ecosystem function variation warrants further investigations and better incorporation into biodiversity-ecosystem functioning research.

We should not necessarily expect positive relationships between biodiversity and ecosystem functioning in observational field data.

Our current, empirical understanding of the relationship between biodiversity and ecosystem function is based on two information sources. First, controlled experiments which show generally positive relationships. Second, observational field data which show variable relationships. This latter source coupled with a lack of observed declines in local biodiversity has led to the argument that biodiversity-ecosystem functioning relationships may be uninformative for conservation and management. We review ecological theory and re-analyse several biodiversity datasets to argue that ecosystem function correlations with local diversity in observational field data are often difficult to interpret in the context of biodiversity-ecosystem function research. This occurs because biotic interactions filter species during community assembly which means that there can be a high biodiversity effect on functioning even with low observed local diversity. Our review indicates that we should not necessarily expect any specific relationship between local biodiversity and ecosystem function in observational field data. Rather, linking predictions from biodiversity-ecosystem function theory and experiments to observational field data requires considering the pool of species available during colonisation: the local species pool. We suggest that, even without local biodiversity declines, biodiversity loss at regional scales-which determines local species pools-may still negatively affect ecosystem functioning.

Biodiversity and ecosystem functioning: Have our experiments and indices been underestimating the role of facilitation?

Abstract After 25 years of biodiversity experiments, it is clear that higher biodiversity (B) plant communities are usually more productive and often have greater ecosystem functioning (EF) than lower diversity communities. However, the mechanisms underlying this positive biodiversity–ecosystem functioning (BEF) relationship are still poorly understood. The vast majority of past work in BEF research has focused on the roles of mathematically partitioned complementarity and selection effects. While these mathematical approaches have provided insights into underlying mechanisms, they have focused strongly on competition and resource partitioning. Importantly, mathematically partitioned complementarity effects include multiple facilitative mechanisms, including dilution of species‐specific pathogens, positive changes in soil nutrient cycling, associational defence and microclimate amelioration. Synthesis. This Special Feature takes an experimental and mechanistic approach to teasing out the facilitative mechanisms that underlie positive BEF relationships. As an example, we demonstrate diversity‐driven changes in microclimate amelioration. Articles in this Special Feature explore photoinhibition, experimental manipulations of microclimate, lidar examinations of plant canopy effects and higher‐order trophic interactions as facilitative mechanisms behind classic BEF processes. We emphasize the need for future BEF experiments to disentangle the facilitative mechanisms that are interlinked with niche complementarity to better understand the fundamental processes by which diversity regulates life on Earth.

Nonrandom species loss in phytoplankton communities and its effect on ecosystem functioning

AbstractThe effects of species diversity on ecosystem functioning have been broadly studied, mostly considering random artificial assemblages. However, natural communities are shaped by ecological interactions and environmental conditions often leading to nonrandom species extinctions. Here, we manipulated a natural phytoplankton community by generating a taxonomic diversity gradient based on rare species exclusions and conducted a mesocosm experiment to investigate the diversity effects on ecosystem functioning (resource use efficiency and biomass) under two nutrient levels. We quantified two functional traits (size and photosynthetic pigments) to evaluate the relation of functional diversity and ecosystem functioning. In a second experimental phase we simulated temperature fluctuations to assess the role of diversity on temporal stability of ecosystem functioning. We did not find a significant effect of diversity on ecosystem functioning and the temporal stability of ecosystem functioning, regardless of nutrient level. These results indicated that loss of biomass caused by rare species extinctions was compensated by the species retained in the diversity gradient. Phytoplankton size diversity was positively related to diversity, but this was not transferred into a positive diversity effect on ecosystem functioning. Additionally, the loss of species did not result in a loss of pigment diversity. The lack of a biodiversity–ecosystem functioning (BEF) relationship in our study may be due to the weak coupling of functional and species diversity and a low manifestation of functional diversity under the evaluated conditions. We emphasize that more realistic biodiversity loss scenarios in experiments can yield different results from those in classical BEF research paradigms.

Towards a multidimensional view of biodiversity and ecosystem functioning in a changing world

Towards a multidimensional view of biodiversity and ecosystem functioning in a changing world

Rhizobacterial species richness improves sorghum growth and soil nutrient synergism in a nutrient-poor greenhouse soil

Although microbes influence plant growth, little is known about the impact of microbial diversity on plant fitness trade-offs, intraspecific-interactions, and soil nutrient dynamics in the context of biodiversity-ecosystem functioning (BEF) research. The BEF theory states that higher species richness can enhance ecosystem functioning. Thus, we hypothesize that rhizobacterial species richness will alter sorghum (Sorghum bicolor L.) growth, soil nutrient dynamics and interactions (antagonism or synergism) in a nutrient-poor greenhouse soil. Using six rhizobacterial species in a BEF experiment, we tested the impact of a species richness gradient (0, 1, 3, 5 or 6 species per community) on plant growth, nutrient assimilation, and soil nutrient dynamics via seed-inoculation. Our experiment included, one un-inoculated control, six rhizobacterial monoculture (Pseudomonas poae, Pseudomonas sp., Bacillus pumilus., Pantoea agglomerance., Microbacterium sp., and Serratia marcescens), and their nine mixture treatments in triplicate (48). Rhizobacterial species richness enhanced per pot above- or below-ground dry mass. However, the per plant growth and plant nutrient assimilation declined, most likely, due to microbial-driven competitive interactions among sorghum plants. But nevertheless, some rhizobacterial monoculture and mixture treatments improved per plant (shoot and root) growth and nutrient assimilation as well. Soil nutrient contents were mostly lower at higher plant-associated rhizobacterial diversity; among these, the soil Zn contents decreased significantly across the rhizobacterial diversity gradient. Rhizobacterial diversity promoted synergistic interactions among soil nutrients and improved root–soil interactions. Overall, our results suggest that a higher rhizobacterial diversity may enhance soil–plant interactions and total productivity under resource limited conditions.

The species composition-ecosystem function relationship: A global meta-analysis using data from intact and recovering ecosystems.

The idea that biodiversity is necessary in order for ecosystems to function properly has long been used as a basic argument for the conservation of species, and has led to an abundance of research exploring the relationships between species richness and ecosystem function. Here we present a meta-analysis of global ecosystems using the Bray-Curtis index to explore more complex changes in the species composition of natural ecosystems, and their relationship with ecosystem functions. By using data recorded, firstly in reference sites and secondly in recovering sites, captured in restoration ecology studies, we pose the following questions: Firstly, how much variation is there in species composition and in ecosystem function in an intact ecosystem? Secondly, once an ecosystem has become degraded, is there a general relationship between its recovery in species composition and its recovery in ecosystem function? Thirdly, is this relationship the same for all types of ecosystem functions? Data from 21 studies yielded 478 comparisons of mean values for ecosystems. On Average, sites within the same intact natural ecosystems shared only a 48% similarity in species composition but were 69% similar in ecosystem functioning. In recovering ecosystems the relationship between species composition and ecosystem function was weak and saturating (directly accounting for only 2% of the variation). Only two of the six types of ecosystem function examined, biomass and biotic structure, showed a significant relationship with species composition, and the three types that measured soil functions showed no significant relationship. To date, most biodiversity-ecosystem function (BEF) research has been conducted in simplified ecosystems using the simple species richness metric. This study encourages a broader examination of the drivers of ecosystem functions under realistic scenarios of biodiversity change, and highlights the need to properly account for the extensive natural variation.

Local and landscape-level diversity effects on forest functioning.

Research of the past decades has shown that biodiversity is a fundamental driver of ecosystem functioning. However, most of this biodiversity-ecosystem functioning (BEF) research focused on experimental communities on small areas where environmental context was held constant. Whether the established BEF relationships also apply to natural or managed ecosystems that are embedded in variable landscape contexts remains unclear. In this study, we therefore investigated biodiversity effects on ecosystem functions in 36 forest stands that were located across a vast range of environmental conditions in managed landscapes of Central Europe (Switzerland). Specifically, we approximated forest productivity by leaf area index and forest phenology by growing-season length and tested effects of tree species richness and land-cover richness on these variables. We then examined the correlation and the confounding of these local and landscape-level diversity effects with environmental context variables related to forest stand structure (number of trees), landscape structure (land-cover edge density), climate (annual precipitation) and topography (mean altitude). We found that of all tested variables tree species richness was among the most important determinants of forest leaf area index and growing-season length. The positive effects of tree species richness on these two ecosystem variables were remarkably consistent across the different environmental conditions we investigated and we found little evidence of a context-dependent change in these biodiversity effects. Land-cover richness was not directly related to local forest functions but could nevertheless play a role via a positive effect on tree species richness.

Do biodiversity-ecosystem functioning experiments inform stakeholders how to simultaneously conserve biodiversity and increase ecosystem service provisioning in grasslands?

Two key stakeholders primarily important for nature conservation are farmers (and their lobby groups) and conservationists. Both have substantial inputs into environmental strategies and policies calling for biodiversity conservation aimed to directly increase ecosystem services. The scientific literature concurs that as biological diversity increases so do ecosystem functions and services in grasslands. While the evidence for this is strong, the majority comes from controlled small-scale biodiversity-ecosystem functioning (BEF) experiments. Thus, it is unclear whether the scientific basis for implementing BEF relationships into practice is sufficiently evidenced. Here we explore the applicability of findings from BEF experiments to the conservation and management of temperate grassland, a widespread and potentially highly biodiverse habitat. While we acknowledge that BEF research can reveal insights into fundamental mechanisms, the saturation of biodiversity effects at low levels and unrealistic (management) treatments widely impede the applicability of these experimental results to permanent grasslands. Additionally, the integration of BEF research results into practice is considerably hampered by experimental studies not answering stakeholders' crucial questions, e.g. is there evidence of biodiversity conservation potentials? Thus, stakeholders do not have a strong evidence base for taking decisions for the addressed management goals, except intensive production in (species-poor) temporary grasslands. If BEF work is to inform stakeholders future research needs to overcome unrealistic management, missing stakeholder involvement and ineffective communication. A new generation of applied BEF experiments employing applied, multi-actor approaches is needed to facilitate the relevance of BEF research for nature conservation, agriculture and land management.

Microbial diversity-ecosystem function relationships across environmental gradients

In light of increasing anthropogenic pressures on ecosystems around the globe, the question how biodiversity change of organisms in the critical zone between Earth’s canopies and bedrock relates to ecosystem functions is an urgent issue, as human life relies on these functions. Particularly, soils play vital roles in nutrient cycling, promotion of plant growth, water purification, litter decomposition, and carbon storage, thereby securing food and water resources and stabilizing the climate. Soil functions are carried to a large part by complex communities of microorganisms, such as bacteria, archaea, fungi and protists. The assessment of microbial diversity and the microbiome's functional potential continues to pose significant challenges. Next generation sequencing offers some of the most promising tools to help shedding light on microbial diversity-function relationships. Studies relating microbial diversity and ecosystem functions are rare, particularly those on how this relationship is influenced by environmental gradients. The proposed project focuses on decomposition as one of the most important microbial soil ecosystem functions. The researchers from the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig combine an unparalleled range of expertise from next generation sequencing- based analysis of microbial communities (“meta-omics”) to soil ecology and biodiversity-ecosystem function research. This consortium will make use of soil samples from large international networks to assess microbial diversity both at the taxonomic and functional level and across the domains of life. By linking microbial diversity to functional measurements of decomposition and environmental gradients, the proposed project aims to achieve a comprehensive scale-independent understanding of environmental drivers and anthropogenic effects on the structural and functional diversity of microbial communities and subsequent consequences for ecosystem functioning.

Linking microbial communities to ecosystem functions: what we can learn from genotype-phenotype mapping in organisms.

Microbial physiological processes are intimately involved in nutrient cycling. However, it remains unclear to what extent microbial diversity or community composition is important for determining the rates of ecosystem-scale functions. There are many examples of positive correlations between microbial diversity and ecosystem function, but how microbial communities 'map' onto ecosystem functions remain unresolved. This uncertainty limits our ability to predict and manage crucial microbially mediated processes such as nutrient losses and greenhouse gas emissions. To overcome this challenge, we propose integrating traditional biodiversity-ecosystem function research with ideas from genotype-phenotype mapping in organisms. We identify two insights from genotype-phenotype mapping that could be useful for microbial biodiversity-ecosystem function studies: the concept of searching 'agnostically' for markers of ecosystem function and controlling for population stratification to identify microorganisms uniquely associated with ecosystem function. We illustrate the potential for these approaches to elucidate microbial biodiversity-ecosystem function relationships by analysing a subset of published data measuring methane oxidation rates from tropical soils. We assert that combining the approaches of traditional biodiversity-ecosystem function research with ideas from genotype-phenotype mapping will generate novel hypotheses about how complex microbial communities drive ecosystem function and help scientists predict and manage changes to ecosystem functions resulting from human activities. This article is part of the theme issue 'Conceptual challenges in microbial community ecology'.

Coarse root architecture: Neighbourhood and abiotic environmental effects on five tropical tree species growing in mixtures and monocultures

Most biodiversity-ecosystem function research focusses above-ground; if it considers roots, it considers fine roots, while coarse roots remain a “black box”. We utilized the Sardinilla experiment in Panamá, the oldest tropical tree diversity experiment, to test how species mixtures at the plot and neighbourhood scales and abiotic environmental characteristics affected 7 coarse root traits of 5 tropical tree species. Sardinilla was planted in 2001 with a gradient of native tree species richness of two-, three- and five-species mixtures and their respective monocultures. Root systems of 128 mature trees were excavated 0.5 m radially and one coarse root was fully excavated; unexcavated root lengths were predicted using species-specific allometric relationships. Root traits included the observed traits primary root length, diameter, and number, the number of secondary roots per meter of primary root, predicted root system extent and total predicted length of roots, and coarse root biomass. Tree size scaled positively with most root traits. Species identity (conspecific or heterospecific) and size of near neighbours were found to explain more variation (63.0%) in root traits than abiotic environmental characteristics (30.4%). Trees in waterlogged plots grew fewer, longer roots. Trees reduced root system extent but grew more roots when growing with conspecifics or growing in plots of high soil nitrogen and greater depth to water table. These findings suggest strategies employed by tropical tree species to both reduce competition with neighbours and make the most of local abiotic conditions, bringing us closer to understanding the role of coarse roots in the context of BEF research in forests.

Biomass allocation and productivity-richness relationship across four grassland types at the Qinghai Plateau.

Aboveground biomass (AGB) and belowground biomass (BGB) allocation and productivity–richness relationship are controversial. Here, we assessed AGB and BGB allocation and the productivity–richness relationship at community level across four grassland types based on the biomass data collected from 80 sites across the Qinghai Plateau during 2011–2012. The reduced major axis regression and general linear models were used and showed that (a) the median values of AGB were significantly higher in alpine meadow than in other three grassland types; the ratio of root to shoot (R/S) was significantly higher in desert grassland (36.06) than intemperate grassland (16.60), alpine meadow (13.35), and meadow steppe (19.46). The temperate grassland had deeper root distribution than the other three grasslands, with about 91.45% roots distributed in the top 30 cm soil layer. (b) The slopes between log AGB and log BGB in the temperate grassland and meadow steppe were 1.09 and 1, respectively, whereas that in the desert grassland was 1.12, which was significantly different from the isometric allocation relationship. A competitive relationship between AGB and BGB was observed in the alpine meadow with a slope of −1.83, indicating a trade‐off between AGB and BGB in the alpine meadow. (c) A positive productivity–richness relationship existed across the four grassland types, suggesting that the positive productivity–richness relationship might not be affected by the environmental factors at the plant location. Our results provide a new insight for biomass allocation and biodiversity–ecosystem functioning research.

Changes in plant species richness distribution in Tibetan alpine grasslands under different precipitation scenarios

Species richness is the core of biodiversity-ecosystem functioning (BEF) research. Nevertheless, it is difficult to accurately predict changes in plant species richness under different climate scenarios, especially in alpine biomes. In this study, we surveyed plant species richness from 2009 to 2017 in 75 alpine meadows (AM), 199 alpine steppes (AS), and 71 desert steppes (DS) in the Tibetan Autonomous Region, China. Along with 20 environmental factors relevant to species settlement, development, and survival, we first simulated the spatial pattern of plant species richness under current climate conditions using random forest modelling. Our results showed that simulated species richness matched well with observed values in the field, showing an evident decrease from meadows to steppes and then to deserts. Summer precipitation, which ranked first among the 20 environmental factors, was further confirmed to be the most critical driver of species richness distribution. Next, we simulated and compared species richness patterns under four different precipitation scenarios, increasing and decreasing summer precipitation by 20% and 10%, relative to the current species richness pattern. Our findings showed that species richness in response to altered precipitation was grassland-type specific, with meadows being sensitive to decreasing precipitation, steppes being sensitive to increasing precipitation, and deserts remaining resistant. In addition, species richness at low elevations was more sensitive to decreasing precipitation than to increasing precipitation, implying that droughts might have stronger influences than wetting on species composition. In contrast, species richness at high elevations (also in deserts) changed slightly under different precipitation scenarios, likely due to harsh physical conditions and small species pools for plant recruitment and survival. Finally, we suggest that policymakers and herdsmen pay more attention to alpine grasslands in central Tibet and at low elevations where species richness is sensitive to precipitation changes.

Ecosystem responses to exotic earthworm invasion in northern North American forests.

Earth is experiencing a substantial loss of biodiversity at the global scale, while both species gains and losses are occurring at local and regional scales. The influence of these nonrandom changes in species distributions could profoundly affect the functioning of ecosystems and the essential services that they provide. However, few experimental tests have been conducted examining the influence of species invasions on ecosystem functioning. Even fewer have been conducted using invasive ecosystem engineers, which can have disproportionately strong influence on native ecosystems relative to their own biomass. The invasion of exotic earthworms is a prime example of an ecosystem engineer that is influencing many ecosystems around the world. In particular, European earthworm invasions of northern North American forests cause simultaneous species gains and losses with significant consequences for essential ecosystem processes like nutrient cycling and crucial services to humanity like soil erosion control and carbon sequestration. Exotic earthworms are expected to select for specific traits in communities of soil microorganisms (fast-growing bacteria species), soil fauna (promoting the bacterial energy channel), and plants (graminoids) through direct and indirect effects. This will accelerate some ecosystem processes and decelerate others, fundamentally altering how invaded forests function. This project aims to investigate ecosystem responses of northern North American forests to earthworm invasion. Using a novel, synthetic combination of field observations, field experiments, lab experiments, and meta-analyses, the proposed work will be the first systematic examination of earthworm effects on (1) plant communities and (2) soil food webs and processes. Further, (3) effects of a changing climate (warming and reduced summer precipitation) on earthworm performance will be investigated in a unique field experiment designed to predict the future spread and consequences of earthworm invasion in North America. By assessing the soil chemical and physical properties as well as the taxonomic (e.g., by the latest next-generation sequencing techniques) and functional composition of plant, soil microbial and animal communities and the processes they drive in four forests, work packages I-III take complementary approaches to derive a comprehensive and generalizable picture of how ecosystems change in response to earthworm invasion. Finally, in work package IV meta-analyses will be used to integrate the information from work packages I-III and existing literature to investigate if earthworms cause invasion waves, invasion meltdowns, habitat homogenization, and ecosystem state shifts. Global data will be synthesized to test if the relative magnitude of effects differs from place to place depending on the functional dissimilarity between native soil fauna and exotic earthworms. Moving from local to global scale, the present proposal examines the influence of earthworm invasions on biodiversity-ecosystem functioning relationships from an aboveground-belowground perspective in natural settings. This approach is highly innovative as it utilizes the invasion by exotic earthworms as an exciting model system that links invasion biology with trait-based community ecology, global change research, and ecosystem ecology, pioneering a new generation of biodiversity-ecosystem functioning research.

Using root traits to understand temporal changes in biodiversity effects in grassland mixtures

Biodiversity–ecosystem functioning (BEF) studies typically show that species richness enhances community biomass, but the underlying mechanisms remain debated. Here, we combine metrics from BEF research that distinguish the contribution of dominant species (selection effects, SE) from those due to positive interactions such as resource partitioning (complementarity effects, CE) with a functional trait approach in an attempt to reveal the functional characteristics of species that drive community biomass in species mixtures. In a biodiversity experiment with 16 plant species in monocultures, 4‐species and 16‐species mixtures, we used aboveground biomass to determine the relative contributions of CE and SE to biomass production in mixtures in the second, dry year of the experiment. We also measured root traits (specific root length, root length density, root tissue density and the deep root fraction) of each species in monocultures and linked the calculated community weighted mean (CWM) trait values and trait diversity of mixtures to CE and SE. In the second year of the experiment, community biomass, CE and SE increased compared to the first year. The contribution of SE to this positive effect was greater than that of CE. The increased contribution of SE was associated with root traits: SE increased most in communities with high abundance of species with deep, thick and dense roots. In contrast, changes in CE were not related to trait diversity or CWM trait values. Together, these results suggest that increased positive effects of species richness on community biomass in a dry year were mainly driven by increased dominance of deep‐rooting species, supporting the insurance hypothesis of biodiversity. Positive CE indicates that other positive interactions did occur, but we could not find evidence that belowground resource partitioning or facilitation via root trait diversity was important for community productivity in our biodiversity experiment.