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Understanding how species interactions drive succession is a key issue in ecology. In this study we show the utility of combining the concepts and methodologies developed within the biodiversity-–ecosystem functioning research program with J. H. Connell and R. O. Slatyer's classic framework to understand succession in assemblages where multiple interactions between early and late colonists may include both inhibitory and facilitative effects. We assessed the net effect of multiple species interactions on successional changes by manipulating the richness, composition, and abundance of early colonists in a low-shore assemblage of algae and invertebrates of the northwestern Mediterranean. Results revealed how concomitant changes in species richness and abundance can strongly alter the net effect of inhibitory vs. facilitative interactions on succession. Increasing richness of early colonists inhibited succession, but only under high levels of initial abundance, probably reflecting the formation of a highly intricate matrix that prevented further colonization. In contrast, increasing initial abundance of early colonists tended to facilitate succession under low richness. Thus, changes in abundance of early colonists mediated the effects of richness on succession.

Biodiversity-ecosystem functioning (BEF) research has shown that ecosystem functioning and stability are closely linked to biodiversity. A cornerstone of this field is the BEF-China research platform, i.e. the world’s largest forest biodiversity experiment in subtropical China. It has demonstrated that tree diversity enhances productivity, carbon sequestration and ecosystem stability. However, the strength of these positive tree diversity effects varies widely across forests, possibly because higher trophic levels (such as herbivores and predators) mediate how biodiversity influences ecosystem functioning. To better understand how tree diversity influences higher trophic levels and their contributions to forest functioning, the German Research Foundation (DFG) is funding the project MultiTroph . MultiTroph quantifies species interactions and integrates them into food webs to understand when and why ecosystem functions change or destabilise with species loss. We expect that trophic interaction networks reveal how species share or separate their ecological roles, with more niche overlap in species-rich forests and more niche specialisation in species-poor forests. Here, we outline our conceptual framework and research goals. We are convinced that MultiTroph will expand existing BEF research and provide a more holistic understanding of the role of multi-trophic food webs in forest ecosystems.

Preserving biodiversity and ecosystem function in the Anthropocene is one of humanity's greatest challenges. Ecosystem‐based management and area closures are considered an effective way to maintain ecological processes, especially in marine systems. Although there is strong evidence that such measures positively affect community structure, their impact on the rate of key ecological processes remains unclear. Here, we provide evidence that marine protected areas enhance herbivory rates on coral reefs via direct and indirect pathways. Using meta‐analysis and a path‐analytical framework, we demonstrate that, on average, protected areas increase the species richness of herbivorous fishes, which, in turn, enhances browsing rates on macroalgae. However, in all three regions studied (the Atlantic, Indian, and Pacific Ocean), a small subset of the herbivore assemblage accounted for the majority of browsing. Our results therefore indicate that ecosystem functioning on coral reefs may respond positively to both area closures and the protection of key species.

Human‐caused declines in biodiversity have stimulated intensive research on the consequences of biodiversity loss for ecosystem services and policy initiatives to preserve the functioning of ecosystems. Short‐term biodiversity experiments have documented positive effects of plant species richness on many ecosystem functions, and longer‐term studies indicate, for some ecosystem functions, that biodiversity effects can become stronger over time. Theoretically, a biodiversity effect can strengthen over time by an increasing performance of high‐diversity communities, by a decreasing performance of low‐diversity communities, or a combination of both processes. Which of these two mechanisms prevail, and whether the increase in the biodiversity effect over time is a general property of many functions remains currently unclear. These questions are an important knowledge gap as a continuing decline in the performance of low‐diversity communities would indicate an ecosystem‐service debt resulting from delayed effects of species loss on ecosystem functioning. Conversely, an increased performance of high‐diversity communities over time would indicate that the benefits of biodiversity are generally underestimated in short‐term studies. Analyzing 50 ecosystem variables over 11 years in the world's largest grassland biodiversity experiment, we show that overall plant diversity effects strengthened over time. Strengthening biodiversity effects were independent of the considered compartment (above‐ or belowground), organizational level (ecosystem variables associated with the abiotic habitat, primary producers, or higher trophic levels such as herbivores and pollinators), and variable type (measurements of pools or rates). We found evidence that biodiversity effects strengthened because of both a progressive decrease in functioning in species‐poor and a progressive increase in functioning in species‐rich communities. Our findings provide evidence that negative feedback effects at low biodiversity are as important for biodiversity effects as complementarity among species at high biodiversity. Finally, our results indicate that a current loss of species will result in a future impairment of ecosystem functioning, potentially decades beyond the moment of species extinction.

Aim: Climate change affects forest functioning not only through direct physiological effects such as modifying photosynthesis and growing season lengths, but also through indirect effects on community composition related to species extinctions and colonizations. Such indirect effects remain poorly explored in comparison with the direct ones. Biodiversity-ecosystem functioning (BEF) studies commonly examine the effects of species loss by eliminating species randomly. However, species extinctions caused by climate change will depend on the species' vulnerability to the new environmental conditions, thus occurring in a specific, non-random order. Here, we evaluated whether successive tree species extinctions, according to their vulnerability to climate change, impact forest functions differently than random species losses. Location: Eleven temperate forests across a gradient of climatic conditions in central Europe. Methods: We simulated tree community dynamics with a forest succession model to study the impact of species loss on the communities' aboveground biomass, productivity and temporal stability. Tree species were removed from the local pool (1) randomly, and according to (2) their inability to be recruited under a warmer climate or (3) their increased mortality under drier conditions. Results: Results showed that non-random species loss (i.e., based on their vulnerability to warmer or drier conditions) changed forest functioning at a different rate, and sometimes direction, than random species loss. Furthermore, directed extinctions, unlike random, triggered tipping points along the species loss process where forest functions were strongly impacted. These tipping points occurred after fewer extinctions in forests located in the coldest areas, where ecosystem functioning relies on fewer species. Main conclusions: We showed that the extinction of species in a deterministic and mechanistically motivated order, in this case the species vulnerability to climate change, strengthens the selection effect of diversity on ecosystem functioning. BEF studies exploring the impact of species loss on ecosystem functioning using random extinctions thus possibly underestimate the potential effect of biodiversity loss when driven by a directional force, such as climate change.

Research on the functional importance of biodiversity, motivated by global species loss, has documented that plant species richness affects many plant‐related ecosystem functions. Less is known about the effects of plant species richness on functions related to higher trophic levels, such as the consumption of biomass by animals, that is, herbivory. Previous studies have shown positive, neutral, or negative effects of plant species richness on herbivory. In the framework of a grassland biodiversity experiment (the Jena Experiment), we investigated herbivory (the proportion of leaf area damaged and the amount of leaf biomass consumed by arthropod herbivores) along two experimental gradients of plant species richness ranging from 1 to 60 species (Main Experiment) and from 1 to 8 species (Trait‐Based Experiment) biannually for five and three years, respectively. Additionally, plant functional diversity, based on traits related to plant growth, was manipulated as the number of functional groups in a community (Main Experiment) or a gradient of functional trait dissimilarity (Trait‐Based Experiment). Herbivory at the level of plant communities ranged from 0% to 31% (0 and 33.8 g/m2) in the Main Experiment and 0% to 8% (0 and 13.7 g/m2) in the Trait‐Based Experiment, and it was on average higher in summer than in spring. For both experimental gradients and all years investigated, we found a consistent increase in damaged leaf area and consumed biomass with increasing plant species richness. As mechanistic explanations for effects of plant species richness, we propose changes in plant quality and herbivore communities. The presence of specific plant functional groups significantly affected herbivory, likely related to traits affecting plant defense and nutritional value, but we found little evidence for effects of plant functional diversity. The general positive relationship between plant species richness and herbivory might contribute to effects of plant species richness on other ecosystem functions such as productivity and nutrient mineralization and can cascade up the food web also affecting higher trophic levels.

In plant communities, higher levels of taxonomic richness are often shown to be more efficient at utilization of limiting resources due to resource partitioning among taxa. While resource partitioning is also thought to be important in consumer communities, consumers also exhibit more complex interactions like omnivory. Omnivory is generally thought to reduce the effects of consumer richness on the consumption of prey resources; however, empirical tests of this prediction are rare. Here, we report the results of 2 complementary studies to test the hypothesis that omnivory reduces the positive effects of consumer taxonomic richness on prey resource consumption. First, we analyzed data from a dataset consisting of 1,100 freshwater lakes across the continental United States. We show that the relationship between consumer taxonomic richness and the summed biomass of resource prey (phytoplankton) is independent of the proportion of zooplankton (consumers) that are omnivores. However, consumption rates were not explicitly measured in this dataset so that we conducted in situ feeding experiments in 37 lakes near Ann Arbor, MI, USA, to measure omnivorous consumption (Omni) as the amount of smaller microzooplankton (<200 μm) consumed by larger nonherbivorous mesozooplankton. We also measured the amount of phytoplankton consumption (G) across a gradient of zooplankton taxonomic richness (zpSR). We showed that there was a positive association between zpSR and G, suggesting that G was increased by zooplankton diversity. However, the effects of zooplankton diversity on the G are not altered by the level of Omni among zooplankton. Although omnivory does not influence the effects of consumer diversity on prey consumption, we do not negate the impacts of omnivory on other ecosystem functions in aquatic systems. We attempt to address a question that is of general interest to the field of ecology, especially of aquatic ecology, because omnivory is known to be common in aquatic systems.

Questions Despite our increased understanding of how climate change influences plant phenology, it remains poorly understood whether diversity loss could alter phenology as well. Here we investigated the following: (a) do changes in plant diversity affect leaf‐out and flowering dates for woody species; (b) which group of variables are more important in influencing leaf‐out and flowering dates, abiotic variables (soil variables) or biotic variables (plant diversity)? Study site A subtropical forest in the Biodiversity–Ecosystem Functioning Experiment of China, located in Jiangxi Province, China. Methods Species were planted in various combinations to create plots with varying tree richness: 1, 2, 4, 8, 16 or 24 species. We monitored leaf‐out and flowering dates of eight randomly selected species in 17 plots in 2018. A linear model was used to test whether species diversity was a predictor of leaf‐out/flowering times for each species. We then fit linear mixed‐effects models to assess the combined influence of species diversity, soil Total Carbon and Total Nitrogen on the overall community. Results In the low‐diversity plots, we found two species leafing out earlier, one leafing out later and four showing no significant difference. Leaf‐out date advanced an average of 0.3 days per species lost. Of all the biotic and abiotic predictor variables, Total Nitrogen was the only one significantly correlated with leaf‐out date. No significant correlation was found between species diversity and flowering date for any of the species. Conclusions Our study provides the first empirical evidence concerning the effects of biodiversity loss on plant spring phenology for woody species. Our findings illustrate that fluctuation in plant diversity could alter the timing of leaf‐out and that abiotic variables may be more important than biotic variables in determining leaf‐out dates in subtropical forest. Overall, declining diversity may exacerbate the phenological changes attributed to rising global temperatures. We investigated whether phenology shifts in response to biodiversity loss in a subtropical forest, and we found diverging shifts in spring phenology, with leaf‐out date advancing an average of 0.3 days per species lost. Our findings indicate that declines in diversity could further exacerbate the phenological changes attributed to rising global temperatures.

The capacity of forests to sequester carbon in both above‐ and belowground compartments is a crucial tool to mitigate rising atmospheric carbon concentrations. Belowground carbon storage in forests is strongly linked to soil microbial communities that are the key drivers of soil heterotrophic respiration, organic matter decomposition and thus nutrient cycling. However, the relationships between tree diversity and soil microbial properties such as biomass and respiration remain unclear with inconsistent findings among studies. It is unknown so far how the spatial configuration and soil depth affect the relationship between tree richness and microbial properties. Here, we studied the spatial distribution of soil microbial properties in the context of a tree diversity experiment by measuring soil microbial biomass and respiration in subtropical forests (BEF‐China experiment). We sampled soil cores at two depths at five locations along a spatial transect between the trees in mono‐ and hetero‐specific tree pairs of the native deciduous species Liquidambar formosana and Sapindus saponaria . Our analyses showed decreasing soil microbial biomass and respiration with increasing soil depth and distance from the tree in mono‐specific tree pairs. We calculated belowground overyielding of soil microbial biomass and respiration – which is higher microbial biomass or respiration than expected from the monocultures – and analysed the distribution patterns along the transect. We found no general overyielding across all sampling positions and depths. Yet, we encountered a spatial pattern of microbial overyielding with a significant microbial overyielding close to L. formosana trees and microbial underyielding close to S. saponaria trees. We found similar spatial patterns across microbial properties and depths that only differed in the strength of their effects. Our results highlight the importance of small‐scale variations of tree–tree interaction effects on soil microbial communities and functions and are calling for better integration of within‐plot variability to understand biodiversity–ecosystem functioning relationships.

Nitrogen (N) deposition, as one of the global change drivers, can alter terrestrial plant diversity and ecosystem function. However, the response of the plant diversity–ecosystem function relationship to N deposition remains unclear. On one hand, in the previous studies, taxonomic diversity (i.e., species richness, SR) was solely considered the common metric of plant diversity, compared to other diversity metrics such as phylogenetic and functional diversity. On the other hand, most previous studies simulating N deposition only included two levels of control versus N enrichment. How various N deposition rates affect multidimensional plant diversity–ecosystem function relationships is poorly understood. Here, a field manipulative experiment with a N addition gradient (0, 1, 2, 4, 8, 16, 32, and 64 g N m−2 yr−1) was carried out to examine the effects of N addition rates on the relationships between plant diversity metrics (taxonomic, phylogenetic, and functional diversity) and ecosystem production in a temperate steppe. Production initially increased and reached the maximum value at the N addition rate of 47 g m−2 yr−1, then decreased along the N-addition gradient in the steppe. SR, functional diversity calculated using plant height (FDis-Height) and leaf chlorophyll content (FDis-Chlorophyll), and phylogenetic diversity (net relatedness index, NRI) were reduced, whereas community-weighted means of plant height (CWMHeight) and leaf chlorophyll content (CWMChlorophyll) were enhanced by N addition. N addition did not affect the relationships of SR, NRI, and FDis-Height with production but significantly affected the strength of the correlation between FDis-Chlorophyll, CWMHeight, and CWMChlorophyll with biomass production across the eight levels of N addition. The findings indicate the robust relationships of taxonomic and phylogenetic diversity and production and the varying correlations between functional diversity and production under increased N deposition in the temperate steppe, highlighting the importance of a trait-based approach in studying the plant diversity–ecosystem function under global change scenarios.