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Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity–ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity–productivity relationships. However, the overlooking of the specific role played by key species has limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects. Here, we conducted a grassland diversity–productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production. We grew six plant species in monoculture, as well as in every combination of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half‐density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community‐weighted mean (CWM) of each trait. We further partitioned above‐ground biodiversity effect into complementarity and selection effects. We observed strong positive biodiversity effects on both above‐ground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (Plantago lanceolata) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity–ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

1. Forest productivity may be determined not only by biodiversity but also by environmental factors and stand structure attributes. However, the relative importance of these factors in determining productivity is still controversial for subtropical forests. 2. Based on a large dataset from 600 permanent forest inventory plots across subtropical China, we examined the relationship between biodiversity and forest productivity and tested whether stand structural attributes (stand density in terms of trees per ha, age and tree size) and environmental factors (climate and site conditions) had larger effects on productivity. Furthermore, we quantified the relative importance of environmental factors, stand structure and diversity in determining forest productivity. 3. Diversity, together with stand structure and site conditions, regulated the variability in forest productivity. The relationship between diversity and forest productivity did not vary along environmental gradients. Stand density and age were more important modulators of forest productivity than diversity. 4. Synthesis. Diversity had significant and positive effects on productivity in species rich subtropical forests, but the effects of stand density and age were also important. Our work highlights that while biodiversity conservation is often important, the regulation of stand structure can be even more important to maintain high productivity in subtropical forests.

ContextThe relationship between biodiversity and ecosystem functioning (BEF) has been a central topic in ecology for more than 20 years. While experimental and theoretical studies have produced much knowledge of how biodiversity affects ecosystem functioning, it remains poorly understood how habitat fragmentation affects the BEF relationship.ObjectivesTo develop a framework that connects habitat fragmentation to the BEF relationship from a landscape perspective.MethodsWe reviewed the literature on habitat fragmentation, BEF, and related fields, and developed a framework to analyze how habitat fragmentation affects the BEF relationship through altering biodiversity, environmental conditions, and both, based on the pattern-process-scale perspective in landscape ecology.ResultsOur synthesis of the literature suggests that habitat fragmentation can alter BEF relationship through several processes. First, habitat fragmentation causes the non-random loss of species that make major contributions to ecosystem functioning (decreasing sampling effect), and reduces mutualistic interactions (decreasing complementarity effects) regardless of the changes in species richness. Second, environmental conditions within patches and ecological flows among patches vary significantly with the degree of fragmentation, which potentially contributes to and modulates the BEF relationship.ConclusionsHabitat fragmentation can affect the BEF relationship directly by altering community composition, as well as indirectly by changing environmental conditions within and among habitat patches on both local and landscape levels. The BEF relationship obtained from small plots and over short time periods may not fully represent that in real landscapes that are fragmented, dynamic, and continuously influenced by myriad human activities on different scales in time and space.

We bring together social identity and social exchange perspectives to develop and test a moderated mediation model that sheds light on employees’ perceptions regarding the interrelations between an organization’s external and internal CSR initiatives and their job attitudes and work behaviours. This is important because employees’ sensemaking of CSR motives as being either self-focussed or others-focussed can produce meaningful variations in their job satisfaction and the dimensions of organizational commitment. Also, the consolidation of CSR’s underlying psychological mechanisms can advance our understanding of the processes, contingencies, and outcomes of employees’ perceptions of their employing organization’s CSR initiatives. Our findings indicate that of the two orientations, only external CSR is associated with increased levels of employee commitment through the enhancement of job satisfaction. In particular, job satisfaction was found to fully mediate the impact of external CSR on behavioural commitment and partially mediate its impact on attitudinal commitment. To our surprise, internal CSR has no significant association with job attitudes or work behaviours. We further reveal the complementarity of external and internal CSR orientations; the effect of external CSR on employee outcomes is stronger when employed in concert with internal CSR. Our results contribute to and have implications for both theory and practice.

Understanding how biodiversity influences ecosystem functioning is one of the central goals of modern ecology. The early and often acrimonious debates about the relationship between biodiversity and ecosystem functioning were largely resolved following the advent of a statistical partitioning scheme that decomposed the net effect of biodiversity on ecosystem functioning into a “selection” effect and a “complementarity” effect. Here we show that both the biodiversity effect and its statistical decomposition into selection and complementarity are fundamentally flawed because these methods use a naïve null expectation based on neutrality, likely leading to an overestimate of the net biodiversity effect, and because they fail to account for the nonlinear abundance-ecosystem-functioning relationships widely observed in nature. Furthermore, under nonlinearity no such statistical scheme can be devised to partition the biodiversity effect. We also present an alternative approach that provides a more reasonable starting point for estimating biodiversity effects. Overall, our results suggest that all studies conducted since the early 1990s are likely to have overestimated the positive effects of biodiversity on ecosystem functioning.

Climate change and biodiversity loss are expected to simultaneously affect ecosystems, however research on how each driver mediates the effect of the other has been limited in scope. The multiple stressor framework emphasizes non-additive effects, but biodiversity may also buffer the effects of climate change, and climate change may alter which mechanisms underlie biodiversity–function relationships. Here, we performed an experiment using tank bromeliad ecosystems to test the various ways that rainfall changes and litter diversity may jointly determine ecological processes. Litter diversity and rainfall changes interactively affected multiple functions, but how depends on the process measured. High litter diversity buffered the effects of altered rainfall on detritivore communities, evidence of insurance against impacts of climate change. Altered rainfall affected the mechanisms by which litter diversity influenced decomposition, reducing the importance of complementary attributes of species (complementarity effects), and resulting in an increasing dependence on the maintenance of specific species (dominance effects). Finally, altered rainfall conditions prevented litter diversity from fueling methanogenesis, because such changes in rainfall reduced microbial activity by 58%. Together, these results demonstrate that the effects of climate change and biodiversity loss on ecosystems cannot be understood in isolation and interactions between these stressors can be multifaceted.

Plant productivity often increases with species richness, but the mechanisms explaining this diversity–productivity relationship are not fully understood. We tested if plant–soil feedbacks (PSF) can help to explain how biomass production changes with species richness. Using a greenhouse experiment, we measured all 240 possible PSFs for 16 plant species. At the same time, 49 plant communities with diversities ranging from one to 16 species were grown in replicated pots. A suite of plant community growth models, parameterized with (PSF) or without PSF (Null) effects, was used to predict plant growth observed in the communities. Selection effects and complementarity effects in modeled and observed data were separated. Plants created soils that increased or decreased subsequent plant growth by 25% ± 10%, but because PSFs were negative for C₃ and C₄ grasses, neutral for forbs, and positive for legumes, the net effect of all PSFs was a 2% ± 17% decrease in plant growth. Experimental plant communities with 16 species produced 37% more biomass than monocultures due to complementarity. Null models incorrectly predicted that 16-species communities would overyield due to selection effects. Adding PSF effects to Null models decreased selection effects, increased complementarity effects, and improved correlations between observed and predicted community biomass. PSF models predicted 26% of overyielding caused by complementarity observed in experimental communities. Relative to Null models, PSF models improved the predictions of the magnitude and mechanism of the diversity–productivity relationship. Results provide clear support for PSFs as one of several mechanisms that determine diversity–productivity relationships and help close the gap in understanding how biodiversity enhances ecosystem services such as biomass production.

Biodiversity effects on ecosystem functioning can be partitioned into complementarity effects, driven by many species, and selection effects, driven by few. Selection effects occur through interspecific abundance shifts (dominance) and intraspecific shifts in functioning. Complementarity and selection effects are often calculated for biomass, but very rarely for secondary productivity, that is, energy transfer to higher trophic levels. We calculated diversity effects for three functions: aboveground biomass, insect herbivory and pathogen infection, the latter two as proxies for energy transfer to higher trophic levels, in a grassland experiment (PaNDiv) manipulating species richness, functional composition, nitrogen enrichment, and fungicide treatment. Complementarity effects were, on average, positive and selection effects negative for biomass production and pathogen infection and multiple species contributed to diversity effects in mixtures. Diversity effects were, on average, less pronounced for herbivory. Diversity effects for the three functions were not correlated, because different species drove the different effects. Benefits (and costs) from growing in diverse communities, be it reduced herbivore or pathogen damage or increased productivity either due to abundance increases or increased productivity per area were distributed across different plant species, leading to highly variable contributions of single species to effects of diversity on different functions. These results show that different underlying ecological mechanisms can result in similar overall diversity effects across functions.

Background and aims Maize/legume intercropping leads to overyielding and maintains soil nutrients. Rhizobium inoculation in maize/legume intercropping enhances soil nitrogen; however, its effects on overyielding and other soil nutrients in long-term intercropping systems is not well understood. Methods We conducted a split-split-plot experiment with three factors in northwest China since 2009. The main plot treatments were without or with rhizobium inoculation in faba bean (-Rhizobium, +Rhizobium), while the sub-plot treatments were five nitrogen-application rates and the sub-sub-plot treatments were cropping system (monocultures of faba bean, maize and faba bean/maize intercropping). During 2018-2020, we measured the yield, soil nutrients in the 0-20 cm topsoil, calculated biodiversity effects, and quantified interspecific interaction of intercropping using the relative interaction index. Results The grain yields in intercropping with treatments of -Rhizobium and + Rhizobium increased by 8.9% and 32%, respectively, compared with the corresponding weighted means of monocultures. Rhizobium inoculation increased the land-equivalent ratio at high nitrogen application. The combination of rhizobium inoculation and nitrogen application significantly enhanced the complementarity effect and relative interaction index of maize. With rhizobium inoculation, intercropping increased the soil Olsen P concentration by 13.9-59.9%, compared with the corresponding weighted means of monocultures which may be associated with interspecific facilitation, indicated by relative interaction index of maize. Conclusions Our study shows that rhizobium inoculation increased yield advantages and soil Olsen P concentration via enhanced interspecific facilitation of faba bean on maize in the intercropping system. Rhizobium inoculation can be used as an efficient strategy to enhance the benefits of intercropping, especially in low-fertility soil.

Increasing evidence shows that biodiversity–ecosystem functioning relationships (BEFs) become stronger as forests develop, but much of the evidence is drawn from experiments (less than 30 years). How the biodiversity effects vary with stand development stages remains largely unexplored. Using a large temperate forest dataset with 2392 permanent plots in northeastern China, we examined the relationships between biodiversity (i.e. tree species richness, functional diversity, and functional composition) and aboveground biomass (AGB) across different development stages of temperate forests (covering all stages from young to overmature forests). Specifically, the complementarity and mass‐ratio effects across different forest development stages were evaluated to elucidate emerging patterns that explain ecosystem functioning. We observed positive BEFs using both tree species richness and functional diversity, but these positive effects decreased with forest development. However, the effects of community‐weighted mean (CWM) on AGB showed two peaks in young and mature stands. Interestingly, the effects of CWM on AGB became larger than the effects of functional diversity after the forests developed to near‐mature/mature stands, indicating that BEFs are driven by mass‐ratio effects (i.e. dominant tree species) rather than niche complementarity in old stands. The high AGB in young stands was characterized by tree species with high resource acquisition ability, however, in old stands, it was associated with tree species with both high resource acquisition ability and conservative traits. Our findings indicate how the developmental stage influences the effects of biodiversity on ecosystem functioning in natural forests. The findings tentatively advocate for a mechanistic framework of BEFs covering all developmental stages of temperate forests, which could facilitate the formulation of effective strategies for enhancing ecosystem functioning at different development stages.