The functional diversity-productivity relationship of woody plants is climatically sensitive.

Plot-scale experiments indicate that functional diversity (FD) plays a pivotal role in sustaining ecosystem functions such as net primary productivity (NPP). However, the relationships between functional diversity and NPP across larger scale under varying climatic conditions are sparsely studied, despite its significance for understanding forest-atmosphere interactions and informing policy development. Hence, we examine the relationships of community-weighted mean (CWM) and functional dispersion (FDis) of woody plant traits on NPP across China and if such relationships are modulated by climatic conditions at the national scale. Using comprehensive datasets of distribution, functional traits, and productivity for 9120 Chinese woody plant species, we evaluated the distribution pattern of community-weighted mean and functional dispersion (including three orthogonal trait indicators: plant size, leaf morphology, and flower duration) and its relationships with NPP. Finally, we tested the effects of climatic conditions on community-weighted mean/functional dispersion-NPP relationships. We first found overall functional diversity-NPP relationships, but also that the magnitude of these relationships was sensitive to climate, with plant size community-weighted mean promoting NPP in warm regions and plant size functional dispersion promoting NPP in wet regions. Second, warm and wet conditions indirectly increased NPP by its positive effects on community-weighted mean or functional dispersion, particularly through mean plant size and leaf morphology. Our study provides comprehensive evidence for the relationships between functional diversity and NPP under varying climates at a large scale. Importantly, our results indicate a broadening significance of multidimensional plant functional traits for woody vegetation NPP in response to rising temperatures and wetter climates. Restoration, reforestation actions and natural capital accounting need to carefully consider not only community-weighted mean and functional dispersion but also their interactions with climate, to predict how functional diversity may promote ecosystem functioning under future climatic conditions.

Dear neighbor: Trees with extrafloral nectaries facilitate defense and growth of adjacent undefended trees.

Plant diversity can increase productivity. One mechanism behind this biodiversity effect is facilitation, which is when one species increases the performance of another species. Plants with extrafloral nectaries (EFNs) establish defense mutualisms with ants. However, whether EFN plants facilitate defense of neighboring non-EFN plants is unknown. Synthesizing data on ants, herbivores, leaf damage, and defense traits from a forest biodiversity experiment, we show that trees growing adjacent to EFN trees had higher ant biomass and species richness and lower caterpillar biomass than conspecific controls without EFN-bearing neighbors. Concurrently, the composition of defense traits in non-EFN trees changed. Thus, when non-EFN trees benefit from lower herbivore loads as a result of ants spilling over from EFN tree neighbors, this may allow relatively reduced resource allocation to defense in the former, potentially explaining the higher growth of those trees. Via this mutualist-mediated facilitation, promoting EFN trees in tropical reforestation could foster carbon capture and multiple other ecosystem functions.

Genetic richness affects trait variation but not community productivity in a tree diversity experiment.

Biodiversity-ecosystem functioning experiments found that productivity generally increases with species richness, but less is known about effects of within-species genetic richness and potential interactions between the two. While functional differences between species can explain species richness effects, empirical evidence regarding functional differences between genotypes within species and potential consequences for productivity is largely lacking. We therefore measured within- and among-species variation in functional traits and growth and determined stand-level tree biomass in a large forest experiment factorially manipulating species and genetic richness in subtropical China. Within-species variation across genetic seed families, in addition to variation across species, explained a substantial amount of trait variation. Furthermore, trait responses to species and genetic richness varied significantly within and between species. Multivariate trait variation was larger among individuals from species mixtures than those from species monocultures, but similar among individuals from genetically diverse vs genetically uniform monocultures. Correspondingly, species but not genetic richness had a positive effect on stand-level tree biomass. We argue that identifying functional diversity within and among species in forest communities is necessary to separate effects of species and genetic diversity on tree growth and community productivity.