Biodiversity losses on a global scale adversely impact terrestrial ecosystem services. However, the mechanisms driving productivity in diverse communities remain contested. In a large biodiversity manipulation experiment, we test the extent to which resource partitioning explains diversity effects on plant productivity. We manipulated plant diversity, selecting six plant species each from three families (Poacea, Asteracae, and Fabaceae) commonly represented in native tallgrass prairies in experiments established in spring 2018 at the University of Kansas field station (Jefferson Co., KS). We manipulated species richness by randomly selecting 1, 2, 3, or 6 species within family. To increase functional and phylogenetic dissimilarity we assembled plots by randomly selecting species from different families containing 2, 3, and 6 species. Precipitation is altered to 50% and 150% of ambient conditions through the installation of rainfall manipulation shelters. Overall, treatment combinations are replicated 12 to 36 times, totaling 240-2.25m2 plots. To quantify productivity we sampled total plot cover monthly throughout the 2019 growing season and at peak biomass in 2018. We partition the net biodiversity effects into the complementary effect (when species productivity is higher than expected based on weighted monoculture yields) and the selection effect (when productivity is driven by a dominant species).
Results/Conclusions
In 2018, the net biodiversity effect increased with richness, but the relationship was weak. In 2019, we observed a significant positive effect in all mixtures (p<0.05) and a significant linear increase with species richness (r2=0.31, p<0.0001), indicating the emergence of diversity effects very early in community assembly. Differences between precipitation treatments have yet to manifest. While we observed positive selection effects, the relationship between complementary effects and richness is stronger in year two, accounting for more of the net biodiversity effect on productivity. Functional trait diversity, as estimated by Rao’s quadratic entropy, with data from the TRY database, significantly positively predicted the complementary effect (r2=0.07, p=0.0007) in 2019, suggesting increasing diversity of resource acquisition traits may in part explain complementary effects. We observed a high degree of variation in the extent to which the selection effect contributed to the overall net biodiversity effect over the 2019 growing season, with the complementary effect contributing the greatest to the net biodiversity effect in the beginning and end of the growing season. This pattern suggests over the growing season plant phenology and temporal resource partitioning may also contribute to the net effect of biodiversity on plant production.