Complementarity effects among plant–pollinator interactions can enhance community seed production in semi-arid natural grasslands

Niche complementarity (i.e., complementarity effect) or differences in competitive ability (i.e., selection effect) are the two main mechanisms underlying the biodiversity and ecosystem functioning relationships within a single trophic level. However, few studies have explored such operating mechanisms across multitrophic levels and ecosystem functions, such as pollination. In this large grassland biodiversity study in Inner Mongolia, we partitioned the net biodiversity effect on seed production into the complementarity and selection effects and related these effects to functional diversity and the composition of flowering plant traits, and a range of plant–pollinator network parameters. The positive effect of plant species richness on the complementarity effects overwhelmed the negative effect on the selection effects. Hence, plant diversity positively impacted the net biodiversity effects. In addition, the net biodiversity and complementarity effects were increased in plant communities dominated by species with long inflorescences, suggesting that the facilitative effects of these dominant species attract more pollinators for other species. Furthermore, the complementarity effect increased with decreasing niche overlap of pollinator species, indicating complementary resource use among plant–pollinator interactions. Collectively, our findings highlight the importance of multitrophic interactions in maintaining multitrophic ecosystem functions.