The combinations of taxonomic, functional and phylogenetic method have
been frequently advocated to assess how changes in biodiversity affect
community structure and ecosystem function. Using a large grassland
community database involving 917 species and 118 sites across the
eastern and central Tibetan plateau, we found an overall positive
biodiversity-productivity relationship in species', functional and
phylogenetic space. The relationship, however, was nonlinear, in which
biodiversity explained better the variation in community biomass when
species diversity was more than a threshold, showing a weak effect of
biodiversity on ecosystem function in low species diversity communities.
We also found a filled triangle for the limit of the relationship
between species' and functional diversity, implying that functional
diversity differs significantly among communities when their species
diversity is low but finally converges to be a constant with increasing
communities' species diversity. Our research suggests that multiple
niche processes may structure the Tibetan grassland communities, and
their forces tend to balance in high-biodiversity communities.