Comparing the effects of companion species diversity and the dominant species (Stipa grandis) genotypic diversity on the biomass explained by plant functional trait

Plant diversity exerts significant effects on ecosystem functioning. However, it remains unclear that whether the ecological consequences of genotypic diversity of the dominant species is similar to that of species diversity. In this study, diversity effects on biomass of 12 companion species and 12 genotypes of the dominant species (Stipa grandis) in the Inner Mongolia Steppe of China were examined by two independent diversity experiments. In order to explain the diversity effects, seven plant functional traits for each species or each genotype of S. grandis per mixture treatment were measured and their Rao's quadratic entropy (FDQ) was estimated. There was significantly positive net species diversity effect on aboveground biomass, which was mainly contributed by complementarity effect; however, net diversity effects were not significant in genotypic diversity experiment. The FDQ among S. grandis genotypes was significantly lower than that among the companion species, and the relatively lower FDQ would increase niche overlap and limit complementarity effect among genotypes. Neither species diversity nor genotypic diversity of S. grandis showed significant influences on belowground biomass, suggesting the non-consistent results of diversity effect between belowground and aboveground systems. The present finding highlighted the species diversity effects on biomass, the role of FDQ on explaining complementarity effect by niche overlap or resource use efficient.