Relationship between functional diversity and productivity in meadow and marsh plant communities

Aims There are two hypotheses on the mechanism of functional diversity driving ecosystem processes: one is the mass ratio hypothesis based on dominant species, and the other is the diversity hypothesis based on ecological niche. Both hypotheses have been supported by different studies, but their applicability and universality are still controversial. Our objective was to clarify whether the explanatory ability of these two hypotheses to productivity is influenced by the existence of intensive environmental filtering, which was flooding in this study.
Methods Three meadow communities and three marsh communities were studied over two years in the Momoge National Nature Reserve in western Jilin Province. The aboveground biomass, species diversity (species richness and Shannon-Weaver index), functional diversity (community weighted mean and Rao’s quadratic entropy), and several environmental factors were compared among different communities. The functional diversity was calculated for seven plant traits. The relationship between diversity index and aboveground biomass was explored by simple linear regression analysis and multiple linear regression analysis with stepwise method.
Important findings Both Rao’s quadratic entropy and community weighted mean could explain more variation in community productivity than species diversity. Furthermore, both mass ratio hypothesis and diversity hypothesis supported the diversity-productivity relationship. However, the mass ratio hypothesis may play a relatively greater role than the diversity hypothesis, indicating that the ecosystem function mainly depended on the functional traits of dominant species. Intensive environment filtering in terms of flooding affected the diversity-productivity relationship. The mass ratio hypothesis based on community weighted mean explained more variation of the productivity in meadow communities without flooding filtering, while diversity hypothesis based on Rao’s quadratic entropy explained more variation of the productivity in marsh communities with flooding filtering.