Study On The Determinants Of Abundance And Productivity In Sub-Alpine Meadow During Succession Based On Functional Traits

Functional traits can parse determinants of species abundance and productivity,but the current study did not consider traits-abundance relationships and diversity-productivity relationships along environmental gradients.This restricts the explanatory role of functional traits on the determinants of species abundance and productivity,which can be solved by exploring the relationships between traits and abundance and the relationships between diversity and productivity along the secondary succession gradients.Here,in naturally developed long term sub-alpine meadows(4-year,6-year,10-year,13 years and at least 40years)in the Qinghai-Tibetan Plateau,we investigated the species abundance of these communities,measured aboveground biomass of the communities and six traits(specific leaf area,seed mass,seed germination rate,height,leaf proline content and photosynthesis rate)of various plants,calculated two functional diversity indices: the community weighted mean trait values(CWM)and the Rao’s quadratic entropy(RaoQ)which are highly correlated to functional traits of dominating species and variety of functional diversity among all species.And the ANCOVA model was used to research the relationships between traits and abundance in a successional chronosequence of the sub-alpine meadow plant communities,then the standard effect size index(SES)was obtained by the observed value of functional diversity and mean value of functional diversity of the simulated null community to explore the relative contributions of niche theory and neutral theory to species abundance.At the same time,the correlation analysis was used to study the relationships between species richness and productivity to testify whether positive relationships between diversity and productivity can still exist in naturally developed long term communities.Then,a variance partitioning analysis was used to test the relative contributions of species richness,functional traits of dominating species and functional diversity among all species to productivity along the succession,and analyzed the impact of selection effect and niche complementarity effect on productivity.The main results are as follows:1)In late-successional meadows(10-year,13-year and 40-years meadow),abundant species had higher values for seed mass,seed germination rate,and specific leaf area,but had lower values for height,photosynthesis rate,and leaf proline content than rarer species.The opposite patterns of relationships between traits and abundance were observed for earlysuccessional meadows(4-year and 6-year meadow).2)The SESs of both the early-and late-successional communities were significantly greater than or less than zero,indicating that the plant traits were significantly convergent or divergent during succession.So the dominant role for niche processes but not neutral processes in determining the variations in species abundance.3)There were strong positively relationships between diversity and productivity in the natural sub-alpine meadow communities along the succession.And the CWM explained a large proportion(54-80%)of the variation in productivity during succession,whereas species diversity and RaoQ explained much less(24-48% for species richness and 0-40%for RaoQ respectively).