Non-neutral Assembling Mechanism Of The Sub-alpine Meadow Plant Communities

Species coexistence and community assembly mechanism is a core issue in ecology. Niche theory and neutral theory are two important theories to answer the question, but they differ in the importance of species traits in determining species coexistence and community assembly. Niche theory and neutral theory address niche differentiation (deterministic factors) and random factors to explain the mechanisms of species coexistence respectively. Here we examined the roles of the two theories in assembling the sub-alpine meadow plant communities of the five abandoned grassland in the eastern edge of Qinghai-Tibetan Plateau. The five meadows had been excluded from farming for7years,10years,12years,22years and32years respectively. We use the broken stick model, niche priority occupation model, the lognormal model, Zipf model, the Mandelbrot model etc. to fit the species-abundance distributions in these. meadows. We also examined the relationship between several functional traits of plant leaves, the equivalence of plant height with species abundance, the relationship between soil nutrients and Simpson index, and the equivalence of biomass and abundance, aiming to explore the strategies of plants in these meadows, and to explore the relative importance of the two theory. The main results are as follows:(1) In addition to plant leaf C content, N content of plants in meadows of age12and leaf N content of plants in meadows of age32are positively correlated with plant abundance, SLA, LDMC, N, P, C content of leaves plant height do not correct with species abundance in other meadows.(2) The variance and skewness of log-transformed abundance and biomass are not distributed around the Y=X line, showing a random pattern between them.(3) Soil N content in5cm depth, C content in5cm depth and nitrate nitrogen content in20cm depth can significantly affect the observed species diversity compared to other considered environmental factors.(4) At the early stages of community succession, niche occupation model compared to other models can better explain the observed quadrat species abundance pattern, while the Mandelbrot model performs better as succession proceeds.