A Study On Mechanism Of Plant Community Assembly In Qinghai-Tibetan Alpine Meadow

The species coexistence and community assembly mechanisms is the primary question in community ecology study. Both niche theory and neutral theory are important theories for explaining this question, but they have a diverge about the necessity and importance of species traits in determining species coexistence and community assembly mechanism. Niche theory assumes niche differences and trade-offs mechanism are an essential mechanism allowing interacting species to coexist and determine the species abundance distributions(SAD); In neutral theory, all individuals are assumed to be functionally equivalent, the coexistence of species results from stochastic ecological and evolutionary processes acting on both local and regional scales. We used different models that represent deterministic and stochastic progress respectively to fit the observed SAD of our study fields in Qinghai-Tibetan Alpine Meadow. The aims of our study is to empirically test whether the SAD in these prairies consistent with neutral theory along a successional gradient? Furthermore, we combined with leaf traits (LDMC,SLA,LNC) to discuss the relative importance of niche and neutral processes as drivers of community assembly within plant communities. As a result, we found that:(1) Through goodness of fit method there is no significant difference (P>0.05) between predictions of all the models that selected and observed SAD in the community along the succession gradients (9,11,21 and 31 years after abandonment) except the community aged 6 after abandonment. But in least square fit method, there is no significant difference (P<0.05) between predictions of all the models that selected and observed SAD in the succession gradients (6,9,11,21 and 31 years after abandonment). And Geometric series model is better fitted along succession gradients. However, Log-series model did not fit SAD aged 11 after abandonment by both two goodness-of-fit methods. This results showed that fit result depends on which goodness-of-fit measurement is used.(2) LDMC showed a significant increase with field age (r=0.834, p<0.05), while SLA showed the opposite trend (r= -0.752,p>0.05), LNC have no relationship with fild age (r=0.185,p=0.05). LDMC and species abundance have the significant positive relationship in the community aged 31 after abandonment. But the corelation is insignificant between species abundance and the others leaf traits, no common variation trends along succession gradients appeared at the same time.In a word, Our results indicated that species traits difference was a key factor to determine species coexistence and community assembly mechanism, but stochastic processes play a role simultaneously.