Maintaince Mechanism Of Understory Herbaceous Species Diversity In Taibai Mountain

Community assembly is the focus of community ecology study, and species diversity is the useful tools for studying community assembly process along environmental gradient. Understory herbaceous species is an important part of forest community, therefore it is necessary to study assembly mechanism of understory herbaceous community for understanding the assembly mechanism of forest community. Recently, more researchers tend to using plant functional traits to evaluate assembly patterns of plant community. In our study, we investigated the species composition and functional traits of understory herbaceous community in main forest types of Taibai Mountain, and analyzed the assembly pattern based on functional trait structure and diversity index. The results obtained is useful to understand the assembly process of forest community in Taibai Mountain.In this study, we established 41 plots randomly along elevation of 1113m-3513m range. We recorded the species identification and environment information per plot, and obtained soil sample and every plant species specimen in every plot. We measured functional traits of herbaceous species and analyzed the physicochemical property of soil per plot. We calculated the important value to confirm the importance of herbaceous species. Also, we ran a CCA to ascertain the dominated factor influencing the species composition. We also confirmed the factors influencing herbaceous species functional traits by using RDA and variance decomposition. Linear fitting was used to highlight the relationship of diversity and functional traits of forest community and understory herbaceous community versus altitude gradient. In addition, we investigated the similarities and differences of species composition and diversity pattern between community and herbaceous species by correlation analysis. Meanwhile, we constructed a null model to test assembly process of understory herbaceous community along main environment gradient. The conclusions as follow:(1) Herbaceous layer species account for a large percentage of community richness. The species composition and diversity pattern of understory herbaceous community was similar with forest community in total, while the dissimilarity was found in some details, suggesting that understory herbaceous community should be focused in studying the assembly process of forest communities. The species composition was affected by altitude, but scale-dependent. The change of species composition along the altitude is significant in wide altitudinal range, but not in a narrow altitudinal range.(2) Understory herbaceous species contributed a lot to species diversity of forest community in Taibai Mountain. Altitude primarily affected the diversity of herbaceous species. Our results showed a rising at first and then down along altitude gradient for community species. However, the decrease of herbaceous diversity along the altitude was not found in correlation analysis with slope and WCD.(3) Altitude played an important role in functional traits variation. With altitude rising, SLA, LA and Hmax declined but LDMC, LCC and LNC rised.(4) In high elevations, the harsh condition led to convergence on trait structure. In middle elevation zone, herbaceous species trait structure showed over-distributed because of the suitable environment condition, suggesting similarity limited in these plots. In low elevation zone, there was a disperse tendency in trait structure of herbaceous species, while showed converged in few disturbed plots. It was a deterministic process for herbaceous community assembly in forest communities of Taibai Mountain, supporting the niche-hypothesis.