| Biodiversity not only maintains the balance of nature,but also provides drugs,food and other resources for human beings,which are material basis for human survival and development.Nowadays,biodiversity was seriously lost,and it was urgent to protect biodiversity.Exploring the mechanism of community assembly was very important to explain the coexistence of community species and the maintenance mechanisms of biodiversity.Community assembly has always been one of the core issues in the study of community ecology.Taking alpine meadow as the research object,we measured the leaf functional traits?specific leaf area,leaf dry matter content,leaf relative water content,leaf carbon content,leaf kalium content,leaf phosphoru content,leaf nitrogen content,chlorophyll content?and soil environmental factors?soil water content,soil organic carbon,soil available nitrogen,soil available phosphorus,soil total phosphorus,soil total phosphorus,soil total nitrogen:soil total phosphorus,soil acility and alkalinity?in different slopes.We selected five slopes'plotsand we tested the relatedness indices NTI and NRI.Then constructed the plant community phylogenetic tree which was based on the Angiosperm Phylogeny Group?APG?III.This paper attempted to explore the community assembly mechanism of alpine meadow along slope gradient by combining the method of community phylogeny with the leaf functional traits of plant.The results as follows:?1?The physicochemical properties of soil had significant difference along different slope aspects.The variation range of soil moisture content on the northern and southern slopes was 0.38g·g-10.16g·g-1.Soil water content decreased from the northern slope to the southern slope.The change trend of soil total nitrogen,soil organic carbon and soil nitrogen and phosphorus ratio was the same.With changed in the slope aspect from south to north,the value of soil total nitrogen,soil organic carbon and soil nitrogen and phosphorus ratio first decreased,reduced the minimum value in the east slope,and then rose again.The overall change trend was v-shaped.There was no significant difference of soil available phosphorus content among different slopes,but soil available phosphorus content of northern slope(0.135g·kg-1)was slightly higher than the southern slope(0.125 g·kg-1).The pH of the soil varies slightly on five slopes,but the soil of the southern slope is more alkaline than that the northern slope.The contents of soil available nitrogen and soil total phosphorus in the northern slope were higher than other slopes,and the contents in the eastern and southeast slope were the lowest.?2?The slope gradient had a significant effect on the plant leaves functional traits.With changes in the slope aspect from south to north,the value of leaf moisture content and specific leaf area were decreased.The relative chlorophyll content increased successively?from north to south?in the five slopes,and the change rule of SPAD and SLA LWC was opposite.The content of leaf dry matter decreased successively from south to north,except that the value of the northern slope was slightly higher than the northeast slope.The leaves nitrogen content and leaves carbon content did not have significantly difference in fives slope.The phosphorus and potassium contents of leaves were different along the five slopes,and there were no obvious change rules.But on the whole,the leaves phosphorus and potassium content in northeast slope was the highest and that in the southeast slope was the lowest.The dominant functional groups of each slope quadrate community changed with the different slope.The sample communities were dominated by Primulaceae and Rosaceae in the northern slope aspect.The northeast slope was dominated by Cyperaceae,and the east slope was dominated by Compositae.The southeast slope and the southern slope were dominated by Poaceae.?3?The phylogenetic diversity index and phylogenetic structure of the community showed same regularity with the slope change from north to south.Phylogenetic diversity index decreased gradually.The degree of clustered was decrease,which community phylogenetic structure shifted from over-dispersion to clustered.The genetic index values of the northern slope were greater than zero?NRI=0.6432,NTI=0.2515?,thus the phylogenetic structure was clustered.The phylogenetic structure of the southern,southeast and eastern slopes was over-dispersion.In the northern slope,the nearest relatedness index indicated phylogenetic clustered,while the net taxon index close to zero but greater than zero indicated phylogenetic random dispersion or clustered.?4?Combined environmental factors with leaf character and phylogenetic structure,we found that environmental factors such as soil nutrient and water content on slope gradient had significant impact on plants on the south slope and the southeast slope,followed by the east and northeast slopes.And environmental factors had the least impact on plant growth on the northern slope.Phylogenetic structure clustered,in that interspecific competition was the main driving forces of community assembly in the northern slope.The phylogenetic structure in the south,southeast and east slopes were over-dispersion,in that the habitat filtration were the driving factor of the community assembly.In the northern slope,the nearest relatedness index indicated phylogenetic clustered,while the net taxon index indicated phylogenetic random dispersion or clustered.This means the northeast slope's phylogenetic index may be the result of several mechanisms working together and the process of community assembly was more complicated. |
PDF Full Text Request