Alpine Kobresia Humilis Meadow Species Diversity, Functional Diversity And Primary Productivity Of The Relationship

In recent years, plant functional diversity has been became a new research focus. Whether species diversity (SD) in natural ecosystem covaries with funcitional diversity(FD) and consequently affects the productivity is still an open question. In this paper, Rao coefficient was used to calculate functional diversity quantitatively, this is a new exploration of the community diversity. A field grazing experiment was conducted on an alpine Kobresia humilis meadow to study the effects of SD and FD on primary productivity of the ecosystem. Four habitats with different grazing intensities and soil nutrient availability, i.e., pen pasture, with heavy grazing intensity and highest nutrient availability, pass pasture with moderate grazing intensity and moderate nutrient availability, artificial pasture with light-moderate grazing intensity and lower nutrient availability, ungrazed pasture with null grazing intensity and lowest nutrient availability. At the same time, we analyzed the 6 plant traits (plant height, above ground weight (AGW),specific leaf area (SLA), leaf size (LS) , leaf dry weight (LDW), specific leaf weight (SLW) )of 18 dominating species in the habitats to quantitative calculation FD, which provided a theoretical basis for rational use of meadow. The main results showed as follow:(1) Among the test habitas, pass pasture had the hightest SD, which accorded with intermediate disturbance hypothesis (IDH). IDH still conincide in the case of complex conditions in the area.(2) There are significant correlationships among plant traits( P<0.01 ). Plant height was significantly positive correlation with specific leaf area (SLA) (P<0.01). The same to leaf size (LS) and leaf dry weight (LDW). SLA was significantly reduced with the grazing intensity in pass pasture, artificial pasture and ungrazed pasture. This shows that SLA was negatively correlated to grazing intensity (P<0.01). The leaf size, leaf dry weight, specific leaf area and specific leaf weight were high in ungrazed pasture with low nutrient availability. This shows that the grazing disturbance has an obviously impact on plant leaves traits. SLA was the highest in pen pasture with the greatest grazing intensity, because the rich nutrient conditions could reduce the grazing damage to plants. This indicates that the plants traits are affected by grazing intensity and soil nutrient together. Rich nutrient soil conditions reduced the adverse effects of grazing disturbance.(3) For both single trait and combinated traits, FD were significant difference among habitats (P<0.001). FD_H, FD_AGW and FD_LDW were higher than FD_SLA, FD_SLW and FD_LDW. FD for combinated traits was the mean of the FD for the six traits, which respected community FD totally .FD for plant height and FD for leaf traits had slightly different because of differences in traits, but the change of FD in habitats reflected the basically unanimous trend: pen pasture > artificial pasture> pass pasture> ungrazed pasture. It showed that pen pasture had the highest interspecific difference on plant height, above ground weightand leaf dry weight ,while ungrazed pasture had the lowest interspecific difference.(4) Primary productivity determinated in June and August were significant differences (P<0.01 ).Primary productivity was no significant differences between at pen pasture and pass pasture (P>0.05) , but higher than artificial pasture and ungraded pasture, there was no significant difference between the latters. Pen pasture had the highest primary productivity; this is because pen pasture had rich nutrient conditions.(5) Pen pasture and artificial pasture had low SD but the highest FD, while pass pasture had the higher SD and FD. Ungrazed pasture had high SD but the lowest FD. There was a positive relationship between SD and primary productivity but a negative relationship between FD and primary productivity, suggesting that FD didn't covary with SD, both SD and FD could affect primary productivity independently.(6) The PCA of SD and FD shows that the contribution rate of the first principal component (63.78%) was much larger than the second principal component's (27.99%). The first principal component mainly responsed the information of FD, and the second principal mainly responsed the SD's. This shows that the roles of SD and FD in community were different; FD may have a greater influence upon ecosystem.(7) The CCA of SD, FD and soil factors showed that the first axis of CCA basically indicated the diversification of community diversity with soil factors. Nitrate nitrogen,total phosphorus and phosphorus pentoxide wre principal factors which depended on the dynamic rule of diversity, while the effected of pH on community is insignificant. There was a positive relationship between FD and nitrate nitrogen, total phosphorus and phosphorus pentoxide but a negative relationship between SD and nitrate nitrogen, total phosphorus and phosphorus pentoxide.This shows that the effect of soil factors on SD and FD is different,which may be one of a reason for inconsistent variety of SD and FD. Rich nutrient communities had low SD but high FD.These results suggested that FD didn't covary with SD, SD is not necessarily equivalent to FD, FD may have a greater role to ecosystem. FD and SD may independent of each other to a certain extent. The mechanism based on the differences between multi-species co-existence of the community can not explain the differentiation FD of species. In other words, SD and FD are two different issues of community characteristics. Grassland ecosystem is a highly heterogeneous system that composed by the different use pattern of grazing and reclamation and small communities with the changing conditions of habitat resources. The relationships between SD, FD and primary productivity are complexity in the ecosystem. A variety of factors inhibiting and promoting affected the community's structure and functional properties in an integrative way. Plant height and leaf traits could well reflect the community traits varieties of alpine meadow. This study showed that it's significant to study FD which reveal the mechanism of ecosystem function.