The Relative Contribution Of Species Diversity And Functional Group Diversity To Above-ground Net Primary Productivity

Influenced by natural factors and human activities, global biodiversity is rapidly losing, so the relationship between biodiversity and ecosystem function?BEF? has became a central issue in the research of ecosystem. BEF essentially refers to the biological diversity of the ecosystem function effect, aboveground net primary productivity?ANPP? is a comprehensive index of ecosystem function, and it is an effective way to study BEF. Since 1970s, the world has carried out a large number of studies on the relationship between community species diversity?SD? and aboveground net primary productivity, but the results had not been consistent. Many studies suggest that the ecosystem function was mainly driven by the key function of plant community group or the main function type composition and its role should be greater than the effects of species richness on ecosystem function. Different species has different characteristics in the community, and their functional properties and responses to disturbance were also different. The functional groups which were composed of the same or similar species has different effects on the ecosystem function. We hypothesized that as biodiversity composition and functional group diversity?FGD? on primary productivity also has an impact, and species diversity should be complementary, but its contribution may greater than species diversity of contribution to primary productivity. So we used clipping?set of clipping, unclipping, moderate clipping, heavy clipping 3 levels, using NC, MC and HC representation? and fertilization ?with fertilizer and unfertilizer 2 levels, using NF and F representation? control experiment from 2007 to 2013 in Alpine Kobresia Meadow?Kobresia humilis?. Based on the life cycle of the species, economic groups and the production performance of the plant functional groups were divided into "G1" and "G2" function group, respectively with the most commonly used species richness index ?R?(species richness index of community species, functional groups G1 and G2 were respectively used in RS, R_G1 and R_G2), Simpson dominance index ?D?(Simpson dominance index of community species, functional groups G1 and G2 were respectively used in DS, D_G1 and D_G2) and Shannon-Wiener diversity index ?H'?(Shannon-Wiener diversity index of community species, functional groups G1 and G2 were respectively used in H'S, H'_G1 and H'_G2) group diversity quantification of species diversity and functional group diversity, on the one hand, we researched the effects of clipping, fertilizing, year and their interaction on species diversity, functional group diversity and productivity. On the other hand, we aslo researched the effects of clipping and fertilization on relationship between species diversity and productivity and relationship between functional group diversity and productivity. In addition, we compared the relative contribution of species diversity and functional diversity to productivity. The results were as follows:?1? This study showed that clipping had no significant effect on R_s and H'_s?p>0.05?, with the increasing of clipping intensities, the Ds increased significantly?p<0.05?, but after fertilization, R_s, H'_s and Ds reduced significantly?p<0.05?. So clipping mainly reduced community dominance and increased species diversity, but it had no effect on Hs; Fertilization increased community dominance and decreased 3 diversity indices. Therefore, clipping did not necessarily increase each of diversity index, but fertilization had the reducing effect on species diversity.?2? Clipping had significant effect on the functional group richness?R??p<0.01?, with the clipping intensity increased, R_G1 decreased significantly, and it had no significant effect on the other two functional group diversity index?p>0.05?, On the contrary, fertilization significantly reduced the D_G1, D_G2, H'_G1 and H'_G2?p<0.01?, but there was no significant effect on the functional group richness?R??p>0.05?. Clipping significantly reduced functional group richness but fertilization significantly increased functional group dominance, so the different diversity index showed different results after the same interference, which shows that studying the structure of grassland community under various disturbance factors, it is necessary to adopt different functional group diversity index, from different sides more accurately reveal the change of the functional group of the community.?3? Clipping and fertilization treatment can significantly increased the group aboveground net primary productivity?p<0.01?, and fertilization increased more obvious. In the community without the interference of the implementation process, the net primary productivity decreased year by year, but in the clipping and fertilization community productivity, with the year performance fluctuations, indicating that moderate grazing and soil resources can prevent community productivity continued to decline, and keeping productivity at a certain level.?4? From the results of the Pearson correlation analysis of species diversity index and community productivity:? in the clipping and fertilization composite gradient, only Ds-ANPP significant negative correlation,RS-ANPP and H'S-ANPP had no significant correlation.? In unfertilization, RS-ANPP, DS-ANPP and H'S-ANPP had positive correlation, negative correlation and uncorrelation of 3 modes ? In only fertilizer application,the three diversity index and ANPP were not correlated. If clipping and fertilizing at the same time, ANPP only with Ds was negative correlation. In our study, The relationship between species diversity and productivity had three modes?positive correlation, negative correlation and uncorrelation?, so effectively predict ANPP variation of species diversity index which was related to the disturbance factor, the disturbance intensity and the diversity index. There were different relationships between different species diversity, under different disturbance, the pattern was also different, thus the relationship between species diversity and productivity was not determined, their relationship was influenced by the choice of species diversity index and interference.?5? Pearson correlation analysis showed that:under the six kinds of treatment combinations of clipping and fertilizing, In the Gl function group, the relationships of R_G1-ANPP significantly negatively correlated or not correlated; the relationships of D_G1-ANPP and H'_G1-ANPP were significantly positively correlated or not correlation; For G2 function group, in the gradient composite?CG community?, the relationships of, D_G2-ANPP and H'_G2-ANPP was significant negative correlation; In clipping but not fertilized community, the relationships of D_G2-ANPP and H'_G2-ANPP were significant positive correlation; In heavy clipping and fertilization community, R_G2, D_G2 and H'_G2 were significantly negatively correlated with ANPP. The relationship between RG and ANPP were negatively correlated; disturbance intensity increase, the relationship between D_G1, H'_G1 and ANPP from positive correlation to unrelated; the relationship between D_G2,H'_G2 and ANPP from was positively correlated to negative correlation. It showed that the single function diversity index can effectively predict the ability of productivity to change with time and the interference was limited; Functional groups were divided in different ways, the relationship between functional group diversity and productivity was also different.?6? Multiple stepwise regression analysis showed that:In the composite treatment community, The largest contribution to ANPP was R_G1, followed by Ds, the lower contribution was R_s.Without fertilization, in the NC-NF community, only D_G2 was selected, and its contribution to ANPP was 39.7%;In the MC-NF community, R_s and H'_G1 was selected, but the contribution of H'_G1 to more than RS; In the HC-NF community, R_G1 and R_G2 were selected as the optimal model. After fertilization, in the NC-F community, H'S and D_G1 was selected, the relative contribution of D_G1 was greater than H'S. Aboveground net primary productivity was decided by the species diversity and functional group diversity together, but species diversity and functional group diversity on productivity with whether under that kind of treatment and diversity index, the functional group diversity contributions were greater than species diversity, so ecological system function was more determined by functional attributes, so the ecosystem function was determined by the functional attributes.In summary, clipping and fertilization had different impacts on SD, FGD, ANPP, and the relationships of SD-ANPP and FGD-ANPP. Net primary productivity of alpine meadow community was jointly decided by the species diversity and functional group diversity, clipping and fertilizing disturbance increased the species diversity and functional group diversity on net primary productivity contribution, but did not affect functional group diversity on net primary productivity with greater than species diversity pattern, but the contribution of functional group diversity to aboveground net primary productivity was still greater than that of species diversity. So the relationship between diversity and ecosystem can not only consider the influence of single index, but should consider the influence of functional group diversity and species diversity. In addition, different diversity indices had different responses to the same disturbance, thus the use of multi diversity index can more fully and truly reflect species diversity and functional group diversity on the interference of the response.