| The alpine meadow ecosystem of Qinghai-Tibet Plateau is a region where responds to global change sensitively. Grazing and fertilizing are the most commonly interferential methods in the alpine meadow. Therefore, how biodiversity and ecosystem functioning response to grazing and change of soil resources is an important problem related to production and life of human beings. As functional ecology is developing, scholars research on the relationship between biodiversity and ecosystem functioning, the key point of the research will no longer be confined to species diversity(SD), but shifts to functional diversity(FD). Studying the effects of biodiversity on aboveground net primary productivity(ANPP) plays a important role in measuring ecosystem functioning. So we have conducted the experiment on alpine Kobresia humilis meadow with clipping(unclipping, stubbled 3 cm and 1 cm) and fertilizing(12.75 g·m-2·a-1 urea3.06 g·m-2·a-1 ammonium phosphate) treatments from 2007 to 2013. The differentiation of species composition, SD and ANPP had occurred in communities with different treatment combination, but it is still unknown that whether the relationships of SD—ANPP and FD—ANPP have changed under different treatment combinations. We chose five traits(life cycle, growth form, economic group, cotyledon type, height) which were related to ANPP to calculate FD. We used ANOVA and RMANOVA to study the effects of clipping, fertilizing, year and their interaction on ANPP, SD and FD. Then the regression analysis and ANCOVA were used to examine the relationships of SD—ANPP and FD—ANPP as well as the response of their relation model to clipping and soil resources. The results show that:(1) ANPP was improved by increasing clipping intensity and soil nutrient extremely significantly(p<0.01). The effect extent of fertilizing on ANPP was different in each year, while the effect direction of clipping was varied in each year.(2) There was a higher SD in Kobresia humilis meadow under different treatment combinations. The alternative turnover of species occurred along clipping gradient, so SD did not change significantly(p>0.05). However, SD was improved by clipping significantly in last two years(2012—2013), because clipping released plenty of space and increased spatial heterogeneity by transferring species’competition for light to competition to underground resources and provided suitable condition for immigration of new species. SD did not change significantly in the impact of fertilizing and the interaction of fertilizing and year(p>0.05) which may due to low fertilizing amount.(3) Because the decrement of difference of traits among species was offset by the increment of species evenness after clipping, FD was not significantly different among different clipping intensity(p>0.05). FD was improved by fertilizing significantly(p<0.05) which was related to trait divergence, which was driven by intense competition among species and niche differentiation among coexist species. On the one hand, the unfertilized community and fertilized community were extremely high in proportion of coexist species, and the effect of fertilizing on SD was not significant, so FD did not decrease. On the other hand, the phenomenon of superiority-oppression of competition for light was increased by fertilizing, so FD was higher in fertilizing community.(4) ANPP and SD declined along time, while FD increased along time. Plant was getting short due to long-term clipping, which led to ANPP fluctuant decline year-to-year. However, the fluctuant trend was not related to single precipitation, mean temperature or dryness. The decline of SD along time was mainly attributed to the decline of unclipped community which suffered from moderate grazing for a long time before enclosure. Previous community had higher level of SD and unstable pattern of competition, so the level of SD of the community declined to a balanced state in the process of that the community restored to stability gradually. However, FD increased along time owing to heterogeneity of community space after clipping. This consequence can reflect the time process of the differentiation of trait difference among species and evenness in total community.(5) Under the six kinds of treatment combinations of clipping and fertilizing, the relationships of SD—ANPP and FD—ANPP presented two patterns including linear positive correlation and no correlation mainly depending on clipping. No matter the community was fertilized or not, in the unclipped community, the relationship of SD—ANPP presented linear positive correlation(n=90, p<0.05),while FD showed no correlation with ANPP(n=90, p>0.05). However, in the clipped community, SD showed no correlation with ANPP(n=90, p>0.05), the relationship of SD—ANPP presented linear positive correlation(n=90,p<0.05). Clipping improved FD and ANPP in the same time, which facilitated them to show linear positive correlation.(6) Fertilizing cannot affect the patterns of relationships of SD—ANPP and FD—ANPP, but the slope and intercept of equations of relationships were influenced by fertilizing and clipping. In the unclipped community, the effect of fertilizing on the slope of linear equation of relationship of SD—ANPP was not significant(p>0.05), but fertilizing increased its intercept significantly(p<0.05). In the fertilized and unfertilized communities, clipping increased the slope of linear equation of relationship of FD—ANPP(p<0.05). In the moderate and heavy clipped communities, fertilizing did not affect the slope of linear equation of relationship of FD—ANPP significantly, while fertilizing increased its intercept significantly(p<0.05). The results show that both clipping and fertilizing have a remarkable impact on the relationships of SD—ANPP and FD—ANPP, while clipping plays a leading role.In conclusion, clipping and soil resource have different impacts on SD, FD, ANPP, and the relationships of SD—ANPP and FD—ANPP, and their effects of response also change over time. In this survey, the relational properties of SD—ANPP and FD—ANPP were determined by clipping, and the effect of FD on ANPP would be stronger with the increase of clipping intensity. Meanwhile, fertilizing could increase ANPP of same level of SD of unclipped communities and same level of FD of clipped communities. Therefore, when we research on the relationship between biodiversity and ecosystem functioning, we should take account of not only SD and FD, but also the effects of time scale and abiotic factors. |
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