Effects Of Resource Additions On Species Diversity Of Alpine Meadow On Qinghai-Tibetan Plateau

The earth is undergoing ecological and environmental changes because of human-driven land use, eutrophication, so the accelerating loss of biodiversity has become a primary concern.Maintenance mechanism of plant community species diversity has traditionally been viewed as a historical dichotomy of individualistic versus organismal classifications. In essence, either a random collection of individuals or organismal entities emphasized different opinions for maintenance mechanism of plant community species diversity and community structure. In the late debate, competition and niche differentiation had been viewed as dominant factors influencing community structure in ecological research. Classical ecological theory predicts that it cause competing coexistence only when the number of species was less than or equal to the number of limiting resources. Modern community ecologist extend this theory and show that a large amounts of species can coexist on several limiting resources if there is spatial-temporal heterogeneity and interspecific tradeoff in utilization strategy of limiting resources. Meanwhile, niche dimension-diversity hypothesis predicts that the number of limiting resource is also a key factor influencing species diversity. Many field experiments have tested the theory and confirmed that, wherever in freshwater or terrestrial ecosystems, resource addition lead to increase in aboveground primary productivity (ANPP) and decrease in species diversity. Based on the hypothesis, we choices specific limiting resources, such as soil nutrients (N, P, K) and water to explore the correlation between resource addition and species diversity in plant community. Our major question as following: 1) whether plant species richness was related to the number of limiting resources? 2) whether the different limiting resources had similar effects on species richness? 3) whether the underlying mechanism linking species richness loss to the addition oflimiting resources was an increased ANPP?Resource additions (N, P, K, water) were conducted in an alpine meadow of the Qinghai-Tibetan Plateau for two years. Plant aboveground biomass, species composition, mean plant height, and light availability were measured in each plot. We tested the responses of species richness and ANPP to resource additions using a general linear model. Analysis of variance (ANOVA) was used to examine the significance of explanatory terms. Relative light intensity (light intensity above canopy/light intensity under canopy) was calculated and log-transformed to obtain normally distributed residuals. In addition, we also used the Gini coefficient of plant height as a measure or size inequality among plant functional groups following the number of limiting resources.The results as following:1) There is a linear correlation between the number of limiting resource and species richness (negative) or ANPP (positive), that is, species richness decrease and ANPP increase with the number of added limiting resources.2) Effects of any treatments with N (N, NP, NPK) on species richness were inerasably decreasing trend, and loss of species number has focused largely on forbs species. Other non-N resource addition treatments have no importantly produce effect on species richness. In addition, any treatments with N resource lead to an increase in ANPP:N addition increased the biomass of grasses on average by 250% and that of sedges by 26.4%, but it decreased the biomass of legumes on average by 28.5% and that of forbs by 30.2%. Adding N and P together produced a stronger response than N and P additions alone. Additions of P and K, both alone or in combination, had no significant effect on ANPP. Water addition significantly increased ANPP compared with control plots.3) There is a negative linear correlation between ANPP and light availability. The Gini coefficient of plant functional group height increased with increasing number of added limiting resource.From this study, we have drawn the following conclusions:1) Our experimental results support the niche dimension-diversity hypothesis, i.e. the decrease of niche dimension due to the addition of limiting resources is a reasonable explanation for decreased species richness.2) Effects of N, P, K or water additions on species richness and ANPP were not equivalent. Nitrogen is most primarily limiting resource for species richness and ANPP. There are additive effects among N adding other limiting resources for plant species diversity. Under this condition, all treatments including nitrogen with the increasing number of added limiting resource cause increase in ANPP and decrease in species richness, and NPK treatment (eutrophication model) produce most largely negative effect for species diversity (the most reduction of species richness).3) Resource additions lead to increase in ANPP and plant species become light-limited, so resource competition shift to light competition. The shift cause eventually species competition exclusion. So we predict that light competition hypothesis have reasonable explaination for plant species diversity loss.