Effects Of Nutrient Additions On Community Biomass And Diversity Varied Among Different Grassland Ecosystems Of Inner Mongolia

Grasslands represent one of the most widely distributed terrestrial ecosystems on Earth. Biomass and species diversity are important to evaluate ecosystem functions and ecosystem services of grasslands. However, a large area of degradation occurred due to the long-term over-grazing have decreased the grassland productivity and biodiversity. Although effective grassland managements such as nutrient additions, has been proved potentially to increase grassland productivity and ecosystem functions, also exert impact on species diversity. However, it is not clear whether these responses to nutrient addition vary among grassland ecosystems under different climate or environments. To obtain these mainly objects, we established long-term nutrient addition experiments on three grassland ecosystems (meadow steppe, typical steppe and desert steppe) in Inner Mongolia. On the basis of the three-year experiments (2011-2013), we analyzed the impacts of different nutrient additions on above-and belowground biomass, and their species diversity of these grassland ecosystems. The results show that nitrogen leads to the aboveground biomass of grassland in Inner Mongolia increased by27%～53.3%, an average increase of37.8%, and the higher N gradient, the larger biomass. Belowground biomass decreased slightly in meadow steppe and desert grassland by nitrogen addition, but promotes the accumulation of belowground biomass of typical steppe. Biomass responds to P addition less deeply than N addition. By contrast, belowground biomass has a less response to fertilization than aboveground biomass. Furthermore, the response of biomass to nutrient addition varied among three grassland ecosystems. In arid desert steppe, community biomass is more sensitive to N limitation than the typical steppe and meadow steppe. Likewise, N addition reduced belowground biomass and R:S ratio in meadow steppe and desert steppe, whereas promoted that values in typical steppe. In contrast, nutrient additions have relatively less and insignificant impacts on the root distribution of temperate grasses. It is notably, the response of the above-mentioned responses to nutrient addition varied among years. Our observations indicate that nutrient addition would have different effects on community biomass regulated by different environmental conditions. Nutrients additions also have different effects on the community composition and structure, as illustrated by reduced the Shannon-Wiener diversity index and Pielou index. Likewise, the above-mentions effects also differed among three grassland communities and among years. Our results suggest that it necessary to consider the changed response of different grassland ecosystems to nutrient addition in the carbon cycle models budget and grassland management.