Effects Of Water And Nitrogen And Litter Addition On Leymus Chinensis Grassland

Human activities have been altering the global climate since the industrial revolution, such as changes in precipitation regimes and nitrogen deposition. Precipitation is predicted to increase at the mid-latitude regions over this century. The increased precipitation and nitrogen deposition will increase litter input to the soil. Plant litter is a key component of grassland and plays a major role in terrestrial ecosystem processes. It may feed back to the grassland ecosystem responses to climate change. In order to explore the mechanisms of water, nitrogen and litter addition on Leymus chinensis grassland ecosystems, and the mediate effects of litter addition on grassland responds to climate change, we conducted a 3-year field experiment to investigate the effects of water, nitrogen and litter addition on 1) above and belowground productivity, resource allocation, and resource use efficiency,2) species diversity 3) the microbial biomass and microbial diversity, the soil organic carbon and soil total nitrogen 4) nutrient resorption of the dominant species, Leymus chinensis, in Inner Mongolia.Our results showed that1) Water, nitrogen, and litter addition increased aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP), by influncing soil moisture, soil temperature, soil inorganic nitrogen and soil bulk density. Besides, litter addition increased BNPP responses to water addition. These litter addition effects could be attributed to the influence of litter on soil moisture and soil nitrogen availability, ultimately increasing belowground water use efficiency (WUEBNPP). Water addition increased the stem:leaf ratio, and reduced specific leaf area of Leymus chinensis.2) Water, nitrogen and litter addition increased the height of grasses, and reduced the photosynthetic active radiation (PAR), and the abundance of forbs, leading to the decline of species diversity. Besides, at the low quanity of litter, litter addition increased the species richness, while, at the high quanity of litter, litter addition reduced the species diversity, by inhibiting seed germination and establishment.3) Water addition increased soil organic carbon and soil total nitrogen. Litter addition had no effects on soil organic carbon alone, but increased soil organic carbon under water addition conditions. Nitrogen addition had no effects on them.4) Due to the "delusion effects", water availability modulated N and P resorption responses to inputs of N and litter. N inputs significantly decreased N resorption in leaves, reflecting in low N resorption efficiency and high proficiency in response to N inputs, whereas, increased P resorption only under ambient water conditions. Although there were no clear influence of litter and water addition on N and P resorption efficiencies in leaves, or none of treatments on N and P resorption efficiency in stem, we actually found significant changes of N and P proficiencies, mainly associated with alteration in N and P concentrations in green organ in response to treatments, respectively.In conclusion, our results showed that water, nitrogen and litter addition significantly affectd Leymus chinensis grassland ecosystems. Besides, litter had an important mediate effect on Leymus chinensis grassland ecosystems responds to climate change.