Effects Of Warming And Nitrogen Deposition On Soil Nutrient Status In Songnen Meadow Steppe

Songnen Meadow Steppe, which is in northeast China, is increasingly affectedby global warming and incremental increases in atmospheric nitrogen deposition.However, the responses of nitrogen (N) and phosphorus (P) in steppe soil, and of thecoupling mechanism between them, to the dual effects of global warming and Ndeposition are still unknown. In this study, the effects of simulated atmosphericwarming and N deposition on N and P in Songnen steppe soil, on the couplingbetween N and P, as well as on the soil microbial biomass were examined under insitu conditions from2007to2010. Infrared heaters were used to elevate soiltemperature by approximately1.7°C since2006. N additions were treated once a yearwith aqueous ammonium nitrate at a rate of10g m–2a–1. During the four-year study:(1) Addition of N increased the amount of total N, and available N, as well as therate of N mineralization in the soil. Moreover, the amounts of total P and available Pin the soil were considerably reduced. Soil total N, available N, total P, available Pand NH4+-N content were not significantly affected by warming, which means thatwarming did not significantly impact soil important nutrient in Songnen MeadowSteppe.(2) The N: P ratio increases with N addition, and the increase in the amount of N,as well as the decrease in the amount of P, have different effects on N and P. Therefore,the coupling mechanism between soil N and P is reduced, as reflected by thesignificant reduction in the liner relationship between total N and available P as wellas between available N and available P in N addition compare with control. With thegrowth of China’s industrialization, N deposition continues to increase. The studyarea of Songnen Meadow Steppe, and northeast China in general, are characterized bywidespread distribution of saline alkali soil. Therefore, the finding of increased Plimitation in the soil of Songnen Meadow Steppe has major implications forecosystems in northeast China. Reasonable regulation and management of meadowsoil nutrients will be of great importance in increasing soil productivity and promotingsustainable use of grassland ecosystems. (3) Soil microbial biomass N was significantly increased by N addition, whichmade the soil microbial biomass P content significantly decreased. Interaction ofwarming and N addition significantly increased the content of soil microbial biomassC, however, warming did not significantly influence it. N addition significantlyincreased soil microbial biomass C: P ratio, which was also suggested that the contentof soil microbial biomass P was lacking in Songnen meadow steppe, soil nutrientwere turning into P limitation. There were better correlated between soil microbialbiomass and soil important nutrient, especially the correlation is more significantwhen N addition. Therefore the soil microbial biomass can be used as biologicalindicators, which could evaluate the long-term changes in soil quality.Overall, this research provides a theoretical basis for understanding the influenceof ongoing trends related to global changes on soil nutrients in Songnen MeadowSteppe, and it is relevant to determining methods to facilitate the recovery ofgrassland ecosystems and protect the environment as global changes occur.