The Seasonal Changes Of Soil Available N,P Contents And Their Forms Under Different Water Gradients In The Typical Wetland Of Poyang Lake

Wetland is the most bio-diversity and ecological function ecosystem in the nature. Water is the basic ecological factor and the important controlling factor in wetland ecosystem. The moisture change not only has a direct impact on vegetation type but also is bound to affect the transformation and recycling of the wetland elements. Soil nitrogen (N) and phosphorus (P) are the most important nutritional elements in plant growth, and their availability has a significant impact on plant growth, while N, P are also the main elements which can make permanent flooded wetlands such as rivers, lakes and so on occur eutrophication. In recent years, due to climate change, human activities and other reasons, Nanjishan Natural Reserve in the Poyang Lake is always short of water every year, and there has been a phenomenon for many years that the water level dropped. The seasonal change and correlation of soil available N, P content, their forms, and soil microbial biomass-C, N, various enzyme activities in three typical vegetation community which include Cynodon Grassland, Triarrhena Beach Wetland and Carex Beach Wetland which are in different water gradients in Nanjishan Reserve of the Poyang lake were studied. The objective is to reveal the influence of water gradient on wetland available N, P content and their forms, enhance the understanding of the influence of water level decrease on wetland soil available N, P, and provide scientific data for better evaluating the influence of water level decrease on Nanjishan wetland ecosystem, guiding the management in Nanjishan wetland, and promoting its sustainable development. The main results are as follows:(1) Water gradient and season have a extremely significant impact on the content of soil available N, P and their various forms in Nanjishan wetland. Generally speaking, the content in Triarrhena and Carex Beach Wetland is more than in Cynodon Grassland, and the seasonal changing rules are all different.(2) The main form of soil available N under three different water gradients in Nanjishan wetland is NH4+-N.(3) The main forms of soil available P under three different water gradients in Nanjishan wetland are all residual P, HC1-P and NaOH-P, accounting for more than 92% of total P.(4) Soil moisture has significant impact on the content of soil available N, P in Nanjishan wetland. By contrast, soil microbial biomass C, N and sucrase, urease, acid phosphatase activities has no significant impact on available N and P content in Nanjishan wetlandIn short, soil water gradient and moisture have a significant impact on soil available N, P in Nanjishan wetland. Water is the main factor which can affect the availability of wetland soil N and P.