The Effect Of Flooding Duration On Soil Nitrogen Mineralization Rate In Littoral Wetland Of Poyang Lake During Non-flooding Period

Hydrological pattern is the main influencing factor of wetland ecosystem.Under the influence of global climate change and human activities,the global wetland hydrological pattern is changing significantly,and affects the process of wetland soil nitrogen mineralization.However,there are few studies on the effect of flooding duration on soil nitrogen mineralization and its regulation mechanism,especially in the dry season.This study was carried out in Poyang lake wetland,and five transects were set along the natural flooding duration gradient: Artemisia selengensis community,Phalaris arundinacea community,Carex cinerascens community,Heleocharis valleculosa community and bare flat.Through the field in-situ nitrogen mineralization experiment and the field single factor control experiment studied how the flood duration affected the soil nitrogen mineralization of the wetland by affecting the soil physical and chemical properties,soil enzyme activity and microbial functional gene abundance.The main research results are as follows:1)The increase of flooding duration significantly increased the rate of soil net ammonification and mineralization,decreased the rate of net nitrification.The effect of flooding duration on soil nitrogen mineralization was affected by different months.In January and March,the increase in flooding duration significantly increased the rate of net ammonification and mineralization,and decreased the rate of net nitrification,while in February,the rate of soil net ammonification,nitrification and mineralization were not significantly affected;2)The increase of flooding duration significantly increased soil moisture and p H,but the impact of flooding duration on soil temperature depended on different months.The duration of flooding may affect soil nitrogen mineralization rate mainly by affecting physical and chemical properties such as soil moisture,p H,and temperature,while microbial gene abundance and soil enzyme activity pathways have little contribution to soil nitrogen mineralization rate;3)The increase of soil moisture significantly increased the rate of net ammonification and mineralization,but had no significant effect on the rate of net nitrification.The effect of soil moisture on soil nitrogen mineralization rate was affected by different months.In January and February,the increase of soil moisture significantly increased soil net ammonification,nitrification,and mineralization rates,while in March,the rate of soil net ammonification,nitrification and mineralization were not significantly affected.The increase of soil moisture may increase soil nitrogen mineralization rates by increasing soil p H,decreasing soil organic carbon content,increasing protease activity and abundance of neutral metalloprotease genes;4)The relationship between soil temperature and net ammonification rate,nitrification rate and mineralization rate is a ∩-shaped parabola.The relationship between soil temperature with soil p H is a U-shaped curve,which has no significant effect on other soil physical and chemical properties.Soil temperature mainly affects the rate of soil nitrogen mineralization by affecting soil p H;In conclusion,the increase of flooding duration will promote the soil nitrogen mineralization of wetland in dry season by increasing soil moisture,affecting soil temperature and p H,enzyme activity,microbial community composition and other ways,and the influence mechanism is different in different months.As a large number of wetlands around the world are facing the problem of nitrogen eutrophication,the study is of great significance to understand the wetland soil nitrogen cycle and its response to the change of hydrological pattern,and then promote wetland protection and management.