Study On Nitrogen Content And Its Response To Drought And Salinity Stress At Aegiceras Corniculatum Wetland

Due to human activities and global climate changes,many of mangrove forests have experienced significant changes around the world.Primary productivity can be directly affected by nitrogen in wetland ecosystem,so study on nitrogen content and its morphology of migration and transformation process in wetland can effectively reflect the change of wetland environment.This paper has chosen Aegiceras corniculatum wetland as the research object.On one side,we have researched seasonal variation of nitrogen content and their relationship with the soil physical and chemical properties of the wetland in the natural state.On the other hand,we have researched nitrogen content of each form and their response mechanism when subjected to drought and salinity stress in the wetland through the simulation experiment,the main conclusions are as follows:(1)A.corniculatum can change its soil basic physicochemical properties to some degree.The soil nitrogen content in autumn and winter was higher than that in spring and summer,and content of nitrate nitrogen in spring and summer is lower while the ammonium nitrogen is lower in autumn and winter.The rates of nitrification and denitrification were 24.72 and 37.36 mol/(L·h),respectively.The total nitrogen of covered water of soil within the wetland was higher than outside of the wetland in spring,but slightly lower in the rest of the season.The content of nitrite nitrogen within the wetland is significantly higher than outside of the wetland,while content of nitrate nitrogen and ammonia nitrogen were higher in spring and summer.The total nitrogen content of each organ showed that the root < stem < leaf,and the total nitrogen content in roots and leaves was higher in spring and summer.(2)The basic physical characteristics of soil can be changed by drought and salt stress,and obviously when treated by coupled stresses.The growth of seedlings were suppressed,but the underground part of inhibitory effect was not significant.Except treatments of salinity,the rest of all have raised the N2 O emission flux.(3)Drought stress can significantly reduce the root and leaf nitrogen content,A.corniculatum tend to assigned more absorbed nitrogen to leaf instead of root.Under drought stress,soil nitrate nitrogen content increased significantly but ammonium nitrogen decreased significantly.Content of total nitrogen,ammonia nitrogen,nitrite nitrogen in water decreased significantly under highly drought stress.Salt stress reduced leaf nitrogen content,seedlings tend to assigned more absorbed nitrogen to roots and stem,and significantly increased stem nitrogen content treated by 30‰ salinity.Significantly increased soil total nitrogen,but instead,reduced ammonium nitrogen content.Nitrate nitrogen content significantly was reduced by 20‰ salinity treatment while increased significantly by 30‰ salinity treatment.The content of total nitrogen,ammonia nitrogen and nitrate in water dropped significantly.(4)Drought-20‰ salinity coupled stress significantly decreased the nitrogen content and 15 N distribution rate of roots and leaves,but no significant effect on stem nitrogen content.The content of soil nitrate nitrogen was increased significantly,while ammonium nitrogen increased significantly in moderate drought,but decreased significantly at high drought.The ammonia nitrogen content in water decreased significantly,while the other 3 kinds of nitrogen increased significantly in moderate drought,but decreased in high drought.Under drought-30‰ salinity coupled stress,the nitrogen content of roots and stems were decreased significantly while the rate of 15 N distribution of stem increased,but the leaf nitrogen content and 15 N distribution rate was decreased.The content of nitrate nitrogen in soil was significantly increased,and the content of total nitrogen and ammonium nitrogen decreased significantly at high drought.The total nitrogen and nitrate in water decreased significantly,while the nitrite content was not significantly increased.The content of ammonia nitrogen in water in moderate drought significantly reduced but increased in highly drought.