Effects Of Nitrogen Deposition On Soil Organic Carbon In Shrub Grass Tundra Of Changbai Mountain

The cold region represented by tundra zone is the key and sensitive area for the change of soil organic carbon pool.Under the background of global climate change,the vegetation of tundra has changed significantly,which will cause the change of soil organic carbon pool.At the same time,the tundra ecosystem is obviously restricted by nitrogen,once the nitrogen increases,not only directly affects the change of soil organic carbon;In addition,by changing vegetation,the quantity and quality of exogenous carbon will be changed,which will affect soil carbon input and indirectly affect soil organic carbon change.In recent 30 years,the herbaceous plants represented by Deyeuxia angustifolia invaded the tundra belt of Changbai Mountain,and the shrub tundra degenerated into the shrub grass tundra.Moreover,the nitrogen deposition in this area has been significantly increased,leading to the rapid expansion of herbaceous plants.This change of exogenous carbon and nitrogen input will greatly change the quantity and composition of soil organic carbon in the alpine tundra area,but how the soil organic carbon changes remains unclear.In this study,we compared soil organic carbon(SOC)of Rhododendron aureum communities(no invasion,mild invasion,moderate invasion and severe invasion)with four different degrees of herb invasion in the tundra zone on the west slope of Changbai Mountain,and studied the effects of herb invasion on the quantity and composition of SOC,so as to reveal the variation characteristics of SOC in shrub grass tundra.Soil organic carbon(SOC)of Rhododendron aureum communities under three nitrogen deposition treatments(0g N·m-2·a-1,10 g N·m-2·a-1 and 20 g N·m-2·a-1)with four invasive degrees(no invasion,mild invasion,moderate invasion and severe invasion)were compared to explore the effect of increased nitrogen deposition on the quantity and composition of SOC in shrub grass tundra of Changbai Mountain.The purpose of this study was to reveal the effect of increased nitrogen deposition on soil carbon pool in shrub grass tundra.The main conclusions are as follows:(1)With the increase of the invasion degree of herbs,the soil organic matter content,total nitrogen content,available phosphorus content,soil C:N and soil N:P of the shrub grass tundra of Changbai Mountain increased;but the excessive herb invasion environment restrained its increase;the content of soil available nitrogen increased with the increase of invasion degree;the total phosphorus content of soil was relatively stable,and the herb invasion had no significant influence on it.(2)With the increase of herbage invasion,the amount of soil organic carbon and its active organic carbon components in the tundra of Changbai Mountain increased first and then decreased.(3)Nitrogen addition can significantly improve the organic matter content,available nitrogen content,total phosphorus content and available phosphorus content of the shrub grass tundra of Changbai Mountain.The total nitrogen content of soil increased with the increase of N application concentration,and the high concentration of nitrogen increased the trend of soil C:N;soil N:P increased,but the effect was not significant.(4)Nitrogen addition has a significant effect on the quantity and active components of soil organic carbon.The content of soil readily oxidizable organic carbon is consistent with the change of total organic carbon content.Although nitrogen application makes the content of both increase,the promotion of medium nitrogen is more obvious,and the increase range of high nitrogen is inhibited.The content of dissolved organic carbon increased with the increase of nitrogen application concentration,and the soil microbial biomass carbon content decreased with the increase of nitrogen application concentration.(5)Under the background of nitrogen deposition,there is a close relationship between soil nutrients and soil organic carbon in the shrub grass tundra of Changbai Mountain.The total effective nutrients can affect the change of soil total organic carbon most,and the available nutrients can affect the change of soil active organic carbon most.The results showed that the amount of total organic carbon was most affected by the content of total nitrogen and soil C: N;the content of readily oxidizable organic carbon was most affected by the content of soil available phosphorus and soil organic matter;the content of soil dissolved organic carbon was most affected by the content of soil available phosphorus,soil available nitrogen and soil organic matter;soil microbial biomass carbon was most affected by soil available nitrogen content and soil organic matter content.