Changes In Soil Carbon,Nitrogen,Phosphorus Content And Ecological Stoichiometric Ratio During The Degradation Of Zoige Wetland

Climate change and the mankind destruction for a long time have caused serious degradation of the Zoige wetland.The contents of nutrient elements in soil changed dramatically.However,different scholars have gotten different results of the change in soil carbon,nitrogen and phosphorus during the degradation of the Zoige wetland.The response of soil carbon,nitrogen and phosphorus ratio to wetland degradation and the effect of stoichiometric ratio on nutrient element circulation during the degradation are still unclear.In this study,the Huahu and Maqu wetland in Zoige wetland were taken as research objects.We studied the distribution,the stoichiometric ratio and influencing factors of soil carbon,nitrogen,phosphorus in the degradation of Zoige wetland.This study will reveal the response mechanism of soil carbon,nitrogen and phosphorus ratio to wetland degradation and provide a theoretical reference for the future restoration,management and protection of the Zoige wetland.The main research results were as follows:1.Along the degradation gradient,the soil water content was firstly increased and then decreased.The water content range of Huahu research area was 29-314%,and that of Maqu research area was 78-270%.PCA analysis showed that there was a positive correlation between water content and aboveground biomass,soil organic carbon(SOC),total nitrogen(TN).2.The contents of SOC and TN were 39-253 g·kg-1 and 1.4-18 g·kg-1.Along the degradation gradient,both SOC and TN increased firstly and then decreased.However,the SOC and TN contents in Huahu research area showed as follows: the changes from swamp to alpine meadow were not significant,and SOC and TN contents from alpine meadow to desertified alpine meadow significantly reduced.The Maqu research area showed that SOC and TN contents from swamp to swamp meadow increased significantly,while the changes from alpine meadow to heavily degraded alpine meadow was not significant.The total phosphorus(TP)content varied in the range of 0.3-2 g·kg-1.It increased firstly and then decreased along the degradation gradient and that of the wetland stage was smaller than the meadow stage.3.The variation range of soil C/N,N/P and C/P was 13-32,1.3-15.2 and 31.7-204.7,respectively.Along the degradation gradient,soil C/N increased firstly and then decreased,but there was no significant difference between the swampy meadow stage and the alpine meadow stage in the Huahu research area,while the alpine meadow stage in the Maqu research area was significantly higher than the swampy meadow stage.Except for the swampy meadow stage,the soil C/N in the Huahu research area was lower than that of Maqu.On the whole,soil C/P and N/P were higher in wetland stage than in meadow stage,and soil N/P was lower than 10 in degraded meadow stage of Huahu research area and Maqu in summer.Thus,the following conclusions were drawn:1.The changes in soil water content were the leading factor for the differences in SOC,TN and TP content along the degradation gradient.Soil P was accumulated during the degradation of the swamp into meadow.Soil C and N sequestration were improved in the process of swamp degradation to swampy meadow.This was due to that the decrease of water level in swamp stage will promoted the growth of plants.Although the decomposition of soil C and N was accelerated,the significant increase of plant biomass also significantly increased the C and N content of soil and the land became fertile.During the meadow degradation,soil C and N sequestration decreased.The dramatic loss of water in the Huahu research area was not conducive to the growth of plants.Although the decomposition of soil C and N slowed down,the significant reduction of plant biomass led to a significant decrease in SOC and TN content,resulting in barren and even sandy land.The water content in Maqu research area was not significantly changed and still maintained at a high level,so it had little impact on plant growth,leading to the insignificant change in soil C and N content.This suggested that the disturbance intensity in Huahu meadow stage was higher than that in Maqu.In the future,the restoration of the degraded alpine meadow stage in Huahu should consider the improvement of soil moisture.2.On the whole,moderate disturbance to the swamp would increase soil C and N sequestration capacity.In summer,the degraded meadow in Huahu and Maqu research area were N limited,and P was abundant.Thus it is very important to replenish N for the future wetland restoration in this region.