Carbon And Nitrogen Dynamics Of Primary Succession In Hailuogou Glacier Retreated Area

Hailuogou glacier is located in the eastern slope of Gongga mountain,and the primary succession sequence formed by glacier retreated is one of the best preserved original succession sequences of vegetation in the world.In this study,eight fixed plots were set up in different stages of vegetation succession sequence in Hailuogou glacier retreated area of Gongga mountain.The carbon and nitrogen content of each component in each stage of ecosystem was measured in detail,and the storage and distribution pattern of carbon and nitrogen in ecosystem were calculated based on vegetation biomass,and the cycling characteristics of carbon and nitrogen in different stages of succession were analyzed.On the one hand,it can enrich the research data of carbon and nitrogen storage and carbon and nitrogen cycle of forest ecosystem in China.On the other hand,it is of great significance to accurately describe the continuity and integrity of the whole primary succession process and how to guide vegetation restoration according to the principle of primary succession.The main research results are as follows:(1)In the process of primary succession,species are constantly replaced,and the dominant species in the community in each succession period are different.As a result,biodiversity tends to be rich and community structure tends to be stable.During the whole succession process,the biomass of the ecosystem increased from 7.92 t/ha to419.42 t/ha.The biomass of tree layer is the main part of the forest ecosystem,followed by the litter on the ground,and the contribution of undergrowth to the biomass is small.(2)In the whole succession sequence,due to the different physiological characteristics of different species and the different physiological and ecological functions of each organ,the carbon and nitrogen contents of different species and organs are different.In terms of organs,the carbon content of branches is the largest,while the carbon content of leaves and trunks is smaller;the nitrogen content is the highest in leaves and the smallest in trunks.The content of carbon and nitrogen in Undergrowth Plant layer was shrub layer > herb layer > ground cover layer.The carbon content of crude woody residue was significantly higher than that of litter in each period,while the nitrogen content of litter was significantly higher than that of crude woody residue.In the whole succession process,the carbon content of A0 layer was higher than that of A layer,and the nitrogen content was greatly affected by litter,which showed different performance in different stages.(3)With the succession going on,the carbon and nitrogen storage of forest ecosystem in glacier retreat area increased from the initial 3.83 t/ha and 0.42 t/ha to the final 350.80 t/ha and 14.19 t/ha respectively.Arbor layer and soil are the most important carbon and nitrogen reservoirs in the ecosystem,while the carbon and nitrogen elements stored in Undergrowth plants and litter are less.(4)The nutrient cycling coefficient was 0.57,0.74 and 0.86 in S2,S5 and S8,respectively;the turnover time was 25.38 a,23.68 a and 28.42 a respectively,among which the turnover time of carbon element was about three times that of nitrogen element,indicating that nitrogen element was relatively active and played a more important role in the growth and development of vegetation in the community.The absorption coefficient and utilization coefficient decrease continuously with succession.From the initial stage of succession to the late stage of coniferous forest,the carbon and nitrogen uptake and return showed a trend of gradual increase,while the annual reserve increased first and then decreased.Different succession stage of nitrogen flow in the ecosystem is also different,this is mainly due to the different species of different physiological characteristics and nutrient utilization strategy,hardwood species tend to accelerate nutrient cycling,make its full flowing in the ecosystem,and conifer tend to keep nutrient elements in the body,the nutrient cycling slower,turnaround time is longer than the other.