| Soil respiration is the main form of carbon dioxide emission from soil to the atmosphere,and the flux of soil carbon emission determines whether the soil is a sink or a source of carbon in the ecosystem.There is a large area of sandy land in China,which has great potential for generating new carbon sink through vegetation restoration.Under the background of global warming,it is of great significance to the study of sandy ecosystem carbon balance by exploring the response of sandy soil respiration to vegetation restoration,which can provide a scientific basis for the management of sandy carbon sequestration.Therefore,in this study,through the method of replacing time with space,non forested mobile sandy land and Hedysarum mongolicum of different forest ages（9a,18a,30a）in Mu Us sandy land of Inner Mongolia were selected to constitute vegetation restoration gradient.In addition,the soil respiration and components in four sample plots were observed in situ,and environmental factors including root biomass,the number of bacteria and fungi in the soil,as well as soil main nutrient content were measured simultaneously,so as to explore the change law of soil respiration and components and their relationship with environmental factors during vegetation restoration.According to the research results:（1）Under different restoration gradients,there was no significant change in terms of the seasonal variation pattern of soil total respiration,and they all reached their peak value in summer while reached the minimum value in winter.With the restoration of vegetation,the annual carbon emission of total soil respiration increased significantly.The restored Hedysarum mongolicum of 30a reached 476.98 g C·m-2,which increased by 6.68 times compared with the non afforestation mobile sandy land.Furthermore,it was found in this thesis that the total carbon emission of soil respiration in the growing season（May to October）accounted for 70.94%～82.31%of the whole year,becoming the main period of carbon emission in the sandy ecosystem.（2）The seasonal variation trend of soil respiration components（heterotrophic respiration and autotrophic respiration）is similar to that of total soil respiration.The annual carbon emissions of heterotrophic respiration and autotrophic respiration have been gradually increasing with the extension of vegetation restoration time,with the variation range of 62.11～350.59 g C·m-2 and 0～126.40 g C·m-2,respectively.With the restoration of vegetation,the contribution rate of heterotrophic respiration to total soil respiration decreased from 100%to 75.54%,and the contribution rate of autotrophic respiration increased from 0%to 25.46%.Heterotrophic respiration is the main process and form of carbon emission in sandy ecosystem.（3）The existing amount of litter and the number of bacteria and fungi had a positive correlation with the heterotrophic respiration,the root biomass of each diameter class was positively correlated with autotrophic respiration,and the contents of soil organic carbon,total nitrogen,as well as the total phosphorus were all positively correlated with heterotrophic respiration and autotrophic respiration.During the process of vegetation restoration,the increase of the content of main nutrients and the number of microorganisms in sandy soil,and the accumulation of litter and underground root biomass are the leading factors for the increase of soil respiratory carbon emission in sandy land.In brief,vegetation restoration well improves the soil respiration in sandy land,and the continuous increase of its carbon emissions will inevitably result in the loss of carbon pool in the soil,warning that we should spare no efforts to strengthen the management of sandy shrub forest in the future. |
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