Characteristics And Influencing Factors Of Soil Respiration In Horqin Sandy Grassland

Soil respiration is one of the key processes of terrestrial carbon cycle,and it plays an important role in the balance of terrestrial carbon budgets,as well as global climate change and the structure and function of terrestrial ecosystems.Soil respiration is one of the main processes of soil carbon loss in sandy grassland,which is an important land use type in the arid and semi-arid regions of northern China.Affected by climate change and unreasonable human activities,the soil function of sandy grassland is degraded,and the desertification is accelerated.In the background of the national"emission peak and carbon neutrality"strategy,soil respiration in sandy grassland ecosystems is one of the main scientific focuses,as the ecological restoration of desertified land has strong carbon sequestration potential.The Horqin Sandy Land was originally the main part of the Horqin Grassland.The original landscape was a sparse forest and grassland with abundant water and grass.However,it has become the area with the most serious modern desertification in China,owing to the earlier agricultural development and the large-scale northward invasion of the interlaced area of agriculture and animal husbandry in the past century.It is also a typical area for research on desertification evolution and prevention,and its ecological restoration plays a crucial importance in maintaining the regional carbon balance.In this study,the closed air chamber method was adopted to observe the soil respiration rates in the Horqin sandy grassland during the 2021 growing season（May-October）,including total soil respiration（R_S）,heterotrophic respiration（R_H）and autotrophic respiration（R_A）.Then the temperature sensitivity index(Q₁₀)and carbon flux were calculated,thereby to explore the responses of soil respiration to changes in environmental factors.It is expected to provide basic data for in-depth research on the carbon cycle of regional ecosystems,and to provide scientific and practical basis for the formulation of sustainable ecological restoration measures and the realization of the"emission peak and carbon neutrality"goal.The main findings are as follows:（1）The monthly averaged daily dynamic of soil respiration components varied from each other,the curves of total respiration and heterotrophic respiration generally showed the characteristics of"single peak"or"multi-peak",while autotrophic respiration showed a gentle"single peak"or"bimodal"features.The maximum value of the respiration rate of each component generally occurs at 11:00～16:00,and the minimum value generally happens at3:00～6:00.The total respiration rate varied from 0.67μmol·m^-2·s^-1to 3.68μmol·m^-2·s^-1.Heterotrophic respiration rates varied from 0.24μmol·m^-2·s^-1to 1.07μmol·m^-2·s^-1.The autotrophic respiration rate varied from 0.32μmol·m^-2·s^-1to 2.79μmol·m^-2·s^-1.The contribution rate of autotrophic respiration to total respiration ranged from47%to 82%.（2）The growing season averaged daily dynamic of individual soil respiration components were positively correlated with soil temperature,atmospheric temperature,and soil water content at 10 cm（P<0.01）,and were negatively correlated with air relative humidity（P<0.01）.Total respiration and heterotrophic respiration were negatively correlated with soil water content at 30 cm（P<0.01）,while autotrophic respiration had no correlation with soil water content at 30 cm.Temperature,air relative humidity,and soil moisture explained 95%of the variation in soil respiration.Temperature（soil temperature and atmospheric temperature）was the dominant factor affecting soil respiration（explaining rate82.4%）,followed by water factor（explaining rate 12.4%）,the relative air humidity has little effect on soil respiration（explaining rate<1%）。（3）The monthly averaged dynamics of soil respiration show a"multi-peak"curve,with large differences among individual months.The maximum value of soil respiration rate generally appears in the middle of June and July,whereas the maximum value of soil respiration rate in other months appears in the first ten days or the last ten days of individual month.The peaks of soil respiration components were basically similar to the peaks of soil temperature and atmospheric temperature,showing a similar change trend.The monthly averaged contribution rate of autotrophic respiration to total respiration in the growing season was between 57.8%and 79.2%,with the order as September>August>July>October>May>June.（4）The monthly soil respiration dynamics showed that soil respiration of different components was mainly positively correlated to soil temperature and atmospheric temperature（P<0.01）.There are differences in the correlation between soil respiration and its components,air relative humidity,and soil water content at different depths in different months;in the dynamic change of the whole growing season,there were significant positive correlation between different components of soil respiration and soil temperature,atmospheric temperature,air relative humidity,and soil water contents in different depths（P<0.01）.Temperature,relative air humidity,and soil water explained 41.8%of the variation in soil respiration.Temperature was the dominant factor affecting soil respiration（explaining rate40.3%）,and relative air humidity and soil water content at different depths affected Small（explaining rate<1%）.（5）The dynamic different components of soil respiration are in consistency with the change of soil temperature and atmospheric temperature,which can be well regressed by the exponential model.The growing season averaged daily dynamic of the heterotrophic respiration has the greatest sensitivity to changes in atmospheric temperature(Q₁₀=3.5);autotrophic respiration dynamic during the growing season has greatest sensitivity to changes of soil temperature(Q₁₀=5.6).（6）The total carbon release from soil respiration in the sandy grassland growing season was total respiration 368.56 g·m^-2>autotrophic respiration 260.84 g·m^-2>heterotrophic respiration 107.73 g·m^-2.The highest total soil respiration and autotrophic respiration C release happened in August,and their rates were 109.26 g·m^-2and 84.50 g·m^-2,respectively;the highest C release of heterotrophic respiration happended in July,28.24 g·m^-2;The lowest values of soil respiration carbon release of different components were all in May,and the rates were 23.60 g·m^-2（R_S）,9.96 g·m^-2（R_H）,13.64 g·m^-2（R_A）,respectively.In conclusion,soil respiration and its components in Horqin sandy grassland are affected by environmental factors,including soil temperature,atmospheric temperature,air relative humidity,soil water content,etc.In addition,temperature is the most important factor,and There are differences in the correlations and sensitivity between different soil respiration components and temperature.The effects of environmental factors on soil respiration and its components were different in each month of the growing season.The total carbon release in the growing season was autotrophic respiration>heterotrophic respiration,and there were differences in the proportion of carbon release between heterotrophic respiration and autotrophic respiration in different months.