Effects Of Soil Physical And Chemical Properties And Exogenous Nutrients Addition On The Mean Turnover Times Of Soil Organic Carbon

Global warming caused by the increase of greenhouse gas content is one of the most severe environmental problems.And CO₂ is the most important greenhouse gas.The soil carbon pool is the most important potential source and sink of greenhouse gases,which is also the largest carbon pool in terrestrial ecosystems.The turnover time of soil organic carbon is an important index to measure the stability of soil organic carbon pool and the main factor to determine soil carbon sequestration capacity.It is an important link to achieve carbon peak and carbon neutralization globally.Soil organic carbon turnover time is influenced by many factors.In order to study the soil physical and chemical properties and exogenous nutrients addition to the influence of soil organic carbon average turnover time,23 kinds of soil was collected in 10 provinces in China.From November 2019 to November 2021,we carried out indoor cultivation experiment and short-term experiments for a long time with the method of indoor constant temperature and humidity.We analyzed the differences of soil CO₂ emission rates in different sites.We determined the physical properties of 23 kinds of soil samples,such as unit weight and field water holding capacity and chemical properties such as organic carbon content and nitrogen content.Two one-year long-term culture experiments were conducted in this study.In the first year,we selected 11 kinds of soils from Nanning,Guangxi,Changzhou,Suqian,Jiangsu and Mudanjiang,Heilongjiang for the culture experiment;in the second year,we selected 5 kinds of soils from Zigong,Sichuan,Duyun,Guizhou,Dingxi,Gansu,Hengshui,Hebei and Tongling,Anhui for the culture experiment.Different culture temperatures were set according to the local annual average temperature.At the same time,we set two water treatments of soil moisture and 25%soil moisture for culture experiments,focusing on the influences of different soil physical and chemical properties on the average turnover time of soil organic carbon.Meanwhile,four short-term culture experiments for two months were carried out in this study.We carried out the experiments with the control treatment,the treatment of biochar addition,urea addition,biochar and urea addition respectively.The specific experimental operation is to culture all 23 kinds of soil samples at 17.5℃,humidity at 25%,we set 3 replicates for each sample.Four rounds of culture experiments for each sample were carried out with adding no substances,adding 5g biochar,adding 0.2g urea,adding 5g biochar and0.2g urea.We focus on the research about effects of exogenous nutrients on the average turnover time of soil organic carbon.The main results are as follows:（1）The average turnover time of soil organic carbon was significantly different under different land use types in different climate zones.In the same area,the average turnover time of soil organic carbon under different vegetation types is also different.The spatial variation of mean turnover time of soil organic carbon was mainly related to soil physical and chemical properties（organic carbon content,total nitrogen content and field water capacity）,but was also restricted by climate factors.The simulation equation of average turnover time of soil organic carbon based on soil total nitrogen content and available potassium content can be established.The simulation equation of average turnover time of soil organic carbon under soil moisture at sampling sites was simulated as MTT=71.961e^{（0.458TN-0.007 SAK）}.The mean turnover time of soil organic carbon under 25%soil moisture was simulated as MTT=55.620e^{（0.557TN-0.008SAK）}.（2）The average turnover time of soil organic carbon decreased when the soil moisture increased to 25%.Spatial change under the soil moisture in the sampling sites mainly was limited by the soil organic carbon content,but also by the adjustment of the cumulative amount of heterotrophic respiration,when the soil moisture increased to 25%soil moisture,spatial change of soil organic carbon average turnover time was limited by soil organic carbon content and heterotrophic respiration.（3）In the four experiments of adding exogenous nutrients,the average turnover time of soil organic carbon in Taizhou of Zhejiang was the smallest,while that in Duyun of Guizhou was the largest.In 4 kinds of processing,the average turnover time of organic carbon and organic carbon content had extremely significant linear correlation.soil organic carbon average turnover time in the form of index increased with the increase of nitrogen content.The soil organic carbon average turnover time with the increase of the field capacity increased significantly.The average turnover time and unit weight has significant correlation.There is a significant exponential relation with the total porosity.The difference between the average turnover time of soil organic carbon and the content of organic carbon and the content of nitrogen had a very significant linear correlation with the addition of biochar and the addition of biochar and urea and the control.