Nitrogen Spatial-Temporal Distribution Heterogeneity And Ecosystem Service Support In The Karst Desertification Soil

The national 14th Five-Year Plan emphasizes the need to improve the service function of eco-industrial system through desertification management.Soil nitrogen is the core element to evaluate the soil quality of desertification management,and soil nitrogen plays an important role in supporting ecosystem services.The accumulation of nitrogen in Karst desertification,nitrogen cycling process and ecosystem evolution are important to promote the ecosystem services of desertification management.According to the theories of geography,management,ecology and regional economics,the scientific issues of soil nitrogen morphology distribution characteristics of desertification management ecosystem and the support of soil nitrogen to desertification management ecosystem services are addressed.The research area will be used to analyze the heterogeneity of soil nitrogen distribution,elucidate the factors influencing the spatial-temporal heterogeneity of soil nitrogen patterns,and reveal the influence of soil nitrogen on desert ecosystem.The study reveals the support of soil nitrogen to the ecosystem services of desertification,and provides scientific and technological references for the improvement of the service function of desertification management eco-industrial system.（1）The differences of soil nitrogen distribution in spatial-temporal heterogeneity of in karst desertification were revealed,and it was clarified that soil TN and AN contents in desertification management ecosystem showed a trend of decreasing first and then increasing with the deepening of stone desertification,while soil NH₄-N and NO₃-N contents showed no obvious change pattern with the deepening of desertification,and soil TN,AN,NH₄-N and NO₃-N contents in each desertification environment were 1.05～1.05%,respectively.The soil TN,AN,NH₄-N,and NO₃-N contents were 1.05-3.54g-kg^-1,72.28-185.77mg-kg^-1,13.29-19.42mg-kg^-1,and3.07-6.20mg-kg-1,respectively,in each desertification environment,and were generally more abundant in forest and mixed agroforest ecosystems.Soil nitrogen content showed no significant difference in the dry and rainy seasons,and each nitrogen form in the ecosystems generally showed greater abundance in the dry season than in the rainy season.Soil TN,AN,NH₄-N and NO₃-N were found to be generally decreasing with the deepening of the soil layer in the kars desertification management ecosystem.Soil nitrogen patterns vary in spatial-temporal scales,and management should be strengthened in nitrogen loss-prone seasons and areas,and attention should be paid to soil nitrogen distribution and mechanisms of action.（2）The coupling relationship between soil physicochemical properties,mineral elements and nitrogen in desertification soils was found.The study showed that the effects of soil environmental factors on soil nitrogen morphology were inconsistent in the three stone desertification environments.In the potential-mild desertification environment,soil TN showed significant positive correlations with TP,TK,SOC,Cu,Cr and Pb;soil AN and NH₄-N showed highly significant positive correlations with soil AP,TP and SOC,and highly significant positive correlations with Cu,Cr and Zn;soil NH₄-N showed highly significant positive correlations with soil Na,Cu and Cr;soil NO₃-N showed highly significant positive correlations with soil AP,SOC,Ca,Mg and Cr.In the medium-intensity desertification environment,soil TN showed highly significant positive correlation with TK,soil TN showed significant negative correlation with Na;soil AN and NH₄-N showed highly significant positive correlation with AP,TK and SOC,soil NO₃-N showed highly significant positive correlation with AK,Ca and Pb;soil NH₄-N showed highly significant negative correlation with Fe and Ca.There were significant positive correlations between soil TN and AP,soil AN and Na;soil NH₄-N and Cr;and soil N0₃-N and Fe,Mg,Na,and Cu in the no-potential desertification environment.No significant correlation was shown between soil physical properties and soil nitrogen forms.The coupling relationship between soil physical and chemical properties,mineral elements and soil nitrogen was elucidated,which is conducive to revealing the factors influencing the spatial-temporal heterogeneity of soil nitrogen in karst desertification management environment.（3）The relationship between soil nitrogen and ecosystem service function indicators in stone desertification was elucidated,and it was found that soil TN,AN and NH₄-N have a greater influence on soil and water conservation function.In the desertification management ecosystem,AN has a stronger direct influence on SMC;soil NH₄-N is the nitrogen form that has the greatest direct influence on WFPS;TN is the factor that has the strongest influence on soil BD.The soil nitrogen morphological factor with the most significant degree of direct influence on soil TOC content was soil AN;soil AN had the greatest degree of direct influence on soil TP content;soil AN had the greatest degree of influence on soil TK;the soil nitrogen morphological factor with the strongest direct influence on soil p H was soil NH₄-N.That is,soil TN,AN,and NH₄-N had a greater influence on soil The effect of soil TN,AN,and NH₄-N on soil water and soil conservation function is greater in a desertification management environment.The soil and water conservation functions in the potential-light environment are GLS>ALS>FLS>RLS,respectively;in the medium-intensity desertification environment,the soil and water conservation functions are GLS>ALS>RLS>FLS,respectively;in the no-potential desertification environment,the soil and water conservation functions are FLS>RLS>GLS>ALS,respectively.To investigate the relationship between soil nitrogen and ecosystem functions,it is necessary to lay the foundation for promoting the enhancement of soil nitrogen support capacity for ecosystem services in desertification management ecosystems.It is important to pay attention to the mechanism of soil nitrogen-related ecosystem service support.