Study On Soil Carbon And Nitrogen Storage Characteristics And Influencing Factors In The South Slope Of Qilian Mountain

As the main carbon and nitrogen stock,soil plays an important role in the carbon and nitrogen cycle processes of global terrestrial ecosystems and in regulating global climate change with the increasing global warming.The study of soil carbon and nitrogen reserves has become an important part of the global soil carbon and nitrogen cycle research,which is of great significance for studying the response of soil carbon and nitrogen to global climate change and evaluating the quality of terrestrial ecosystems.The ecological status of the southern slope of Qilian Mountain is very important because it is not only an important ecological security barrier in the arid region of Northwest China,but also an important part of the ecological function zone of Qilian Mountain and Qilian Mountain National Park.Therefore,in the context of continued warming of the global climate,the research of the carbon and nitrogen stock and their influencing factors in the southern slope of the Qilian Mountain has important scientific value and practical significance for the sustainable economic and social development of the region.In this paper,the southern slope of Qilian Mountain is taken as the study area and which is studied to explore the vertical distribution characteristics and differences of soil total carbon and total nitrogen content and density and the main influencing factors under five different ecosystems such as forest,grassland,shrub,wetland,and cultivated land,by using the method of field sampling,experimental analysis and mathematical statistical analysis.Besides,we selected five different GIS spatial interpolation methods to simulate the spatial distribution of soil carbon and nitrogen content and stock and selected the OK?LU method to estimate the soil carbon and nitrogen stock of five different ecosystems.What we do is to provide data reference for the study of the soil carbon and nitrogen cycle,the rational use of land resources,and management measures to deal with future climate change.The main research results as follows:(1)In general,the soil total carbon and total nitrogen contents of different ecosystems showed a decreasing trend with increasing soil depth.The average value of soil total carbon content of different ecosystems are shown as:Wetland(143.63g·kg^-1)>woodland(79.08 g·kg^-1)>shrub(58.77 g·kg^-1)>grassland(45.12 g·kg^-1)>cultivated land(35.56 g·kg^-1).The average value of soil total nitrogen content of different ecosystems are shown as:Wetland(11.49 g·kg^-1)>woodland(4.65 g·kg^-1)>shrub(4.65 g·kg^-1)>grassland(3.78 g·kg^-1)>cultivated land(3.28 g·kg^-1).The difference in soil total carbon and total nitrogen content in different soil layers of the same ecosystem was significant(p<0.05).There are significant differences in soil total carbon and total nitrogen content between different ecosystems in the same soil layer(p<0.05).The average value of soil total carbon density of different ecosystems is in the order:Wetland(8.60 kg·m^-2)>woodland(6.09 kg·m^-2)>shrub(5.61kg·m^-2)>grassland(4.47 kg·m^-2)>cultivated land(3.99 kg·m^-2).The average value of soil total nitrogen density is in the order:wetland(0.67 kg·m^-2)>shrub(0.44kg·m^-2)>forest land(0.4 kg·m^-2)>grassland(0.37 kg·m^-2)=cultivated land(0.37kg·m^-2).The average value of soil total carbon density of cultivated land is the lowest,and significantly lower than other four ecosystems(p<0.05).Both of the average value of total carbon and nitrogen density of wetland soil are the highest,which is significantly higher than other four ecosystems(p<0.05).(2)The correlation between soil carbon and nitrogen content in different soil layers of different ecosystems and various influencing factors is different.Specifically,the total carbon content of grassland soil is negatively correlated with soil bulk density,latitude,altitude,and precipitation as a whole.The forest land is negatively correlated with soil bulk density and positively correlated with NDVI.The wetland has a significant negative correlation between the soil bulk density and the total carbon content of two soil layers in 30?40 cm and 40?50 cm,the soil bulk density and p H value of shrub soil in 0?10 cm,the soil total carbon content in other soil layers was only significantly negative correlation with the soil bulk density,while the soil total carbon content in cultivated land was only 0?10 cm in the surface layer.There was a significant negative correlation between air temperature and NDVI,and there was no significant correlation between other soil layers and various factors.In terms of soil total nitrogen content,there are more soil layers significantly related to soil bulk density,which is manifested in that the total nitrogen content of grassland soil is negatively related to soil bulk density,p H value and latitude as a whole,and positively related to longitude.With the gradual increase of grassland soil depth,the factors significantly related to soil total nitrogen content are gradually decreasing.On the whole,the total nitrogen content of forest land was negatively correlated with soil bulk density,and positively correlated with NDVI and NPP.There was a significant negative correlation between soil total nitrogen content and soil bulk density in the bottom two layers of wetland.There was a significant negative correlation between the total nitrogen content and the soil bulk density,and also with the soil p H value.There was no significant correlation between the total nitrogen content and the factors in cultivated land.(3)Through the comparative analysis of five spatial simulation methods,the simulation accuracy of the kriging method based on land use type correction(OK?LU)is higher,which is more suitable for spatial simulation of soil carbon and nitrogen content and reserves in the south slope of Qilian Mountain.Specifically,the average value of soil total carbon content is 21.68 g·kg^-1?90.09 g·kg^-1,the average value of soil total nitrogen content is in the range of 2.18 g·kg^-1?6.31 g·kg^-1.The spatial distribution of soil carbon and nitrogen showed that the high value areas were mainly distributed in the southeast of Menyuan County and the middle of the study area and the low value areas were mainly distributed in the southwest of Menyuan County and the northwest of the study area.The average value of soil carbon and nitrogen content in forest land is higher than that in other ecosystems,and the average value of soil carbon and nitrogen content in cultivated land is the smallest.The order of the average value of soil carbon and nitrogen content is forest land>shrub>wetland>grassland>cultivated land.The average value of soil carbon and nitrogen density in different ecosystems generally shows a decreasing trend with the increase of soil depth.The average value of soil carbon and nitrogen density in different soil layers is higher in shrub and forest land,smaller in wetland and arable land.The overall spatial distribution of soil carbon and nitrogen density shows that the high value areas are mainly concentrated in the middle of the study area and the southeast of Menyuan County,while the low value areas are concentrated in the northwest of the research area and the southwest of Menyuan County.(4)The soil tatal carbon and nitrogen stocks of different ecosystems generally showed a decreasing trend with the increase of soil depth.The spatial distribution of soil carbon and nitrogen stocks are consistent with the spatial distribution of soil carbon and nitrogen density.The total carbon and nitrogen stock of grassland soil are the highest,and the total carbon and nitrogen stocks of cultivated land soil are the lowest.The total carbon stocks of different ecosystems are shown as:grassland(2.46×10⁸t)>shrub(8.36×10⁷t)>wetland(5.22×10⁷t)>forest land(2.10×10⁷t)>cultivated land(1.07×10⁷t),the order of total soil nitrogen stocks is:grassland(1.97×10⁷t)>shrub(6.62×10⁶t)>wetland(4.35×10⁶t)>woodland(1.45×10⁶t)>cultivated land(9.16×10⁵t).