Comparison Of Spatial Distribution Characteristics Of Carbon And Nitrogen Elements In Soil Of Three Ecosystems In Changling County

The dynamic changes and spatial distribution of carbon and nitrogen elements in soil are important indicators of soil quality.As the largest carbon pool in terrestrial ecosystems,soil carbon pools play a great role in regulating global climate change.Soil nitrogen is the most important element for plant growth.Soil nitrogen is very important to plant growth in natural ecosystem,so studying the reserves of carbon and nitrogen in soil plays an important role in the whole terrestrial ecosystem.Changling County locate in the west of Jilin Province,it had good ecological condition,health grasslands,as well as the well-developed agriculture and animal husbandary in the early 1950 s.Over the past few decades,the eco-environmental problems in Changling County appeared frequently,such as the degradation of grassland,shrinking of wetland,increasing of saline-alkali land and decreasing of soil fertility triggered by global climate change,human activities and disturbances,as well as other various constraint conditions.To some extent,these eco-environmental problems will affect the sustainable development of agriculture and animal husbandry in Changling County,as well as the sustainable utilization of soil,water and biological resources.C and N are the most basic elements in soil.C、N content in soil directly affects soil fertility and the growth of crops and vegetation in soil.The study of soil C、N content is not only of great significance to the sustainable development of Changling County,but also to food security.In this study,three ecological systems were sampled in Changling County: farmland(corn planting),forest(poplar as the main tree species),grassland(mainly collected grassland with high species richness and Leymus chinensis as the dominant species),etc.We took 36 soil sample sites for each plot,the interval distance was 6 meters between every two sample sites,we took six layers of soil samples(0-10 cm,10-20 cm,20-30 cm,30-40 cm,40-60 cm and 60-100 cm)for each site in 0-100 cm layer of soil.So,we got 216 soil samples for one kind of ecosystem,and altogether 648 soil samples for three ecosystems.The carbon and nitrogen contents were measured with the elemental analyzer(Elementar? UNICUBE elemental analyzer,Germany).Descriptive statistical analysis and normal distribution test of carbon and nitrogen content and carbon-nitrogen ratio in different layer of soil of three ecosystems based on these data,then we compared the vertical distribution of the carbon,nitrogen and carbon-nitrogen ratio in 0-100 cm soil layer of three ecosystems;semi-variance analysis of spatial variation of soil nutrients and the corresponding spatial interpolation analysis and mapping of nutrients in surface soil were carried out.The results are as follows:(1)The degree of variation of carbon contents at all levels in the three ecosystem soils is moderate;the degree of variation of nitrogen contents in each soil layer is also moderate;the variation of C/N ratio in the topsoil of grassland is strong,while the variation of C/N ratio in the topsoil of woodland(0-10 cm)and subsurface(10-20 cm)is weak,and the variation of C/N ratio in other soil layers of the three ecosystems is moderate.(2)The carbon content in grassland soils did not show a decreasing trend with the increase of soil depth;overall,the total carbon content in farmland soils showed a decreasing trend with the increase of soil depth,but the change was small in the layer of 0-60 cm;the carbon content in woodland soils showed a significant decreasing trend with the increase of depth,and the reduction rate from surface to sub-surface layer reached 47.4%.The nitrogen content in the soil of the three ecosystems showed a decreasing trend with the increase of depth.For all the three ecosystems,the C/N ratio in soil increases with depth and then decreases slightly.There was no correlation between carbon content and nitrogen content in grassland soil,but there was significant correlation between carbon content and nitrogen content in farmland and woodland soil.(3)The carbon contents in soil of 0-100 cm of three ecosystems showed that: grassland >farmland > woodland;nitrogen contents showed that: woodland > farmland > grassland,for C/N ratio: grassland > farmland > woodland.Moreover,the soil C/N ratio of grassland and farmland was greater than 25,which reflected the obvious limitation of nitrogen nutrient.Conversion of grassland into farmland and woodland in this region reduced the carbon contents in 0-100 cm soil,so the carbon storage in soil would reduce when grassland transferred to farmland or woodland in Changling County.(4)The variation function analysis models of carbon and nitrogen content and C/N ratio in the surface soil of the three ecosystems exponential model and spherical model.Except for the carbon element and C/N ratio in the surface soil of grassland,the model simulation effect of the semi-variable function of other element indexes is better.Analysis of the semi-variable function showed that the carbon content,nitrogen content and C/N ratio of the surface soil of the three ecosystems showed a strong spatial correlation except for the moderate correlation of the carbon content of the woodland soil.