Estimation And Spatial Distribution Of Soil Organic Carbon In Yunnan Province

Soil organic carbon pool is an important part of terrestrial carbon pool, which is about1500.00Pg (1Pg=109t). The amount of CO2released into the atmosphere from soil is10times higher than from fossil fuel burning. Thus, studying regional soil organic carbon reservation will provide important information to understand global carbon cycle. Yunnan is located in the plateau of low latitude, varied topography and changeable climate. With the study of soil organic carbon (SOC) storage and density distributed regularity in this area, and the factors that influence SOC content, we cannot only estimates the SOC pool of Yunnan Province in the national or global status, but also provide valuable reference for studies in other regions.In this study, the data collects from China’s second national soil survey in the1980s. SOC density and storage in soil layers of0-20cm and0-100cm are estimated by soil type method. Drawing a map of SOC density spatial distribution in terms of SOC density in topsoil (0-20cm) will contribute to study SOC distributed regularity in Yunnan. Statistical methods are used to get the frequency distribution characteristics of SOC density in study area. At the same time, statistical methods are also used to verify the accuracy of SOC density obtained in this paper, and will provide support for the below study (relationship between the SOC density data and the influence factors). In addition, according to the data of SOC density after natural logarithm transformation (LnSOC), the climatic conditions (temperature and rainfall) and elevation data of each sampling point, using analysis of variance we can identify the main factors affecting SOC change. Finally, compared to in the1980s and the beginning of twenty-first century the basic distribution of the land use, we try to find out the extent of SOC total storage and distribution under human-use influence.The results show that in Yunnan Province the average density of SOC estimated in the0-20cm layer is59.77t/hm2and storage is about2.30Pg; and the average density of SOC estimated in the0-100cm layer is159.95t/hm2, its reservation is about6.15Pg accounting for7.28%of the total in China and0.41%of the global terrestrial ecosystems. The spatial distribution of SOC density on the surface soil (0-20cm) presents a trend of decrease gradually from north to south, increase gradually from east to west. Areas with SOC reserves order from highest to lowest is:Sanjiang Valley Area in northwestern Yunnan, region in northeastern Yunnan, Hengduan Mountains in southwestern Yunnan, Yunnan plateau in eastern Yunnan.The factors of Rainfall, temperature, altitude have some influence in SOC reservation, but the extent of their impact is different. The effects of rainfall on the entire regional SOC storage have the same degree. The factor of temperature affect on soil organic carbon in low temperature region strongly, followed by a high temperature region. The factor of altitude has a significant effect on SOC in high elevation areas, nevertheless no significant effect on SOC in other areas.Due to lack of relevant data of SOC under different land use types, can not accurately get the size of anthropogenic impacts on SOC storage. But according to the change of land use area in Yunnan Province and the extent of SOC reservation’s change after the transformation of land use, the soil in Yunnan is the carbon "sink" in the past20years. Under the combined effects of various factors, man-made influences do not change fundamentally the basic distribution of SOC storage in Yunnan.