Characteristics Of Soil Organic Carbon And Its Fractions Under Different Land Types In Qinghai Lake Region

The change of land types could significantly affect the characteristics of soil organic carbon and its fractions, and then influence the carbon cycle between soil and atmosphere. In order to understand the charactersictics of soil organic carbon and its fractions under different land types around Qinghai Lake, Xiaopo Lake and Xiannv Gulf around the Qinghai Lake were chosen as study areas.6 study sites were chosen which consisting of wetland, grassland and sands in Xiaopo Lake; and also including of meadow, swamp meadow and abandoned cultivated land in Xiannv Gulf. Soil samples were taken accoding to in 0 to 10cm,10cm to 20cm, and 20cm to 30cm depth. The contents and densities of soil organic carbon, dissolved organic carbon, readily oxidizable carbon, coarse particulate organic carbon, fine particulate organic carbon and light organic carbon fractions in different layers were studied. Meanwhile nuclear magnetic resonance test was conducted on surface soil to figure out the differences of soil organic carbon structural characteristics under different land types. The results mainly showed that:1. Content of soil organic carbon of Xiaopo Lake was between 4.49～23.66g/kg, which is significantly different among the three land types, specifically, wetland> grassland> sands. Content of soil organic carbon fractions had the same regularity. Content of soil organic carbon under different land types of Xiannv Gulf was between 17.46～23.15g/kg. Except for content of particulate organic carbon, which presented as swampy meadow> meadow> abandoned cultivated land, content of organic carbon and its fractions under different land types had the same regularity that was meadow> swampy meadow> abandoned cultivated land.2.In general, Soil organic carbon density under different land types of Xiaopo Lake and Xiannv Gulf were 0.59～2.63 kg/m2 and 2.17～3.24 kg/m2.. In Xiaopo Lake, densities of soil organic carbon and its fractions showed a regularity that wetland> grassland> sands, while in Xiannv Gulf area it was swampy meadow> meadow> abandoned cultivated land, except for soil organic carbon density, which decreased in order of meadow, swampy meadow and abandoned cultivated land.3.Through the analysis of the nuclear magnetic resonance test results on surface soil,we found that the composition of soil organic carbon structure under different land types in Xiaopo Lake was similar to that in Xiannv Gulf. The main components of organic carbon structure were alkyl carbon and alkyl carbon, and the proportion of aromatic carbon and carboxyl carbon were relatively smaller. By comparing the alkyl carbon/alkoxy carbon ratio, hydrophobic carbon/hydrophilic carbon ratio and aliphatic carbon/aromatic carbonratio, the organic carbon of wetland in Xiaopo Lake was the most stable. Whereasthe organic carbon structure stability in Xiannv Gulf was complex. By comparing the alkyl carbon/alkoxy carbon ratio and hydrophobic carbon/hydrophilic carbon ratio, the organic carbon structure stability of abandoned cultivated land was higher. However, by comparing aliphatic carbon/aromatic carbon ratio, the organic carbon of meadow was more stableTo sum up, different land types could significantly influence soil organic carbon and its fractions on their contents, densities and structural characteristics.