Features of Organic Carbon Occurrence of Xia Laxiu Profile

Xia Laxiu region is located in the hinterland of Three Rivers area of Qinghai-Tibet plateau.The profile of Xia Laxiu was selected for organic carbon research purpose.Soil samples were collected vertically from different natural color layers and organic carbon deposited in the soil were tested and analyzed.Results showed that contents of organic carbon in different layers were significantly different(P0.05).Of all layers,contents of total organic carbon(TOC),labile organic carbon(LOC),humin(HM) carbon were highest in grass-growing layer.LOC and water-soluble substances(WSS) were found in all layers of the profile.WSS and relative contents of LOC in layers of 45 cm below showed an overall increasing trend with depth increased.Contents of fulvic acid(FA) and HM were significantly different between layers(P0.05).Absolute content of humic acid(HA) was not significant between several layers(P0.05).HA/FA values ranged from 0.14 to 2.72 and maximum HA/FA was not found in grass-growing layer.On the whole,HA/FA values of the upper part of the profile were 1,while the lower half were 1.The E4/E6 of FA varied largely,E4/E6 of HA fluctuated slightly.In conclusion,humification degree of organic substance in Xia Laxiu profile characterized by heterogeneity of components and their different contents.The period which humification degree of the grass-growing layer represented is neither the maximum one nor the minimum one.