LI Longbo1, 2, TU Cheng-Long1**, ZHAO Zhiqi1, CUI Lifeng1, 2, LIU Wenjing2, 3
(1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002；
2. Graduate School of Chinese Academy of Science, Beijing 100049, China；
3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029.)
Abstract: The variation of soil organic carbon (SOC) contents and δ13Cvalues of SOM with depths in different soil profiles can provide the information about plant residue and accumulation, which helps to understand the process and mechanism of soil carbon cycle. In this study, five typical soil profiles from different vegetation condition in loess areas, Northwest China were selected as a case to study the profiles distribution and stable isotopic composition by physical properties and carbon isotopic composition of foliage, litter and SOC. The results showed that the SOC mainly enriched in the surface soils and decreased with increasing depths. SOC contents varied in the range of 1.1～31.2 g/kg. It was found that, the SOC content of the soils differentiated according to the vegetation condition, in the following order: broadleaves plant > coniferous plant > shrub > grassland >wasteland. The rapidly changes of layers are the 10 cm for the broad-leaved forest and coniferous forest, 20 cm for the shrubs and grassland and 5 cm for the wasteland. The SOC contents decrease slowly below the 60 cm in studied soil profiles. Compared with the other regions, the 13C was enriched and the δ13Csoc increased by 0.5‰～3.2‰ during litter degrading to SOC in surface soil. The δ13C composition of SOM increase with depth,the δ13C values of SOM are between -26.3‰ to -20.8‰ showing a significant difference exists in vertical patterns of variation, but the variation range were different in different soil profiles. In general, the variation of δ13C in different soil profiles was decreased in the following order: broadleaves plant > coniferous plant >grassland > shrub >wasteland. This may be resulted from the abundant litter materials (e.g., leaf fall) in broadleaved forest and more active microbial action in its soil and forms a higher carbon isotope fractionation of organic matter. The wasteland has seldom vegetation cover and litter was in a small amount in the topsoil and a less fractionation of SOC. The results indicated that there existed significant difference in vertical patterns of SOC contents and δ13Cvalues of SOM between different soil profiles. The stable carbon isotope geochemistry of soil organic matter shows distinct regional characteristic in loess areas.
Key words: Loess areas; soil organic carbon; stable carbon isotope
EARTH AND ENVIRONMENT Vol. 39, No.4, Tot No.286, 2011, Page 441-449
