黄土高原不同植被覆盖下土壤有机碳的分布特征及其同位素组成研究

土壤有机碳（SOC）含量及其8^13C值随深度变化的趋势可以反映植物残体的输入及其在土壤中分解累积特征，有助于揭示SOC循环过程及规律。本研究以黄土高原不同植被类型覆盖条件下的黄土剖面为研究对象，通过测定土壤属性、SOC含量和植物优势种、枯枝落叶、土壤有机质的稳定同位素组成，对该区域SOC深度分布和有机质8”C值组成差...

Distribution Characteristics of Soil Organic Carbon and Its Isotopic Composition for Soil Profiles of Loess Plateau under Different Vegetation Conditions

Variations in soil organic carbon(SOC) contents and δ13C values of SOC with depth 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 under different vegetation conditions in loess areas,Northwest China,were selected as a case to study the profile distribution and stable isotopic composition in terms of the physical properties and carbon isotopic composition of foliage,litter and SOC.The results showed that the SOC was mainly enriched in surface soils and decreased with increasing depth.SOC contents varied in the range of 1.1~31.2 g/kg.It was found that the SOC contents of the soils varied according to the vegetation conditions,in the following order:broadleaf plant > coniferous plant > shrub > grassland >wasteland.Rapid changes were noticed at the 10 cm depth for the broadleaf forest and coniferous forest,at the 20 cm depth for the shrubs and grassland and at the 5 cm depth for the wasteland.The SOC contents decreased slowly below the 60 cm depth in the studied soil profiles.Compared with other regions,13C was enriched and δ13Csoc increased by 0.5‰~3.2‰ during litter degrading to SOC in surface soil.The δ13C values of SOC increased with depth,and varied between-26.3‰ to-20.8‰,showing a significant difference in vertical patterns of variation,but the variation ranges were different in different soil profiles.In general,the δ13C values in different soil profiles decreased in the following order:broadleaf plant > coniferous plant >grassland > shrub >wasteland.This may have resulted from the abundant litter materials(e.g.,leaf fall) in broadleaf forest and more active microbial action in its soil,leading to higher carbon isotope fractionation of organic matter.The wasteland seldomly had a vegetation cover and litter was present in a small amount in the topsoil and there occurred less fractionation of SOC.The results indicated that there existed significant differences in vertical patterns of SOC contents and δ13C values of SOC between different soil profiles.The stable carbon isotope geochemistry of soil organic matter shows distinct regional characteristics in loess areas.