贵州喀斯特地区典型土壤有机碳垂直分布特征及其同位素组成

以贵州喀斯特地区两种主要土壤类型(石灰土和黄壤)为研究对象,通过测定土壤pH值、土壤有机碳(SOC)含量和植物优势种、枯枝落叶、土壤有机质的稳定同位素(δ13Csoc值)组成,探讨了该地区石灰土和黄壤剖面SOC垂直分布特征和δ13Csoc值组成差异。结果表明,与黄壤相比,石灰土剖面的SOC含量较高,石灰土剖面和黄壤剖面SOC含量变化范围分别在3.6～69.8和2.4～51.2g·kg-1。黄壤和黄色石灰土剖面SOC主要集中在0～20cm深度内,而黑色石灰土剖面从0～60cm逐步减少。黑色石灰土和黄壤剖面δ13Csoc值变化范围分别在-22.9‰～-21.5‰和-25.6‰～-22.4‰,前者较后者变化小。从剖面表土向下,黄壤剖面δ13Csoc值均出现逐步增加的趋势,而石灰土剖面δ13Csoc值从剖面表土向下出现上升-降低-不变的变化趋势。黄色石灰土剖面δ13Csoc值变幅较大,变化范围为-23.7‰～-18.2‰。在枯枝落叶转化为表层土壤有机质的过程中,石灰土剖面δ13Csoc值变幅高于黄壤。其中,黄壤剖面δ13Csoc值升高了2.6‰～3.0‰,石灰土剖面δ13Csoc值升高了5.5‰～6.3‰。上述结果揭示了SOC含量及其δ13C值随深度变化的差异,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循环过程及规律和了解剖面土壤成土过程。

Vertical distribution patterns of organic carbon and its isotopic composition in typical soil types in Guizhou karst areas of Southwest China

Taking two typical soil types (limestone soil and yellow soil) in Guizhou karst areas of Southwest China as test objects, this paper measured their pH value and organic carbon content as well as the carbon isotopic composition of dominant plant species foliage and litter and of soil organic matter (SOM), aimed to approach the vertical distribution patterns of soil organic carbon (SOC) and its stable isotopic composition (δ13Csoc) in the profiles of these two soil types. Limestone soil had a higher content of SOC, as compared with yellow soil. The SOC content in the profiles of limestone soil and yellow soil varied in the range of 3.6-69.8 and 2.4-51.2 g·kg-1, respectively. The SOC in yellow soil and yellow limestone soil mainly enriched in the 0-20 cm layer, while that in the 0-60 cm profile of black limestone soil decreased gradually with depth. The δ13Csoc in the profiles of black limestone soil and yellow soil ranged from -22.9‰ to -21.5‰ and from -25.6‰ to -22.4‰, respectively. The δ13Csoc in yellow soil increased with increasing soil depth, whereas that in limestone soil was generally high in surface layer, increased rapidly down to a depth of about 20 cm, and then decreased slowly. Compared with other soils, yellow limestone soil had a wider variation range of δ13Csoc (-23.7‰ to -18.2‰) in the profile, and the δ13C (δ13Cmax-δ13Cmin) value of SOM was 5.5‰. The δ13Csoc in limestone soil profile had a wider variation range than that in yellow soil profile during the process of litter degrading into surface soil organic matter. The δ13Csoc increased by 2.6‰-3.0‰ in yellow soil profile and by 5.5‰-6.3‰ in limestone soil profile. The results suggested that the changes in δ13Csoc and SOC content with depth in different soil profiles could provide information about the input of plant residue and its degradation and accumulation in soil, and help to reveal the mechanism of soil carbon cycle and to understand the soil formation process.