色季拉山森林和草地土壤有机碳分子结构特征

Soil organic carbon molecular structures of the alpine forest and grassland in Sejila Mountain,Tibet

【目的】为揭示高寒地区不同植被类型土壤有机碳稳定性的分子机制。【方法】以西藏东南部色季拉山森林和草地为研究对象,采用傅里叶变换红外光谱法分析不同层次(0~10、10~20、20~30、30~40和40~50 cm)土壤主要有机碳分子构成特征。【结果】1)色季拉山高寒森林和草地土壤有机碳以糖类碳为主,平均峰强度分别为1.13和0.80,其次为脂肪族甲基(CH3)和亚甲基(CH2),芳香族碳含量相对较低,森林和草地土壤峰强度平均值分别为0.26和0.22;2)土壤有机碳分子构成呈现出明显的层次特征,主要集中在表层0~20 cm,下层则相对含量下降;3)植被类型显著影响了土壤主要有机碳分子的构成,各层次土壤有机碳分子均表现为森林>草地,且糖类碳差异最大,5个土壤层次峰吸收强度差值分别为0.34、0.36、0.31、0.09和0.56;4)土壤脂肪碳/芳香碳比在0~30cm层次表现为森林>草地,而30~40和40~50cm层次土壤为草地>森林,即森林表层土壤有机碳化学稳定性较草地低,而下层则具有更强的化学稳定性;5)土壤脂肪族碳、芳香族碳含量与总有机碳之间显著正相关,与易氧化有机碳之间呈显著幂函数正相关关系(P<0.05),而糖类碳与总有机碳和易氧化有机碳之间相关性均不显著。【结论】高寒生态系统森林、草地土壤有机碳分子化学构成及稳定性不同,可能直接影响土壤有机碳的周转速率。

【Objective】The objective of this article was to elucidate the molecular mechanism of soil organic carbon stability under different vegetation types in alpine ecosystems.【Method】Sejila Mountain was selected as a model area,and the forests and grasslands were taken as the research objects.The soil organic carbon molecular composition at different soil layers(0-10,10-20,20-30,30-40 and 40-50 cm)was analyzed by Fourier transform infrared spectroscopy.【Result】1)The soil organic carbon of the alpine forest and grassland in Sejila Mountain was mainly carbohydrate carbon,with an average peak intensity of 1.13 and 0.80,respectively,followed by aliphatic methyl(CH3)and methylene(CH2).The content of aromatic carbon was relatively lower,and the average peak intensity of the forest and grassland soil was 0.26 and 0.22,respectively;2)The composition of soil organic carbon molecules showed obvious layer characteristics,mainly concentrated in the surface layer of 0-20 cm,and the relative content of the lower layer decreased;3)Vegetation type significantly affected the composition of the main soil organic carbon molecules.The soil organic carbon molecules at all layers showed forest>grassland,and the difference in carbohydrate carbon was the largest.The difference in peak absorption intensity in the 5 soil layers was 0.34,0.36,0.31,0.09 and 0.56,respectively;4)The ratio of soil aliphatic carbon to aromatic carbon in the 0-30 cm soil layer was forest>grassland,which showed grassland>forest in the 30-40 cm and 40-50 cm soil layers,indicating that the chemical stability of soil organic carbon in the surface layer of forest was lower than that of grassland,while the deeper layer had stronger chemical stability;5)There was a significant positive correlation between soil aliphatic carbon,aromatic carbon content and total organic carbon,and a significant power function positive correlation with labile organic carbon(P<0.05),while the correlation between carbohydrate carbon and total organic carbon and labile organic carbon was not significant.【Conclusion】Vegetation type has an impact on the chemical composition and stability of soil organic carbon molecules in alpine ecosystems,and may directly affect the turnover rate of organic carbon.