青藏高原中东部表土轻组碳氮含量分布及其影响因素

Distribution and impact factors of carbon and nitrogen contents in light fractions of topsoil on the central and eastern Tibetan Plateau

土壤轻组(LF)能够反映因人为活动或环境变化引起的土壤微弱改变。为探究青藏高原土壤LF含量分布及其影响因素,分析了青藏高原中东部不同植被类型下表土LF、重组(HF)及其碳氮含量和碳氮比(C/N),讨论了LF碳氮含量及C/N与环境因子的相互关系。结果表明:青藏高原中东部表土LF占土壤总有机质的比例很小(2.11%),不同植被类型表土LF含量排序为:林地>高寒草甸>高山草原>荒漠。表土轻组有机碳(LFOC)、重组有机碳(HFOC)平均含量分别为27.23%和2.39%,以林地最高(31.73%,2.64%),荒漠LFOC和高寒草甸HFOC含量最低,分别为24.63%和2.30%。轻组总氮(LFTN)、重组总氮(HFTN)平均含量分别为1.22%和0.12%,以高寒草甸最高(1.28%,0.12%),林地最低(1.14%,0.10%)。轻重组C/N均值分别为27.67和11.59,以林地最高(36.95,15.15),高寒草甸轻组C/N和高山草原重组C/N最低,分别为25.45和10.03,表明林地腐殖化程度较高,有效氮含量较低,而高寒草甸和高山草地与之相反。青藏高原中东部表土LF含量及分布受植被类型影响明显,土壤pH值是影响LF碳氮含量最重要的环境因子。

The light fraction(LF)of soil is sensitive for identifying changes in soil due to human activities or environmental changes.To explore the distribution and influencing factors of soil LF content on the central and eastern Tibetan Plateau,we measured the LF,heavy fraction(HF)and its carbon and nitrogen content and C/N ratio of topsoil at different vegetation types.We further analyzed the relationships between the carbon and nitrogen content,C/N ratio of LF and environmental factors.The results showed that the contribution of LF to total soil organic matter was small(2.11%).The content of LF in topsoil at different vegetation types followed the order of forest land>alpine meadow>alpine steppe>desert.The average contents of soil LF organic carbon(LFOC)and HF organic carbon(HFOC)in all sampling sites were 27.23%and 2.39%,respectively,with highest content in the forests(31.73%vs.2.64%).LFOC was the lowest in desert(24.63%),whilst HFOC was the lowest in alpine meadow(2.30%).The average contents of LF total nitrogen(LFTN)and HF total nitrogen(HFTN)were 1.22%and 0.12%,respectively,being highest in alpine meadow(1.28%vs.0.12%)and lowest in forests(1.14%vs.0.10%).The average value of the LF C/N ratio and HF C/N ratio was 27.67 and 11.59.C/N ratio in both LF and HF(36.95 vs.15.15)was the highest in the forests,whilst was the lowest in LF of alpine meadow(25.45)and in HF of alpine steppe(10.03).These results imply that humification degree of forests is high and the available nitrogen content is low,while an opposite pattern was found for alpine meadows and alpine steppe.The contents and distribution of the LF in topsoil on the central and eastern Tibetan Plateau significantly varied across vegetation type,while soil p H is the most important environmental factor affecting LF carbon and nitrogen contents.