高寒农田土壤有机碳和全氮密度垂直分布特征及其与海拔的关系

  目的  为探讨高寒地区农田生态系统有机碳和全氮积累状况及差异特征。  方法  在祁连山中段南坡选取样点分层采集土壤样品，进行室内测定其有机碳、全氮含量及其密度垂直分布特征沿海拔的空间分布规律。  结果  研究区0 ~ 50 cm土层土壤有机碳密度在海拔2800 m处达到最大值10.18 kg m?2；全氮密度在海拔3000 m处达到最大值1.86 kg m?2，土壤有机碳密度随海拔的升高呈“U”型曲线变化，全氮密度随海拔的升高呈单峰曲线变化。 0 ~ 50 cm土层剖面上，土壤有机碳密度及全氮密度在海拔 ≤ 3000 m处随土层深度的增加而降低，在海拔3100 m处随土层深度的增加而增加。海拔高度与全氮含量、全氮密度存在显著正相关关系（P < 0.01）；土层深度与有机碳含量存在显著负相关关系，与有机碳密度和全氮密度存在极显著正相关关系（P < 0.01）。  结论  海拔和土层是影响祁连山南坡农田土壤有机碳和全氮分布的关键因子。

Vertical Distribution Characteristics of Soil Organic Carbon and Total Nitrogen Density in Alpine Farmland and their Relationships with Altitude

  Objective  Farmland soil organic carbon (C) and nitrogen（N）density are important indicators to measure soil fertility and soil quality. To explore the current status and differences of organic C and N accumulation in farmland ecosystems in alpine regions.  Method  Soil samples were collected in layers from the southern slope of the middle section of Qilian Mountains, and the spatial distribution of organic C, total N contents and vertical distribution characteristics of their density along the altitude was measured indoors.  Result  ① The soil organic C density of the 0-50 cm soil layer in the study area reached a maximum of 10.18 kg m?2 at an altitude of 2800 m. The total N density reached a maximum of 1.86 kg m?2 at an altitude of 3000 m, and the soil organic C density increased with the altitude. The increase showed a “U”-shaped curve, and the total N density showed a unimodal curve with the increase of altitude. ② On the 0-50 cm soil profile, soil organic C density and total N densities decreased with the increase of soil depth at altitudes ≤ 3000 m, and increased with soil depth at altitudes of 3100 m. ③ Altitude has a significant positive correlation with soil total N content (P < 0.01), and at the same time, it has a significant positive correlation with total N density (P < 0.01). Soil depth has a significant negative correlation with organic C content (P < 0.01), but there is a very significant positive correlation with soil organic C density and total N density (P < 0.01).   Conclusion  Altitude and soil layer are the key factors affecting the distribution of soil organic C and total N in farmland on the southern slope of Qilian Mountains.