中文摘要：

长期过度放牧或不合理放牧使内蒙古草地大面积退化,并出现了以小叶锦鸡儿为主的草地灌丛化现象,显著增加了草地土壤碳氮贮量的空间异质性。如何科学地设置取样点,已成为准确评估该地区灌丛化草地土壤碳氮贮量及其碳汇功能所亟须解决的重要问题。本研究在锡林河流域附近选取了3个不同退化程度的灌丛化草地,分析了灌丛化草地不同位置（灌丛内部、灌丛边缘和灌丛外部）的碳氮含量和贮量的差异。结果表明,灌丛化草地碳贮量在不同取样位置具有较大的差异;以轻度退化草地为例,0-100cm土壤碳贮量为灌丛内部（8831.26g C/m^2）〉灌丛边缘（8174.59g C/m^2）〉灌丛外部（7716.48g C/m^2）。如果将灌丛内部、灌丛边缘和灌丛外部分别取样后计算的值作为灌丛化草地土壤碳贮量的真实值,则仅从灌丛内部取样会造成5.74%-27.62%的误差,仅在灌丛边缘取样会造成-3.76%-9.81%的误差,仅在灌丛外部取样的误差为-6.06%--0.70%。虽然内蒙古地区灌丛化草地的碳氮含量存在显著的空间异质性（或沃岛效应）,但由于灌丛面积与土壤碳氮含量在不同程度退化草地内存在密切的负相关关系,因而,从灌丛外部取样的传统方法能准确评估内蒙古地区灌丛化草地的土壤碳氮贮量。

英文摘要：

Large areas of grasslands have been subjected to severe degradation in Inner Mongolia because of long-term overgrazing.Thicketization,associated with an increase in Caragana microphylla,on Inner Mongolian grasslands has resulted in an apparent increase in heterogeneity of the distribution of soil nutrients.Consequently,setting up appropriate sampling points is crucial for accurately evaluating storage of soil carbon（C）and nitrogen（N）.In this study we selected three grasslands with different levels of thicketization（different levels of degradation）and analyzed the differences in soil C and N from soil sampled from underneath,the canopy edge,and between C.microphyllashrubs.Soil C and N contents differed at different sampling locations.In lightly thicketed grasslands,carbon storage in the 0-100 cm soil layer varied;soil underneath shrub canopies,the canopy edge and between shrubs contained 8831.26 g C/m^2,8174.59 g C/m^2 and 7716.48 g C/m^2 respectively.Sample variation was greatest under the shrubs,intermediate at the canopy edge and least between shrubs.Our findings suggest that traditional sampling between shrubs can be used to accurately estimate soil C and N content in thicketed grasslands in Inner Mongolia.However,apparent spatial heterogeneity in soil nutrients was found;soil C and N contents were negatively correlated with shrub size in different grasslands.