Factors Affecting Soil Organic Carbon Density （SOCD） and Total Nitrogen Density （TND） in Inner Mongolian Steppe

在内蒙古草原区选取94个样点，涵盖耕地、退耕地、人工林和草原4种土地利用类型，根据土壤质地将草原细分为沙质草原和非沙质草原。通过对这些样点土壤有机碳密度（SOCD）和全氮密度（TND）的研究，发现在内蒙古草原区，SOCD主要受到土壤质地的影响，黏粒（〈2gm）、粉砂（2～16μm）和细粉砂（16～63μm）的含量越高，SOCD越高。而TND同时受到土壤质地和土地利用类型的影响，分布在非沙质土壤的草原具有最高的TND。耕作不会导致SOCD显著降低，但是会造成TND降低。人工林不能显著提高土壤养分含量，相反，由于人工林对养分和水分的需求很大，可能导致土壤肥力的降低。此外，草原区温度越高，土壤养分越低，这预示着在全球变暖的背景下，这一地区的土壤可能成为重要的碳源。植被退化越严重，土壤养分越低，因此保护草原区的植被免受过度放牧的影响非常重要。

Factors Affecting Soil Organic Carbon Density (SOCD) and Total Nitrogen Density (TND) in Inner Mongolian Steppe

The authors collected soil samples from 94 profiles in Inner Mongolia covering 4 land use types: cropland,abandoned cropland,artificial forest and steppe,in which steppe can be further classified into sandy steppe and non-sandy steppe.It is found that soil organic carbon density(SOCD) is affected by soil texture.It increases with the content of clay(<2 μm),fine silt(2-16 μm) and coarse silt(16-63 μm).However,total nitrogen density(TND) is affected both by soil texture and land use types.Non-sandy steppe has the highest TND.Cultivation leads to the decreasing of TND but not SOCD.The expected increase in SOCD of artificial forest does not realize.Since the requirement of soil nutrient and water is large,artificial forest may even cause strong negative effects on soil fertility and sustainability.It is also found that soil nutrient decreases when mean annual temperature(MAT) increases.Under global warming,the region may turn to an important carbon source.Soil nutrient decreases with vegetation degradation,so the protection of steppe vegetation from over grazing is very important.