封育是当前恢复和改良内蒙古草地的重要措施，也是实现草地固碳效应最有效的途径之一。本文利用内蒙古封育32年和自由放牧的羊草草地，分析了其土壤有机碳组分、土壤团聚体和土壤腐殖质组分碳含量的变化，并运用13 C核磁共振波普法对土壤腐殖质的有机碳组分进行波普分析，探讨了长期封育对羊草草地土壤有机碳组分和土壤有机质结构的影响，期望能为科学地评估长期封育状况下草地固碳效应及其稳定性提供理论依据。实验结果表明：长期封育显著提高了草地土壤有机碳含量；在土壤有机碳组分中，除土壤微生物碳（MBC ）含量降低外，其碳组分含量都相应增加。其中，易氧化有机碳（EOC）含量增加最为明显，长期封育草地是自由放牧草地土壤的4．53倍；长期封育显著提高了草地土壤0．25～2 mm 团聚体所占比例及其有机碳含量；长期封育提高了草地土壤腐殖质中的胡敏酸碳（HAC）、胡敏素碳（HUC）含量和胡敏酸／腐殖质碳，降低了富里酸碳（FAC）的含量，封育草地土壤的 H AC／FAC是自由放牧草地土壤的5．66倍。此外，长期封育草地土壤的脂族碳含量显著增加，芳香度相应增加，疏水碳／亲水碳增大。总之，长期封育不仅提高了草地土壤有机碳贮量，还能改善草地土壤结构、增强土壤有机碳的稳定性。
Characterization of the vertical distribution of soil organic carbon(C), nitrogen(N), and phosphorus(P) may improve our ability to accurately estimate soil C, N, and P storage. Based on a database of 21 354 records in 74 long-term monitoring plots from 2004 to 2013 in the Chinese Ecosystem Research Network(CERN), we built fitting functions to quantify the vertical distribution of soil C, N, and P(up to 100 cm depth) in the typical Chinese terrestrial ecosystems. The decrease of soil C, N, and P content with depth can be well fitted with various mathematical functions. The fitting functions differed greatly between artificial(agriculture) and natural(desert, forest, and grassland) ecosystems, and also differed with respect to soil C, N, and P content. In both the artificial and natural ecosystems, the best fitting functions were exponential functions for C, quadratic functions for N, and quadratic functions for P. Furthermore, the stoichiometric ratios of soil C, N, and P were ranked in descending order: grassland > forest > agriculture > desert, and were also associated with climate. This study is the first to build the fitting functions for the profile distribution of soil C, N, and P in China at a national scale. Our findings provide a scientific basis to accurately assess the storage of C, N, and P in soils at a large scale, especially for the integrative analysis of historical data.
