不同土地利用方式对土壤有机碳及其组分影响研究

测定了5种土地利用方式下（人工草地、围封样地、一年耕地、弃耕地、自由放牧样地）土壤有机碳、土壤微生物生物量碳、易氧化态碳和轻组有机碳组分含量特征，比较分析土地利用变化对典型草原土壤起源下土壤有机碳组分的变化。结果表明，1）人工草地土壤有机碳含量为（14．98±3．47）g·kg-1，围封样地的为（12．41±6．40）g·kg-1，一年耕地的为（12．20±5．59）g·kg-1，弃耕样地的为（10．39±5．08）g·kg-1，自由放牧样地的为（9．45±3．19）g·kg-1。人工草地土壤有机碳含量明显高于其他样地，围封样地和一年耕地的含量相似，自由放牧样地的含量最小。2）土壤微生物生物量碳、易氧化态碳和轻组有机碳的含量在不同土地利用方式下的变化趋势与土壤有机碳含量的变化趋势基本一致。土壤有机碳及其组分含量在土壤剖面上，随着土层深度的增加而逐渐降低。3）土壤微生物生物量碳、易氧化态碳和轻组有机碳的平均分配比率在不同类型样地范围分别为0．24％～0．66％、0．002％～0．019％和0．05％-0．25％，显示出各组分对土壤环境变化的敏感度不同，其中土壤微生物生物量碳更能反映土壤有机碳的早期变化，可以作为表征土壤有机碳变化和土壤肥力的敏感指标。

Effects of land use type on soil organic carbon and its fractions

To address how land use change affects soil organic carbon and its fractions, we sampled soil and measured contents of soil organic carbon, microbial biomass carbon, readily oxidizable carbon and light fraction carbon in five different land use types, i.e. artificial grassland （AG）, grazing exclusion （GE）, cropland （CP）, fallow （FL） and free grazing grassland （FG）. The content of soil organic carbon was （14.98 ± 3.47） g＇kg1 in AG, （12.41 ± 6.40） g.kg1 in GE, （12.20 ± 5.59） g-kg1 in CP, （10.39 ± 5.08） g＇kg-1 in FL and （9.45 ± 3.19） g＇kg＂1 in FG. Soil organic carbon content in AG was significantly higher than that in other types of land use, and that in FG was the smallest among the five land use types. Soil organic carbon content was similar between GE and CP. The pattern of microbial biomass carbon, readily oxidizable carbon and light fraction carbon among the five land use types were similar to that of soil organic carbon. The contents of soil organic carbon and its fractions decreased gradually with increasing soil depth. In the five land use types, the ratio of microbial biomass carbon, readily oxidizable carbon and light fraction organic carbon to total soil organic carbon were 0.24%-0.66%, 0.002%-0.019% and 0.05%-0.25%, respectively. These results suggest that different fractions of soil organic carbon differ in the sensitivity to environmental change. Our results confirms that the index of soil microbial carbon can be regarded as the sensitive index indicating the change of soil organic carbon and soil fertility, which can reflect the change of soil organic carbon in the early stage