宁南山区植被恢复对土壤团聚体水稳定及有机碳粒径分布的影响

土壤团聚作用和土壤有机碳固定之间密切相关.对宁南山区不同植被恢复措施和年限下土壤团聚体粒径分布及稳定性、土壤团聚体中有机碳及其组分分布进行了研究,探讨了有机碳及其组分对植被恢复的响应.结果表明,不同植被恢复措施下,土壤团聚体粒径分布表现为“V”字分布:＞5 mm和＜0.25 mm这两个粒径的团聚体含量最多,5-2 mm、1-0.25 mm团聚体的含量次之,2-1 mm粒径的团聚体含量最少.坡耕地的平均重量直径(MWD)最低,为1.4,其他植被恢复措施下土壤的平均重量直径MWD在1.9-3.1之间.不同的植被恢复措施下,0-20 cm土层和20-40 cm土层全土有机碳含量在7.4-17.7 g/kg之间、微生物碳含量分布在50.3-664.7 mg/kg之间、腐殖质碳含量在0.9-2.5g/kg之间.胡敏酸碳含量分布在0.2-0.6 g/kg,富里酸碳含量在0.6-1.9 g/kg之间.全土有机碳、微生物碳、腐殖质碳、富里酸碳均为坡耕地最低,其他植被恢复措施的有机碳、微生物碳、腐殖质碳、富里酸碳含量分别是坡耕地的1.1-2.3倍、2.0-8.4倍、1.0-2.0倍、1.2-2.4倍.不同粒径团聚体有机碳相比较,大多呈现中间高两边低的变化趋势,最大值出现在中间粒径,即5-2 mm、2-1 mm、1-0.25 mm这3个粒径.逐步回归表明,5-2 mm团聚体和1-0.25 mm团聚体有机碳含量的提高有助于土壤水稳性团聚体的形成.研究结果表明,植被恢复提高了土壤团聚体有机碳含量,在碳形态上,富里酸碳和微生物生物量碳对不同植被恢复措施的敏感度较高,胡敏酸碳含量则相对稳定.

Effects of vegetation on soil aggregate stability and organic carbon sequestration in the Ningxia Loess Hilly Region of northwest China

A close correlation exists between soil aggregation and soil organic carbon sequestration. Soil organic matter is the main material needed in the formation of soil aggregates and soil aggregates provide a place for soil organic matter to sequester carbon. The effects of different revegetation types on the aggregation of soil particles, the stability of soil aggregates, as well as carbon and fractions in soil aggregates were studied in a loess hilly-gully area; soil organic carbon and fraction's micro-response to different revegetation types are discussed. The results show the distribution of soil aggregates has a "V" distribution under a variety of revegetation and restoration measures. Small (< 0.25 mm) and large (> 5.0 mm) particle sizes form the most aggregates. The next largest aggregate size classes were 2-5 mm and 0.25-1.0 mm, while the 1-2 mm size class had the fewest aggregates. The mean weight diameter (MWD) of cropland is approximately 1.4. After land is revegetated the MWD increased to 1.9-3.1 in the soil indicating soil aggregate stability and porosity increased significantly. The aggregate stability of an area of natural grassland and also in a stand of 25-year-old Caragana korshinskii Kom. was higher than aggregate stability in a stand of 15-year-old C. korshinskii Kom. We measured various soil conditions under different revegetation types and found differences between the 0-20 cm and 20-40 cm soil layers. The soil organic carbon content was 7.4 and 17.7 g/kg; the microbial carbon content was 50.3 and 664.7 mg/kg; the carbon content of humus was 0.9 and 2.5 g/kg; the content of humic acid carbon was 0.2 and 0.6 g/kg; and the fulvic acid was 0.6 and 1.9 g/kg for the 0-20 cm and 20-40 cm soil layers, respectively. The organic carbon and the fraction in 0-20 cm soil layer were higher than measurements in 20-40 cm soil layer. The content of organic carbon, microbial carbon, humus carbon and fulvic acid carbon in the soil are the lowest in cropland; these contents under other revegetation types were 1.1-2.3 times, 2.0-8.4 times, 1.0-2.0 times and 1.2-2.4 times higher than those of cropland soils, respectively. Most of the soil organic carbon content was concentrated on intermediate sized aggregates (2-5 mm, 1-2 mm, 0.25-1.0 mm). The result of stepwise regression analysis show the higher the content of soil organic carbon was in the small and large particles (0.25-1.0 mm and 2-5 mm diameter aggregate, respectively) the more stable the water-stable aggregates were. The findings suggest vegetation restoration improved the soil organic carbon aggregate content, and in terms of forms of soil carbon, soil microbial biomass carbon and fulvic acid carbon, their content in the soil was sensitive to changes in aggregate size, while humic acid carbon was stable regardless of aggregate size.