宁夏典型天然草地土壤团聚体稳定性及其有机碳分布特征

土壤团聚体作为土壤结构的基本单元和土壤有机碳存在的重要场所，对维系土壤质量和生态环境可持续发展具有重要作用。为探究宁夏天然草地土壤团聚体稳定性及其有机碳分布特征，以宁夏4种典型的天然草地（草甸草原、温性草原、草原化荒漠和荒漠草原）为研究对象，系统开展研究。结果表明：草甸草原、温性草原和草原化荒漠各粒级机械团聚体和水稳性团聚体含量均呈现随粒径减小而先减小后增大趋势，荒漠草原机械团聚体含量呈现随粒径减小而先减小后增大的趋势，水稳性团聚体含量呈现随粒径减小逐渐增大的趋势；且草甸草原和温性草原机械稳定性和水稳性团聚体在0-10 cm、10-20 cm和20-40 cm 3个土层均以>0.25 mm大团聚体为主，草原化荒漠和荒漠草原水稳性团聚体均以<0.25 mm的微团聚体为主。4种草地类型机械团聚体和水稳性团聚体MWD和GMD，以及各粒级土壤团聚体有机碳含量均表现为草甸草原和温性草原显著高于草原化荒漠和荒漠草原。草甸草原和温性草原在3个土层深度均以>0.25 mm的大团聚体对有机碳的贡献率最高，分别达到43.86%、59.26%、58.89%和58.02%、54.03%、57.15%；草原化荒漠和荒漠草原在3个土层深度，均以<0.25 mm的微团聚体贡献率高，分别达到了60.37%、55.86%、54.33%和75.61%、78.34%、78.74%。结果表明：草甸草原和温性草原较草原化荒漠和荒漠草原土壤团聚体稳定性更高，更有利于土壤有机碳累积。

Distribution characteristics of soil aggregates and its organic carbon in typical natural grassland of Ningxia

As a basic unit of soil structure and an important site for the soil organic carbon, soil aggregate plays an important role in maintaining the soil quality and sustainable development of ecological environment. In order to understand the soil aggregate stability and organic carbon distribution, 4 typical natural grasslands including meadow steppe, warm steppe, steppe desert and desert steppe in Ningxia were studied. The results showed that the content of mechanical-stable aggregates and water-stable aggregates of meadow steppe, warm steppe and steppe desert indicated a decreased first and then increased trend with reduction of grain size. And the content of mechanical-stable aggregates took on the decreased first and then increased trend, while the water-stable aggregates took on increasing trend with reduction of grain size in desert steppe. The mechanical-stable and water-stable aggregates of meadow steppe and warm steppe were dominated by macroaggregates (>0.25 mm) in 0-10 cm, 10-20 cm and 20-40 cm soil layers, while the water-stable aggregates of steppe desert and desert steppe were dominated by micro-aggregates (<0.25 mm). The mean weight diameter (MWD) and geometric mean diameter (GWD) of mechanical-stable aggregates and water-stable aggregates and the soil aggregate organic carbon content showed that the meadow steppe and warm steppe were significantly larger than steppe desert and desert steppe. Aggregates of >0.25 mm made the largest contributions to soil organic carbon reaching 43.86%, 59.26%, 58.89% and 58.02%, 54.03%, 57.15% in meadow steppe and warm steppe, respectively. Aggregates of <0.25 mm made the largest contributions to soil organic carbon reaching 60.37%, 55.86%, 54.33% and 75.61%, 78.34%, 78.74% in steppe desert and desert steppe, respectively. The results showed that the meadow steppe and warm steppe were more stable in soil aggregates than steppe desert and desert steppe, and they were more beneficial to soil organic carbon accumulation.