喀斯特山区土地利用对土壤团聚体有机碳和活性有机碳特征的影响

通过选取喀斯特山区火龙果园、草丛、花椒林、乔木林和灌草丛为研究对象,对其土壤团聚有机碳和团聚体活性有机碳分布与积累特征进行研究,结果表明:各土地利用方式下的团聚体组成均以＞0.5 mm团聚体为主,其含量可占团聚体总量的82.57％-94.79％；各粒级团聚体中有机碳和活性有机碳的含量均以乔木林最高,花椒林和火龙果园相对居中,而以草丛和灌草丛较低,随土壤团聚体粒径降低,有机碳和活性有机碳的峰值基本出现在＜0.25 mm粒级团聚体,但该粒径对土壤有机碳和活性有机碳的贡献率却不足6％和4％；土壤有机碳和活性有机碳的累积均受5-1 mm团聚体中有机碳和活性有机碳含量增加的影响,该粒级团聚体对有机碳和活性有机碳的贡献率也分别达28.70％-49.47％和34.13％-47.47％,可将5-1 mm粒径团聚体作为喀斯特山区的土壤有机碳固定的特征团聚体；土壤团聚体活性有机碳含量与土壤团聚体总有机碳含量呈极显著正相关关系(r=O.8768),表明团聚体活性有机碳可以作为衡量喀斯特山区土壤团聚体有机碳动态的一个敏感性指标.

Effect of land use on the characteristics of organic carbon and labile organic carbon in soil aggregates in Karst mountain areas

Soil organic carbon is a dynamic medium of carbon transfer and is a main pathway for the circulation of carbon through soils in Karst systems. Karst systems are typically ecologically fragile areas with limited environmental capacity and resistivity. In addition, the implementation of a state policy encouraging the return of farmland to woodland (grass) and labor output in recent years has led to considerable change in land use patterns over a short period in these areas, which is bound to have far-reaching impacts on the spatial distribution pattern of soil organic carbon. Extensive previous research has investigated the response characteristics of soil organic carbon under different land use patterns. However in general, most of these studies have only investigated the total soil organic carbon in whole soils, and have rarely studied the organic carbon and labile organic carbon in soil aggregates. Organic carbon and labile organic carbon in aggregates are largely isolated from microbial activity because of the physical protection of the aggregates, and this may have a major impact on their function as soil carbon sinks. Therefore, the purpose of this study was to explore the distribution and accumulation characteristics of organic carbon and labile organic carbon in aggregates through survey, sampling, and analysis of soils in selected Karst mountain areas in China. The experiment was conducted in a small watershed in Huajiang Karst areas in southwestern Guizhou (25° 38.988'-25° 41.322'N latitude and 105° 38.031'-106° 40.505'E longitude). Samples of topsoils (0-15 cm) were collected from five kinds of typical land use patterns (Pitaya orchard, grassland, Chinese prickly ash orchard, forest and shrub-grassland). Soil aggregates were separated by dry sieving. Aggregate composition was dominated by particles > 0.5 mm which accounted for 82.57% to 94.79% of the whole soil under the different land use patterns. In all size classes of aggregate particles, forest had the highest values of organic carbon and labile organic carbon, followed by Chinese prickly ash orchard, while grassland and shrub-grassland were relatively lower. With decreasing aggregate particle size, the peak of organic carbon and labile organic carbon basically appeared in particles <0.25 mm in size. However, these aggregate particles contributed less than 6% and 4%, respectively, to the contents of soil organic carbon and soil labile organic carbon. The accumulation of soil organic carbon and soil labile organic carbon were influenced by increasing aggregate size, with 5-1 mm aggregates contributing 28.70%-49.47% and 34.13%-47.47% of the organic carbon and labile organic carbon contents, respectively. Therefore, it can be assumed that particles of aggregate size 5-1 mm hold the majority of soil carbon fixed in Karst mountain areas. In addition, the labile organic carbon content and total organic carbon content in soil aggregates were highly significantly positively correlated (r=0.8768), which suggests that labile organic carbon may be a sensitive index for measuring the dynamics of organic carbon in soil aggregates in Karst mountain areas. Our results will help to reveal the regional soil organic carbon sequestration in Karst mountain areas in China.