华南花岗岩侵蚀区不同植被类型坡面土壤有机碳分布和团聚体稳定性

植物是影响土壤有机碳含量和土壤团聚体稳定性的重要因素。选取华南典型花岗岩侵蚀区荒草地、桉树林、湿地松林和木荷林4种植被类型径流小区的土壤为研究对象,分析测定不同坡位、不同土层深度的土壤有机碳特性和团聚体稳定性等指标,评价不同植被类型对土壤养分的分布特性以及团聚体稳定性差异,明确花岗岩侵蚀退化区较为理想的生态恢复措施,旨在为合理利用土壤、重建坡面植被和改善土壤结构提供科学依据。结果表明:土壤总有机碳(TOC)、全氮(TN)和溶解性有机碳(DOC)含量随土层加深逐渐降低,而林地小区土壤碳氮比(C/N)则相反,荒草地碳氮元素的坡面变异系数(CV)显著高于其他3种林地,其中桉树林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低40%,56.18%,68.5%和25.81%;湿地松林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低62.73%,33.71%,46.46%,58.06%;木荷林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低41.82%,38.2%,51.18%,48.39%,表明林地较荒草地更有利于土壤碳氮在坡面的均质化和有机质的积累。荒草地和木荷林地0.25 mm粒径以上的团聚体在上、中坡位的质量分数显著高于其他植被类型,而林下植被生物量较高的木荷林地的平均质量直径(MWD)和几何平均直径(GMD)显著高于其他植被类型。其中木荷小区水稳性团聚体平均质量直径(MWD)较荒草地、桉树和湿地松分别高20.10%,19.58%,23.20%;几何平均直径(GMD)较荒草地、桉树和湿地松分别高20.00%,19.54%,22.23%,表明在花岗岩侵蚀区林地空间结构较好的林草模式有利于土壤有机碳的积累和土壤结构的稳定。

Soil Organic Carbon Distribution and Aggregate Stability on the Slope of Different Vegetation Types in Granite Erosion Region of South China

Vegetation is an important factor affected soil organic carbon content and soil aggregate stability. In this study, the soil of runoff plots in four vegetation types, which were wasteland, Eucalyptus forestland, Slash pine forestland and Schima superba forestland in the typical granite erosion region of south China, was selected as the research objects. The characteristics of soil organic carbon and aggregate stability in different slope positions and soil depths were analyzed, and the effects of different vegetation types on the distribution characteristics of soil nutrients and the soil aggregates stability were evaluated. The ideal ecological restoration measures for granite erosion and degradation region was identified, so as to provide a scientific basis for the rational use of soil, reconstruction of slope vegetation and the maintenance of soil structure stability. The results showed that the content of soil total organic carbon (TOC), total nitrogen (TN) and dissolved organic carbon (DOC) gradually decreased with the increasing of soil depth, while the soil C/N ratio in the forestland plots was opposite, and the slope coefficient of variation (CV) of carbon and nitrogen elements in the wasteland plot was significantly higher than those in the other three kinds of forestland, among them, the CV in slope distribution of TOC, TN, DOC and C/N in Eucalyptus forest land was 40%, 56.18%, 68.5% and 25.81% lower than those in wasteland; the CV of the slope distribution of TOC, TN, DOC and C/N in Slash pine forestland decreased by 62.73%, 33.71%, 46.46% and 58.06%, respectively, compared to the wasteland; the CV in slope distribution of TOC, TN, DOC and C/N of S. superba decreased by 41.82%, 38.2%, 51.18% and 48.39%, respectively, compared to the wasteland, indicating that the forestland was more conducive to the accumulation of soil carbon and homogenization of nitrogen and carbon on the slope. The mass fraction of aggregates above 0.25 mm grain size on the upper and middle slopes in the grassland and S. superba forestland were significantly higher than that in other vegetation types, while the mean weight diameter (MWD) and geometric mean diameter (GMD) of the S. superba forestland with high biomass of understory vegetation were significantly higher than those of other vegetation types. The MWD of S. superba forest was 20.10%, 19.58% and 23.20% higher than that of wasteland, Eucalyptus and Slash pine forest, respectively; the GMD of S. superba forest was 20.00%, 19.54% and 22.23% higher than that of wasteland, Eucalyptus forest and Slash pine forest, respectively, which indicated that the forest grass model with better spatial structure of forest and grass in the granite erosion region was more conducive to accumulation of soil organic carbon and the stability of soil structure.