金沙江干热河谷典型林草地植物根系对土壤优先流的影响

为了明确土壤优先流形态特征以及植物根系对其形成的影响,以金沙江干热河谷元谋县苴那小流域典型植被类型银合欢人工林地和扭黄茅荒草地为研究对象,基于染色示踪法并结合Photoshop CS5和Image-Pro Plus 6.0图像处理技术,分析了2种植被下的土壤优先流形态特征和分布特征,并探究了植物根系对其的影响。结果表明: 林地和荒草地的土壤优先流染色面积具有明显差异,林地染色面积比总体随土壤深度的增加而减小,但部分地方表现出增大现象;荒草地染色面积比随土壤深度增加呈单调递减,林地优先流发生程度高于荒草地。根系对优先流的形成具有重要影响,根径0≤d≤5 mm和d>10 mm范围内,林地根长密度随着土层深度的增加呈单调递减趋势,5 mm<d≤10 mm根系根长密度在30～40 cm土层出现较大波动;荒草地各级根系根长密度均与土壤深度呈负相关关系。林地染色面积比与3 mm<d≤5 mm根径范围内的根长密度呈极显著相关,荒草地染色面积比与d≤3 mm范围的根长密度呈极显著相关;2种地类染色面积比均与1 mm<d≤3 mm范围的根重密度及d≤1 mm的根表面积呈极显著相关,与d>5 mm根径的根长密度、根重密度、根表面积的相关性不显著。研究区2种地类的土壤优先流染色面积总体变化趋势为随土壤深度的增加而减小,植物根系与土壤优先流的形成关系密切,其中,细根能显著促进土壤优先流的形成,粗根对优先流的形成具有局限性。

Effects of plant roots on soil preferential flow in typical forest and grassland in the dry-hot valley of Jinsha River,China

To clarify the morphological characteristics of soil preferential flow and the effect of plant roots on its formation, plants from the typical vegetation types of an artificial woodland (Leucaena acacia) and a dry watershed grassland (Heteropogon contortus) of Yuanmou County, Jinsha River were selected as the experimental objects. Based on the staining and tracing method combined with Photoshop CS5 and the Image-Pro Plus 6.0 image processing technology, we analyzed the morphological and distribution characteristics of soil preferential flow under the two planting types and examined the effects of plant roots. We found significant difference in soil preferential flow dyeing area between the woodland and grassland species, and the overall variation trend of the forestland dyeing area ratio decreased with increasing soil depth. The dyeing area of the grassland decreased monotonously with the increases of soil depth. The occurrence degree of soil preferential flow in forest was higher than that of grassland. Root systemaffected the formation of soil preferential flow. At the root diameter ranges of 0≤d≤5 mm and d>10 mm, root length density of the woodland showed a monotonous decreasing trend with increasing soil depth, while in the root diameter range of 5 mm<d≤10 mm, it fluctuated in the 30-40 cm soil layer. Root length densities at all the root diameter levels of desert grassland were negatively correlated with soil depth. The dyeing area ratio of the woodland was significantly correlated to root length density in the 3 mm<d≤5 mm root diameter range, while that of the grassland was significantly correlated to root length density in the d≤3 mm range. The dyeing area ratio of both land types showed significant correlation with root weight density in the range of 1 mm<d≤3 mm and with root surface area of d≤1 mm, but did not correlated with root length density, root weight density, and root surface area in the root diameter range of d>5 mm. The overall change trend of soil preferential flow dyeing area of two vegetation types in the study area decreased with increasing soil depth. Plant root system was closely related to the formation of soil preferential flow. Fine roots could promote while coarse roots may retard the formation of preferential flows.