Abstract:

Soil water holding capacity, which is usually affected by various factors, such as soil mechanical composition, soil bulk density, soil organic matter, as well as plant underground biomass, is an important index of soil capcity in hydrological regulation and water supply for plant growth. Studies on soil water holding capacity have mostly focused on cropland and forest ecosystem. Relevant studies on wetlands ecosystem are relatively less. In the present study, soil water holding capacity including soil total porosity, capillary porosity as well as field water holding capacity, and related environmental factors including soil mechanical composition, bulk density, organic matter as well as plant underground biomass, were investigated in three dominant vegetation types (Carex spp., Miscanthus sacchariflorus and Populus nigra) in Dongting Lake wetland in December, 2010. The results are as follows.(1) The soil total porosity, capillary porosity, and field water holding capacity of surface soil layer were significant different among three vegetation types, shown as Carex spp.＞M. sacchariflorus=P. nigra, but had no significant differences among vegetation in middleor lowlayer soil. (2) In soil mechanical composition, for all the three vegetation types, percent of fine silt content were highest, followed by clay, while the coarse silt and sand were least. For all the percent of soil particles content, there were little significant differences among vegetation in surfacemiddleor lowlayer soil, but we failed to find even a consistent tendency for all these three vegetation types. Soil bulk density showed as P. nigra≥Carex spp.＞M. sacchariflorus, while showed as Carex spp.=M. sacchariflorus＞P. nigra in soil organic matter content. The total, 0-1 mm and ＞5 mm diameter class underground biomass were highest in M. sacchariflorus, to be contrast, the 1-5 mm diameter class underground biomass was highest in Carex spp, which were mainly because of plant root characteristic. For all sites, soil organic matter, soil bulk density, percent of sand and fine silt content, 0-1 mm, 1-5 mm diameter class and total biomass showed significant or very significant correlations with at least one of soil water holding ability, while coarse silt, clay and 1-5 mm diameter class underground biomass showed no significant correlations based on correlation analysis. Principal component analysis combined with the followed correlation analysis showed that among various environmental factors, the three main factors affecting surfacelayer soil water holding capacity in this wetland were bulk density, organic matter as well as 1-5 mm diameter class underground biomass, to be contrast, the effects of environmental factors on middle or lowerlayer soil were neglect. In the end, based on the succession trends and management status of Dongting Lake wetlands, some suggestions and methods of wetlands protection were put forward