洞庭湖湿地土壤持水能力及其影响因素研究

STUDY ON SOIL WATER HOLDING CAPACITY AND ITS IMPACT FACTORS IN THE DONGTING LAKE WETLANDS

土壤持水能力是反映土壤调节水文和供给植物耗水的重要指标,受土壤有机质、容重、机械组成和植物地下生物量的直接或间接影响。与森林和农田生态系统相比,湿地土壤持水能力关注较少。于2010年12月,对洞庭湖湿地3种主要植被（苔草、芦苇和杨树）土壤持水能力、土壤理化性质和地下生物量进行了调查,并采用主成分分析对影响土壤持水能力的主要环境因子进行了分析。结果表明：除非毛管孔隙度外,3种植被上层土壤的总孔隙度、毛管孔隙度、田间持水量和含水量差异显著,均为苔草〉芦苇=杨树,而中、下层无显著差异。沙粒为苔草≥杨树≥芦苇,而粗粉粒、细粉粒和粘粒均为杨树≥芦苇≥苔草;容重为杨树≥芦苇〉苔草,有机质为苔草=芦苇〉杨树。各级别生物量在植被类型大小顺序不一：总地下生物量、0-1mm和〉5mm径级地下生物量均以芦苇最大,而1-5mm径级地下生物量则以苔草最大。主成分分析表明,上层土壤,容重、有机质和1-5mm径级地下生物量是影响其持水能力的主要因素,而中层土壤和下层土壤,环境因子对土壤持水能力的影响很小。此研究对于洞庭湖生物多样性保护和湿地管理政策的制定具有重要意义。

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 capeity 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≥Carea 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 surfaceqayer 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.