洞庭湖湿地杨树人工林对土壤理化性质的影响

近几十年来的杨树大面积种植引发了人们对洞庭湖湿地生态系统生态环境恶化的担忧。本研究以11龄与5龄杨树林为对象,以邻近的典型湿地植被南荻为对照,拟阐明杨树人工林对土壤理化性质的影响。结果表明,对土壤物理特性而言,杨树的种植加速了土壤水分的散失,对水分改变的趋势随林龄的增加而增大;杨树人工林改变了土壤粒径组成,致使粘粒与粉粒的降低、砂粒的增加,砂粒化趋势随林龄的增大而增强;对土壤化学特性而言,杨树人工林导致土壤中层(20-60 cm)电导率的降低,以及下层(60-100 cm)pH值的升高,对土壤全磷含量无明显影响,总体上降低了土壤全钾含量;引起土壤40-60 cm全氮含量的降低,降低趋势随林龄的增加而增大。此外,两种杨树林对土壤全碳的影响不同,低林龄能降低土壤全碳含量,而高林龄有利于碳的增加。可见,大规模种植杨树导致土壤特性的重要改变必将对湿地生态系统产生深远的影响。

Effects of Poplar Plantations on Soil Physical and Chemical Characteristics in Dongting Lake Wetlands

In recent decades, large-scale poplar plantations have caused great concerns about their negative effects on ecological environments in the Dongting Lake wetlands. In this paper, five and eleven years of poplars were chose to study the effects of poplar plantation on soil physical and chemical characteristics in comparison with adjacent Miscanthus sacchariflorus, an indigenous vegetation of the Dongting Lake. For soil physical properties, soil water content was lowest in M. sacchariflorus and highest in 11-year poplars. Poplar plantation changed soil particle-size distribution and decreased the percentage of clay and silt but increased that of sand. The increased percentage of sandy was increased with increased stand age. For soil chemical properties, poplar plantation decreased electrical conductivity in middle soil (20-60 cm), total potassium in all layers of soil, but increased pH in subsoil (60-100 cm). There was no difference in phosphorus among three vegetations. Additionally, poplar plantations also decreased total nitrogen in soil layer of 40-60 cm, and the effect was increased with increased stand age. Finally, both poplars have different effects on total carbon, resulting in a lower carbon in 5-year poplars but a higher in 11-year poplars compared to M. sacchariflorus. Therefore, the changes of soil properties in poplar plantation would have further effects on wetland ecosystems.