太湖流域上游西苕溪源头溪流中毛竹、石栎和山胡椒落叶分解比较

Leaf litter breakdown of Phyllostachys heterocycla,Lithocarpus glabra and Lindera glauca in a headwater stream of Xitiaoxi watershed,upper reaches of Taihu Basin,China

比较了毛竹、石栎和山胡椒叶片的理化属性,采用粗网叶袋法研究了三种落叶在太湖流域上游西苕溪中的分解过程,探讨了毛竹叶成为溪流优势外来能源后对溪流生态过程和底栖动物群落结构的影响.三种落叶的氮、磷含量及叶片厚度都存在显著差异,毛竹叶的氮含量(30.23 g/kg)远高于石栎(20.98 g/kg)和山胡椒(9.69 g/kg),其中毛竹叶的分解速率最快(k=0.00592 d-1),山胡椒(0.00297 d-1)和石栎叶(0.00212 d-1)较慢.三种落叶叶袋间的大型底栖无脊椎动物包括各取食功能团的多度和生物量无显著差异,而4次采样间的差异很显著.大型底栖动物的取食功能团中,撕食者的数量比例最高(40.3%),生物量比例为41.6%,是落叶分解的重要功能类群.撕食者中,利用阔叶筑巢的鳞石蛾Lepi-dostoma数量最多,占全部底栖动物的14%,是该溪流中主要的撕食者类群.因此,由于毛竹叶具有氮、磷含量较高、叶形较窄,以及两年进行一次换叶的特点,当毛竹叶替代其他阔叶秋季落叶的树种成为源头溪流优势外来能源后,可能会改变源头溪流中的氮磷含量、溪流外来能源的量和滞留时间以及底栖动物群落结构.

In order to explore the impact of the change of the dominant leaf litter source in stream from broad leaf trees to a bamboo tree of Phyllostachys heterocycla on headwater stream ecosystem and their associated benthic macroinvertebrates, we compared the leaf physical and chemical characters of Phyllostachys heterocycla, Lithocarpus glabra and Linderu glauca, and then evaluated the leaf litter breakdown of above three species using coarse-mesh litter bags in a headwater stream of Xitiaoxi watershed, Zhejiang Province. The concentrations of nitrogen , phosphorus and the thickness of the three categories of leaves varied significantly. The nitrogen concentration of bamboo tree leaf （30.23 g/kg） was much higher than that of L. glabra （20：98 g/kg） and L. glauca （ 9.69 g/kg）. Moreover, the leaves of P. heterocycla （ k = 0.00592 d - 1 ） decomposed faster than those of L. glabra （ O. 00297 d - l ） and L. glauca （0. 00212 d- 1 ）. No significant differences were observed in macroinvertebrates abundance and biomass among the three leaf types, however, the macroinvertebrate abundance and biomass varied significantly during the sampling period. Propor- tions of the functional feeding groups showed that shredders was the most abundant group, which represented 40.3% of individuals and 41.6% of the macroinvertebrate biomass, indicating it was an important component of fauna associated with litter breakdown. The dominant shredder taxon is Lepidostoma, which constructs nests based on broadleaves, and accounts for 14% of the total mac- roinvertebrate individuals. Because bamboo leaves are narrower, with higher concentrations of nitrogen and phosphorus, and defoli- ation occurs every two years. We concluded that when the leaf litter source of headwater streams dominated by bamboo leaf, it might change the concentrations of nitrogen and phosphorus in the stream water, the annual amount of leaf litter into stream, the retention time, and the macrobenthos community structure.