岷江上游高山森林冬季河流中凋落叶碳、氮和磷元素动态特征

Carbon, nitrogen and phosphorus dynamics during winter foliar litter decomposition in an alpine forest river in the upper reaches of the Minjiang River

高山森林河流中凋落叶元素释放动态不仅是生态系统物质循环和能量流动的重要组成部分,而且是森林养分流失的主要过程,并可能与冬季雪被和冻融导致的水环境变化密切相关.以岷江上游高山森林4种代表性植物康定柳(Salix paraplesia)、高山杜鹃(Rhododendron lapponicum)、方枝柏(Sabina saltuaria)和四川红杉(Larix mastersiana)凋落叶为对象,采用凋落叶分解袋法,研究冬季不同冻融时期(冻结初期、冻结期、融化期)河流中凋落叶碳(C)、氮(N)和磷(P)元素动态特征.康定柳、方枝柏和四川红杉凋落叶C(14.6%-47.7%)、N(22.3%-58.5%)和P(4.8%-20.5%)元素在整个冬季均表现为明显的释放现象,而高山杜鹃凋落叶C(-7.3%)和N(-62.7%)表现为明显的负释放(富集)现象,P(0.7%)表现为微量的释放现象.整体而言,凋落叶分解过程中C、N和P元素在冬季的冻结初期、冻结期和融化期整体表现为释放—富集—释放的模式,但康定柳和方枝柏凋落叶N表现为富集—富集—释放模式,方枝柏凋落叶P表现为释放—富集—富集模式.同时,凋落叶C、N和P元素的释放率受河流水温、p H、电导率和C、N、P营养元素等水体环境因子的显著影响.这些结果表明高山森林河流水环境特征显著影响了凋落叶分解过程中元素动态及其相关的物质循环过程,但影响程度受到凋落叶种类和基质质量的控制.

Nutrient dynamics during litter decomposition in rivers is not only an important part of material circulation andenergy flow in alpine forest ecosystems, but also closely related to forest nutrient output and downstream aquatic environments. This process can be affected by changes of snow cover and soil freeze-thaw cycles in the alpine forest. This study used litter bag method to investigate the carbon （C）, nitrogen （N） and phosphorus （P） dynamics during foliar litter decomposition of four dominate plants Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana in different periods of winter （we-freezing, freezing, and thawing） in an alpine forest river in the upper reaches of Minjiang River. The results showed obvious release patterns of C （14.6-47.7%）, N （22.3-58.5%） and P （4.8-20.5%） from S. paraplesia, S. saltuaria, and L. rnastersiana foliar litter throughout the winter. But C （-7.3%） and N （-62.7%） of R. lapponicum foliar litter displayed accumulation patterns and P （0.7%） a tiny release pattern. As a whole, the concentrations of C, N and P showed a pattern of release -- accumulation -- release in the decomposition procedures during the pre-freezing, freezing, and thawing periods. However, the difference of release magnitude was observed among different periods and different litter species. Meanwhile, other water physicochemical characteristics in river, e.g. pH, conductivity, and N and P nutrient availability, were shown to be related to the release rate of C, N, and P significantly. All the results suggested that alpine forest river water characteristics have significant impacts on nutrients dynamics and related processes of material cycles during litter decomposition, but themagnitude could be controlled by the litter quality.