高山森林溪流冬季不同时期凋落物分解中水溶性氮和磷的动态特征

Soluble nitrogen and soluble phosphorus dynamics during foliar litter decomposition in winter in alpine forest streams

为了解高山森林溪流凋落物冬季分解过程中水溶性氮和磷的变化过程,采用凋落叶分解袋法,以川西高山森林典型乔木(四川红杉、方枝柏)和灌木(高山杜鹃、康定柳)凋落叶为研究对象,研究冬季不同时期(冻结初期、冻结期、融化期)溪流、河流、河岸带以及林下凋落叶水溶性氮和磷的动态特征.结果表明:经过一个冬季的分解,4种凋落物在不同生境下各时期的水溶性氮含量无显著变化.水溶性磷含量除林下外在其他生境均显著降低,表现出河流<溪流<河岸带<林下的规律.高山森林凋落叶分解过程中水溶性磷含量与平均温度、正积温、负积温和流速呈显著负相关,水溶性氮含量与正积温呈显著正相关,物种显著影响凋落物分解过程中水溶性氮和磷的含量.高山森林凋落物冬季分解过程中水溶性磷更易随河流和溪流等水体的流动而流失,而水溶性氮受冬季水环境的影响相对较小.

In order to understand the dynamic pattern of soluble nitrogen and soluble phosphorus in the headwater streams during the process of litter decomposition in winter, a field experiment using litterbag method was conducted in an alpine forest in Western Siehuan, China. The foliar litter of two dominant canopy trees （Sabina saltuaria, and Larix mastersiana） and two shrubs （Salix para- plesia and Rhododendron lapponicum） were selected. The litterbags were placed in a headwater stream, river, riparian zone and closed canopy, and sampled in different freezing-thawing periods of winter （ pre-freezing period, freezing period and thawing period）. The results indicated that the sol- uble nitrogen content of foliar litter showed little changes over a whole winter decomposition regard- less of species. In contrast, the soluble phosphorus content displayed the order as river 〈 stream 〈 riparian zone 〈 closed canopy, and showed a decrease tendency in stream, river and riparian, al- though little changes under closed canopy over a whole winter decomposition. Correlation analysis suggested that the dynamics of soluble phosphorus content significantly correlated to the average temperature, positive accumulated temperature, negative accumulated temperature and flow velocity during the decomposition in winter. The dynamics of soluble nitrogen content only exhibited signifi- cant correlations with positive accumulated temperature. Additionally, litter quality （species） also controlled the dynamics of soluble nitrogen and soluble phosphorus content as litter decomposition proceeded. The results implied that soluble phosphorus could be more liable to loss in streams and rivers during litter decomposition compared with soluble nitrogen, which could further provide some new ideas in understanding nitrogen and phosphorus cycling in this alpine forest.