川西亚高山/高山森林土壤养分动态及其对季节性冻融的响应

Seasonal freeze-thaw in the subalpine/alpine region is a common climate phenomenon. In order to understand soil nutrients dynamics and their responses to seasonal freeze-thaw cycle in the subalpine/alpine forests of western Sichuan, three fir (Abies faxoniana) forests, including primary fir forest at 3582 m of altitude, fir and birch mixed forest at 3298 m of altitude, and secondary fir forest at 3023 m of altitude, were selected covering a 600 m vertical transition zone. Soils were sampled in different stages as the onset of soil freezing period, soil frozen period, soil thawing period and growing period from November 2008 to October 2009. The dissolve carbon and nitrogen, NH4+-N and NO3--N were measured. Soils in the sampled forests had relatively high dissolve carbon and nitrogen, NH4+-N and NO3--N in winter. The dynamics of measured soil nutrients changed with the process of soil freeze-thaw. In the soil organic layer, the dissolve carbon and nitrogen, NH4+-N and NO3--N experienced a significantly increasing then decrease dynamics in both the onset of soil freezing period and soil thawing period, and these measured nutrients showed little change in soil frozen period except that NH4+-N obviously increasing. In the mineral soil layer, the dissolve carbon and nitrogen, NH4+-N and NO3--N also experienced a significantly increasing then decrease dynamics in onset of soil freezing period. However, the dissolve nitrogen, NH4+-N and NO3--N obviously increased n soil frozen period, and these investigated soil nutrients reached to an obvious peak in soil thawing period. The results suggested that seasonal freeze-thaw is crucial stage for soil ecological processes, and soil freeze-thaw pattern significantly influenced the processes of soil nutrients.