Abstract: Soluble carbon during foliar litter decomposition in alpine forests plays an important role in carbon cycling in ecosystems, which is also closely related to the material and energy flow in downstream ecosystems. However, forest gaps could regulate soluble carbon dynamics during litter decomposition by changing the frequency of soil freeze-thaw cycles in winter and hydrothermal environment in growing seasons, but little information has been available. Therefore, a field litterbag experiment was conduct in an alpine forest in western Sichuan Province, China from 15 November 2012 to 31 October 2013. Foliar litter of typical arbor species (birch: Betula albo-sinensis, cypress: Sabina saltuaria, larch: Larix mastersiana and fir: Abies faxoniana) and shrub species (willow: Salix paraplesia, azalea: Rhododendron lapponicum) were selected. Samples of air-dried foliar litter were filled in nylon litterbags and placed on the forest floor with 2 cm spacing between litterbags from the gap center, canopy gap edge, extended gap edge to closed canopy in the alpine forest. The litterbags were sampled at snow formation stage, snow cover stage, snow melt stage and growing season in the first year of decomposition. The results indicated that the content of soluble carbon and soluble organic carbon from the foliar litter of the six species showed a similar dynamical tendency at the first year of litter decomposition. Both contents of soluble carbon and soluble organic carbon increased in winter, and decreased in growing season, though the content of soluble inorganic carbon decreased in the first year of litter decomposition. The maximum contents of soluble carbon and soluble organic carbon in closed canopy were observed at snow formation stage regardless of litter species, but those in gap center and extended gap edge were observed at snow cover stage. In contrast, the contents of soluble carbon, soluble organic carbon and soluble inorganic carbon decreased significantly in growing season, even less than the initial contents. Multivariate analysis displayed that the contents of soluble carbon and soluble inorganic carbon were significantly affected by forest gap in the first year of litter decomposition, but the content of soluble organic carbon only affected by forest gap in the winter. Moreover, the contents of soluble carbon and soluble organic carbon were influenced particularly by litter quality in the winter. These results suggested that the ongoing winter warming would decrease the content of soluble carbon during foliar litter decomposition by decreasing the cover-time and thickness of snow in the winter, although the decrease degree could be controlled by litter quality.

Key words: forest gap, alpine forest, soluble carbon, litter decomposition, snow cover