Abstract: Soil nitrogen mineralization is a key component of nutrient cycling in forest ecosystems. The variations of winter snow cover in alpine forests, driven by global climate warming, can significantly affect soil nitrogen mineralization by altering surface micro-environmental conditions. In this study, we conducted an in-situ experiment that compared natural snow input (control) and snow removal treatment in a subalpine Abies faxoniana forest in western Sichuan. We investigated the effects of snow removal on soil micro-environmental conditions, organic and inorganic nitrogen contents, and nitrogen mineralization rates. The results showed that snow removal significantly increased the frequency of freeze-thaw cycles in the soil organic layer and reduced the water content in the soil organic layer and mineral soil layer by 11.86% and 16.24%, respectively. It also induced marked temperature fluctuations in the organic layer during winter and notably decreased soil temperature during the growing season. Snow removal resulted in significant increases in total nitrogen (TN), microbial biomass nitrogen (MBN), and dissolved organic nitrogen (DON) in the soil organic layer by 96.23%, 82.72%, and 210.96%, respectively. In contrast, TN and MBN contents in the mineral soil layer decreased by 9.73% and 64.97%, respectively. Moreover, snow removal enhanced net nitrogen mineralization rates by 248.27% in the organic layer and by 4.94% in the mineral layer. These effects suggest that snow removal affects soil nitrogen mineralization process in the organic layer by altering soil temperature and regulating the transformation of organic nitrogen to inorganic nitrogen. However, in the mineral layer, soil nitrogen mineralization is primarily promoted by increased organic nitrogen input. In summary, snow cover changes influence nitrogen mineralization in subalpine forest soils by modulating both temperature regimes and substrate availability. These findings contribute to a better understanding of how subalpine forest ecosystem processes respond to global climate change.

Key words: snow cover, freeze-thaw, nitrogen, nitrogen mineralization, subalpine