Forest gaps retard carbon and nutrient release from twig litter in alpine forest ecosystems

Changes in soil microclimate driven by forest gaps have accelerated mass loss and carbon (C), nitrogen (N) and phosphorus (P) release from foliar litter in alpine forests ecosystems. Yet, it is unclear whether the same gap effect occurs in twig litter decomposition. A 4-year decomposition experiment was conducted in an alpine forest to explore the litter mass loss and C, N and P release among four gap treatments, including (1) closed canopy, (2) small gap (< 10 m in diameter), (3) middle gap (10-15 m in diameter) and (4) large gap (15-20 m in diameter). Compared to the closed canopy, thicker snow cover within gaps resulted in higher soil temperatures but lower frequency of the freeze-thaw cycles during winter. Moreover, gaps slowed the decay rate and C, N and P release after 4-year decomposition, and a total 31-62% of mass, 42-91% of C, 21-111% of N and all P were lost across gaps in winter. Statistical analysis indicated that gap-caused changes in soil temperature and freeze-thaw cycle had significant effects on C, N and P release of twig litter. This study highlights the importance of winter decomposition and gap-driven process in alpine forest ecosystems in southwestern China.