Accelerated foliar litter humification in forest gaps: Dual feedbacks of carbon sequestration during winter and the growing season in an alpine forest

Abstract

Can forest gaps lead to constrained litter decomposability by redistributing heat and moisture conditions, thereby increasing carbon sequestration from plant to soil via litter humification in alpine forests? We studied mass losses, humic substances, humic acid, fulvic acids, as well humification degrees and humification ratios in six foliar litters with a field litterbag experiment from the gap center, canopy gap and expanded gap to the closed canopy in winter and the growing season in an alpine forest of the east Tibetan Plateau. Humification degrees of 18%–45% for birch, 15%–40% for fir, 8%–30% for willow, 14%–26% for cypress, 9%–25% for larch and 7%–19% for azalea foliar litter were observed in forest gaps and the closed canopy over one year of incubation. Small amounts of humic substances accumulated in winter, whereas considerable humic acid accumulated, but fulvic acid mineralized during the growing season. Compared with the closed canopy, foliar litter humification in forest gaps was lower in winter but greater in the growing season, implying a dual role of forest gaps in carbon sequestration between winter and the growing season. Carbon sequestration could be accelerated in forest gaps. Reduced snow cover under a scenario of winter warming would stimulate soil carbon storage in these alpine forests.