Functional traits of bryophytes and their role in buffering the impacts of climate change-induced decline of snow cover on belowground carbon inputs in boreal forest ecosystem

Boreal forests serve as major soil carbon reservoirs. However, climate-induced snow decline increases freeze-thaw cycles, disrupting below-ground carbon processes such as root dynamics, microbial activity, and biomass accumulation. Mosses, particularly Sphagnum spp. and Pleurozium schreberi, dominate boreal forest floors and contribute to soil insulation and moisture retention. Despite their ecological importance, their role in buffering soil carbon dynamics under reduced snow cover remains poorly understood. This study examines the functional traits of these mosses and their ability to mitigate the effects of snow cover loss on root biomass composition, microbial activity, and microbial biomass. Thirty-six experimental plots of 1.5 m * 1.5m were established in three mature black spruce stands in Nord-du-Québec, with treatments varying in moss type, presence, and snow cover. Moss functional traits—including colony density, water absorption capacity, and nutrient content were measured in late spring. Fine root biomass and composition were assessed through manual separation of live and dead roots, while microbial biomass was quantified using the chloroform fumigation method. Bacterial and fungal communities were characterized by amplifying and sequencing the 16S rRNA gene and the ITS2 region, respectively. Sphagnum spp. colonies under snow were denser and had higher water absorption capacity compared to those without snow. In contrast, P. schreberi did not show a significant difference between snow treatments. Total root biomass was significantly lower in Sphagnum spp. without snow compared to with snow, while other treatments were not significantly different from each other. Although bacterial diversity remained consistent across treatments, community composition was changed. Specifically, Actinobacteria were abundant when snow was reduced in P. schreberi plots, and Acidobacteriota increased significantly in Sphagnum spp. plots with snow compared to no snow. Fungal diversity decreased significantly when snow was reduced from P. schreberi plots. Microbial biomass was stable in early summer but increased in Sphagnum spp. with snow by late summer. As climate change accelerates and snow cover diminishes, preserving moss-dominated forest floors, especially those dominated by Sphagnum spp. may be critical for maintaining below-ground carbon dynamics, enhancing microbial resilience, and supporting root vitality in boreal forests. These findings highlight the role of moss functional traits in promoting soil resilience and carbon retention under changing winter conditions in northern boreal forests.