A mesocosm study on carbon transfer mechanisms from deadwood to litter through fungal hyphal growth

Hyphae-forming fungi play a critical role in decomposing deadwood and plant litter, utilizing a variety of resources in forest ecosystems. While the redistribution of nitrogen and phosphorus by fungal hyphae between deadwood and soil has been established, the translocation of carbon (C) and its subsequent utilization remains unexplored. This study examines the fungal-mediated transfer of ¹³C-cellulose from deadwood of European beech and Norway spruce to Norway spruce litter from an Oi/Oe horizon. We used a mesocosm double-chamber controlled system with a perforated intersection, including beech and spruce deadwoods (chamber I) and spruce litter (chamber II). After fungal hyphae growth in the intersection between the two chambers, mesocosms were incubated for 8–10 weeks at 20 °C in the dark. Following a pre-treatment phase, ¹³C-cellulose was added to half of the deadwood chambers while the other half served as control without cellulose addition. The transfer of ¹³C-cellulose from deadwood to spruce litter was assessed by measuring the abundance of ¹³C in respiration and microbial biomass within the spruce litter. After incubation, the ¹³C-cellulose recovered in spruce litter was higher for both respiration (7.75 ± 0.98 %) and microbial biomass (1.66 ± 1.01 %) for beech compared to the spruce deadwood (3.88 ± 1.07 % in respiration and 1.55 ± 1.37 % in microbial biomass). This indicates that, in both deadwood setups, more ¹³C was recovered in respiration than in microbial biomass. Molecular analysis of the fungal hyphae at the intersection between the deadwood and spruce litter chambers identified Clitopilus baronii and Kuehneromyces mutabilis as the common and active deadwood-decaying fungi facilitating significant ¹³C transfer (240–270 δ‰ in respiration, and 100–160 δ‰ in MBC), while the baseline without ¹³C was −25 δ‰. This research provides new insights into the mechanisms of C transfer from deadwood to litter, suggesting an enhanced decomposition of litter by deadwood decaying fungi.