Effect of crustose lichen (Ochrolecia frigida) on soil CO₂ efflux in a sphagnum moss community over western Alaska tundra

Abstract. Soil CO₂ efflux-measurements represent an important component for estimating an annual carbon budget in response to changes in increasing air temperature, degradation of permafrost, and snow-covered extents in the Subarctic and Arctic. However, it is not widely known what is the effect of curstose lichen (Ochrolecia frigida) infected sphagnum moss on soil CO₂ emission, despite the significant ecological function of sphagnum, and how lichen gradually causes the withering to death of intact sphagnum moss. Here, continuous soil CO₂ efflux measurements by a forced diffusion (FD) chamber were investigated for intact and crustose lichen sphagnum moss covering over a tundra ecosystem of western Alaska during the growing seasons of 2015 and 2016. We found that CO₂ efflux in crustose lichen during the growing season of 2016 was 14 % higher than in healthy sphagnum moss community, suggesting that temperature and soil moisture are invaluable drivers for stimulating soil CO₂ efflux, regardless of the restraining functions of soil moisture over emitting soil carbon. Soil moisture does not influence soil CO₂ emission in crustose lichen, reflecting a limit of ecological and thermal functions relative to intact sphagnum moss. During the growing season of 2015, there is no significant difference between soil CO₂ effluxes in intact and crustose lichen sphagnum moss patches, based on a one-way ANOVA at the 95 % confidence level (p < 0.05). Considering annual soil CO₂ effluxes simulated by temperature, as well as monitoring of snow depth by time-lapsed camera, average snow-covered and snow-free CO₂ contributions to annual carbon budgets correspond to 28.4 % and 71.6 % in intact sphagnum moss cover, and 25.0 % and 75.0 % in a crustose lichen sphagnum moss colony, respectively. Therefore our findings demonstrate that soil CO₂ emissions in the crustose lichen-infected sphagnum moss community would be steadily stimulated by a widespread outbreak of airborne plants over intact sphagnum moss, and by a rapid degradation of permafrost in response to drastic changes in climate and environment in the Subarctic and Arctic.