Impact of mosses and lichens on future carbon emissions from permafrost soils

Mosses and lichens may play an important role for the future release of carbon from permafrost soils in high-latitude ecosystems. They significantly increase ecosystem carbon sequestration through productivity, and they also reduce soil temperature through insulation, thereby preventing permafrost carbon from being emitted as CO2. However, quantitative, large-scale estimates of the contribution of mosses and lichens to the future state of soil carbon at high latitudes are rare so far. Here, we use a processed-based model of mosses and lichens, which is integrated into a global land surface model, to predict the overall effect of these organisms on the soil carbon balance. We find that mosses and lichens double the increase in total soil carbon by the year 2100 compared to a simulation without the organisms, which can be explained by two factors: First, the cooling effect of mosses and lichens on soil temperature increases by around 1 degree C from today to 2100. Secondly, increased productivity of mosses and lichens due to CO2-fertilisation results in a larger carbon flux into the soil. Hence, we predict that mosses and lichens will contribute substantially to the future carbon balance of northern ecosystems and should not be neglected in simulations of the future carbon cycle.