In vitro decomposition of Sphagnum-derived acrotelm and mesotelm peat by indigenous and alien basidiomycetous fungi

Northern peatlands have accumulated significant quantities of peat, and it has been predicted that rates of peat decomposition may increase due to climate warming. In peatlands, organic matter decomposition in the acrotelm is accomplished primarily by fungi that act differentially through time on various peat constituents. After four months of decomposition in vitro, I show a distinct microbiological limitation to the decomposition of Sphagnum-derived peat (mean mass losses of 1.1–7.1 %) by indigenous and alien basidiomycetous fungi of both acrotelm and mesotelm peat (the mesotelm is the lower part of the acrotelm sensu lato, in which conditions fluctuate between oxic and anoxic). Neither acrotelm nor mesotelm Sphagnum peat can be degraded effectively by many fungi (mean mass losses of 2.7 % and 4.3 % for acrotelm and mesotelm peat, respectively), including the ubiquitous wood decomposing basidiomycetes known to decompose some of nature’s most complex polymers. Peatland basidiomycetes caused significantly greater mass losses of acrotelm and mesotelm peat than wood decay basidiomycetes (mean mass losses of 5.7 % and 1.4 %, respectively). Brown rot fungi caused significantly greater mass losses to acrotelm and mesotelm peat than white rot fungi and non-wood-decay fungi (mean mass losses of 10.1 %, 1.7 %, and 2.3 %, respectively). Rates of peat decomposition may not increase to the extent previously predicted, and peatlands may not necessarily be long-term sources of CO2 in response to a warming climate.