Activity and abundance of nitrous oxide consuming bacteria in Platismatia glauca cryptogamic lichen in boreal Finnish spruce forest.

The boreal spruce forest soil can assimilate atmospheric N2O through symbiotic relationships with mycorrhizae or with bacteria, especially during spring and autumn, when aerobic microsites to soil can form. In cold soils with large field capacity (FCD), high humidity and absence of fertilisation, a balance between absorption and emission of nitrous oxide and dinitrogen was observed to be close to zero, and even to assume negative values in some cases, thus suggesting that forest soils absorb more N2O than they emit. Furthermore, in the presence of cryptogamic coverings of mosses and lichens, the absorption value was observed to be greater than in forests with less coverage; although the main role in N2O absorption is played by soil and root system. However, the role played by epiphytic organisms in N2O absorption in the boreal forests has not been uncovered yet. We studied, N2O dynamics of the lichen, Platismatia glauca, showing that N2O is consumed especially at lower incubation temperatures. The quantitative analysis with real-time PCR of nitrous oxide reductase gene fragment nosZ, showed that enzyme is present in the lichen and the gene is more transcribed under lower incubation temperature. The presented results unveil that cryptogamic covers consume nitrous oxide (with values between 0.1 and 0.4 ng N2O-C/g (ww)/h) at the atmospheric concentration via complete dissimilatory denitrification when nitrogen is limited.