title: Effects of increased CO2and N on CH4efflux from a boreal mire: a growth chamber experiment.
abstract: Increases in the supply of atmospheric CO2and N are expected to alter the carbon cycle, including CH4emissions, in boreal peatlands. These effects were studied in a glasshouse experiment with peat monoliths cored from an oligotrophic pine fen. The cores with living plants were kept in 720 ppmvand 360 ppmvCO2atmospheres for about 6 months under imitated natural temperature cycle. Fertilisation with NH4NO3(3 g m-2for 25 weeks) was applied to 18 of the 36 monoliths. The rate of CH4flux was non-linearly dependent on the number of Eriophorum vaginatum shoots growing in the monoliths, probably due to the gas transport properties of the aerenchyma. The average CH4efflux rate, standardised by the number of shoots, was increased by a maximum of 10-20% in response to the raised CO2level. In the raised-NH4NO3treatment, the increase in CH4release was lower. The effect of combined CO2+NH4NO3on CH4release was negligible and even lower than in the single treatments. Both potential CH4production and oxidation rates at 5, 15 and 25°C were higher near the surface than at the bottom of the core. As expected, the rates clearly depended on the incubation temperature, but the different treatments did not cause any consistent differences in either CH4production or oxidation. The determination of potential CH4production and oxidation in the laboratory is evidently too crude a method of differentiating substrate-induced differences in CH4production and oxidation in vivo. These results indicate that an increase in atmospheric CO2or N supply alone, at least in the short term, slightly enhances CH4effluxes from boreal peatlands; but together their effect may even be restrictive.
authors.affiliation: Department of Biology, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland e-mail: sanna.saarnio@joensuu.fi, Tel.: +358-13-251111, Fax: +358-13-2513590, , , , , , FI.
authors.forename: S
authors.initials: S
authors.lastname: Saarnio
authors.affiliation: Department of Biology, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland e-mail: sanna.saarnio@joensuu.fi, Tel.: +358-13-251111, Fax: +358-13-2513590, , , , , , FI.
authors.forename: J
authors.initials: J
authors.lastname: Silvola
keywords: CH4; CO2 and NH4NO3 fertilisation; Key words Atmospheric change; Shoot density