Tree Species Effects on Potential Production and Consumption of Carbon Dioxide, Methane, and Nitrous Oxide: The Siberian Afforestation Experiment

Abstract

Changes in tree species composition could affect how forests produce and consume greenhouse gases, because the soil microorganisms that carry out these biogeochemical transformations are often sensitive to plant characteristics. We examined the effects of thirty years of stand development under six tree species in Siberian forests (Scots pine, spruce, arolla pine, larch, aspen and birch) on potential rates of soil CO₂ production, N₂O-reduction and N₂O production during denitrification, and CH₄ oxidation. Because many of these activities relate to soil N turnover, we also measured net nitrification and N mineralization. Overall, the effects of tree species were more pronounced on N₂O and CH₄ fluxes than on CO₂ production. Tree species altered substrate-induced respiration (SIR) and basal respiration, but the differences were not as large as those observed for N transformations. Tree species caused similar effects on denitrification potential, net N mineralization, and net nitrification, but effects on N₂O reduction were idiosyncratic, resulting in a decoupling of N₂O production and reduction. CH₄ oxidation was affected by tree species, but these effects depended on soil moisture: increasing soil moisture enhanced CH₄ oxidation under some tree species but decreased it under others. If global warming causes deciduous species to replace coniferous species, our results suggest that Siberian forests would support soil microbial communities with enhanced potential to consume CH₄ but also to produce more N₂O. Future predictions of CH₄ uptake and N₂O efflux in boreal and temperate forests need to consider changes in tree species composition together with changes in soil moisture regimes.