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