Effects of tree species composition on the CO2 and N2O efflux of a Mediterranean mountain forest soil

Abstract

Tree species composition shifts can alter soil CO2 and N2O effluxes. We quantified the soil CO2 and N2O efflux rates and temperature sensitivity from Pyrenean oak, Scots pine and mixed stands in Central Spain to assess the effects of a potential expansion of oak forests. Soil CO2 and N2O effluxes were measured from topsoil samples by lab incubation from 5 to 25 °C. Soil microbial biomass and community composition were assessed. Pine stands showed highest soil CO2 efflux, followed by mixed and oak forests (up to 277, 245 and 145 mg CO2-C m−2 h−1, respectively). Despite contrasting soil microbial community composition (more fungi and less actinomycetes in pine plots), carbon decomposability and temperature sensitivity of the soil CO2 efflux remain constant among tree species. Soil N2O efflux rates and its temperature sensitivity was markedly higher in oak stands than in pine stands (70 vs. 27 μg N2O-N m−2 h−1, Q10, 4.5 vs. 2.5). Conversion of pine to oak forests in the region will likely decrease soil CO2 effluxes due to decreasing SOC contents on the long run and will likely enhance soil N2O effluxes. Our results present only a seasonal snapshot and need to be confirmed in the field.