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

Background and Aims

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.

Methods

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.

Results

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).

Conclusions

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.