OOS 7-2 - The consistent temperature dependence of wood carbon fluxes across nutrient gradients

The flux of CO2 from wood decomposition is a fundamental component of the global carbon cycle, but the impact of human-induced changes in temperature and nutrients on this flux is not well understood. We examined the effects of nitrogen and phosphorous addition on the temperature-dependence of CO2 fluxes from wood with differing traits (angiosperm and gymnosperm) over a three-year period. Results showed that CO2 fluxes were driven primarily by phosphorus and only secondarily by nitrogen, and that the effect of phosphorus was mediated by wood traits, with a greater increase in gymnosperms than angiosperms. P addition had positive effects on fungal  diversity and Ascomycota:Basidiomycota ratio in angiosperms, and Ascomycota:Basidiomycota ratio positively influenced CO2 flux. In contrast, these effects were negative in gymnosperms. The temperature dependences of CO2 fluxes were remarkably constant across nutrient levels, consistent with metabolic scaling theory hypotheses. These results suggest that phosphorus availability is a key driver of variation in wood CO2 fluxes, but has a limited impact on the temperature dependence. Our findings can inform predictions for wood carbon fluxes in a changing climate.