Soil CO2 efflux and production rates as influenced by evapotranspiration in a dry grassland

Aims: Our aim was to study the effect of potential biotic drivers, including evapotranspiration (ET) and gross primary production (GPP), on the soil CO2 production and efflux on the diel time scale. Methods: Eddy covariance, soil respiration and soil CO2 gradient systems were used to measure the CO2 and H2O fluxes in a dry, sandy grassland in Hungary. The contribution of CO2 production from three soil layers to plot-scale soil respiration was quantified. CO2 production and efflux residuals after subtracting the effects of the main abiotic and biotic drivers were analysed. Results: Soil CO2 production showed a strong negative correlation with ET rates with a time lag of 0.5h in the two upper layers, whereas less strong, but still significant time-lagged and positive correlations were found between GPP and soil CO2 production. Our results suggest a rapid negative response of soil CO2 production rates to transpiration changes, and a delayed positive response to GPP. Conclusions: We found evidence for a combined effect of soil temperature and transpiration that influenced the diel changes in soil CO2 production. A possible explanation for this pattern could be that a significant part of CO2 produced in the soil may be transported across soil layers via the xylem.