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Summer droughts projected to increase in central Europe due to climate changes strongly influence the carbon cycle of ecosystems. Persistent respiration activities during drought periods are responsible for a significant carbon loss, which may turn the ecosystem from a sink into a source of carbon. There are still gaps in our knowledge regarding the characteristic changes taking place in the respiration of the different components of the ecosystem in response to drought events. In the present study, we combined a physical separation of soil respiration components with continuous measurements of soil CO2 efflux and its isotopic (13C) signals at a dry grassland site in Hungary. The physical separation of soil respiration components was performed by means of inox meshes and tubes inserted into the soil. The root-excluded and root- and mycorrhiza-excluded treatments served to measure the isotopic signals of the rhizospheric, mycorrhizal fungi and heterotrophic components, respectively. In the dry grassland investigated in the study the three components of the soil CO2 efflux decreased at different rates under drought conditions. During drought the contribution made by the heterotrophic components was the highest (54±8%; mean ±SE). Rhizospheric component was the most sensitive to soil drying with its relative contribution to the total soil respiration dropping from 66±7 (non-stressed) to 35±17% (mean ±SE) under drought conditions. According to our results the heterotrophic component of soil respiration is the major contributor to the respiration activities during drought events in the dry grassland ecosystem studied, Biogeosciences Discussions, 12, ISSN:1810-6277, ISSN:1810-6285

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 0.5 h 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., Plant and Soil, 388 (1-2), ISSN:0032-079X, ISSN:1573-5036