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Aims: Our aim was to study the effect of potential biotic drivers, including evapotranspiration (ET) and gross primary production (GPP), on the soil CO production and efflux on the diel time scale. Methods: Eddy covariance, soil respiration and soil CO gradient systems were used to measure the CO and HO fluxes in a dry, sandy grassland in Hungary. The contribution of CO production from three soil layers to plot-scale soil respiration was quantified. CO production and efflux residuals after subtracting the effects of the main abiotic and biotic drivers were analysed. Results: Soil CO 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 CO production. Our results suggest a rapid negative response of soil CO 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 CO production. A possible explanation for this pattern could be that a significant part of CO produced in the soil may be transported across soil layers via the xylem. [ABSTRACT FROM AUTHOR]

Aims: Soil respiration (Rs) is a complex process including a wide range of soil biota and pathways of carbon cycling, all being under the control of various drivers. The most important biotic driver is the photosynthetic activity of the vegetation providing supply mainly for the autotrophic component of Rs: roots and their symbiotic partners. The objective of this study was to describe the time-lagged relationship between gross primary production (GPP) and the mycorrhizal Rs component in order to determine the amount of carbon derived from GPP appearing as mycorrhizal respiration (Rmyc).Measurements of Rs were conducted in three treatments - (i) undisturbed, root and arbuscular mycorrhizal fungi (AMF)-included (Rs), (ii) root-excluded (Rhet+myc) and (iii) root- and AMF-excluded (Rhet) plots - for three consecutive years in a Central-Hungarian dry sandy grassland. GPP data were derived from eddy-covariance measurements, while an automated system was used for continuous measurements of Rs. We analysed the relationship between Rmyc and GPP by using cross-correlation and by fitting sine wave models on the diel datasets.GPP was found to be the main driver of Rmyc, responding with an average time lag of 18 h. The greatest lags were detected during periods characterized by minimal photosynthetic activity, while lags were the smallest during active periods.Based on the seasonal changes in the delay, we concluded that GPP and soil temperature had simultaneous effects on the diel pattern of CO2 emission of the different autotrophic components depending on the vegetation activity and environmental conditions.Methods: Soil respiration (Rs) is a complex process including a wide range of soil biota and pathways of carbon cycling, all being under the control of various drivers. The most important biotic driver is the photosynthetic activity of the vegetation providing supply mainly for the autotrophic component of Rs: roots and their symbiotic partners. The objective of this study was to describe the time-lagged relationship between gross primary production (GPP) and the mycorrhizal Rs component in order to determine the amount of carbon derived from GPP appearing as mycorrhizal respiration (Rmyc).Measurements of Rs were conducted in three treatments - (i) undisturbed, root and arbuscular mycorrhizal fungi (AMF)-included (Rs), (ii) root-excluded (Rhet+myc) and (iii) root- and AMF-excluded (Rhet) plots - for three consecutive years in a Central-Hungarian dry sandy grassland. GPP data were derived from eddy-covariance measurements, while an automated system was used for continuous measurements of Rs. We analysed the relationship between Rmyc and GPP by using cross-correlation and by fitting sine wave models on the diel datasets.GPP was found to be the main driver of Rmyc, responding with an average time lag of 18 h. The greatest lags were detected during periods characterized by minimal photosynthetic activity, while lags were the smallest during active periods.Based on the seasonal changes in the delay, we concluded that GPP and soil temperature had simultaneous effects on the diel pattern of CO2 emission of the different autotrophic components depending on the vegetation activity and environmental conditions.Results: Soil respiration (Rs) is a complex process including a wide range of soil biota and pathways of carbon cycling, all being under the control of various drivers. The most important biotic driver is the photosynthetic activity of the vegetation providing supply mainly for the autotrophic component of Rs: roots and their symbiotic partners. The objective of this study was to describe the time-lagged relationship between gross primary production (GPP) and the mycorrhizal Rs component in order to determine the amount of carbon derived from GPP appearing as mycorrhizal respiration (Rmyc).Measurements of Rs were conducted in three treatments - (i) undisturbed, root and arbuscular mycorrhizal fungi (AMF)-included (Rs), (ii) root-excluded (Rhet+myc) and (iii) root- and AMF-excluded (Rhet) plots - for three consecutive years in a Central-Hungarian dry sandy grassland. GPP data were derived from eddy-covariance measurements, while an automated system was used for continuous measurements of Rs. We analysed the relationship between Rmyc and GPP by using cross-correlation and by fitting sine wave models on the diel datasets.GPP was found to be the main driver of Rmyc, responding with an average time lag of 18 h. The greatest lags were detected during periods characterized by minimal photosynthetic activity, while lags were the smallest during active periods.Based on the seasonal changes in the delay, we concluded that GPP and soil temperature had simultaneous effects on the diel pattern of CO2 emission of the different autotrophic components depending on the vegetation activity and environmental conditions.Conclusion: Soil respiration (Rs) is a complex process including a wide range of soil biota and pathways of carbon cycling, all being under the control of various drivers. The most important biotic driver is the photosynthetic activity of the vegetation providing supply mainly for the autotrophic component of Rs: roots and their symbiotic partners. The objective of this study was to describe the time-lagged relationship between gross primary production (GPP) and the mycorrhizal Rs component in order to determine the amount of carbon derived from GPP appearing as mycorrhizal respiration (Rmyc).Measurements of Rs were conducted in three treatments - (i) undisturbed, root and arbuscular mycorrhizal fungi (AMF)-included (Rs), (ii) root-excluded (Rhet+myc) and (iii) root- and AMF-excluded (Rhet) plots - for three consecutive years in a Central-Hungarian dry sandy grassland. GPP data were derived from eddy-covariance measurements, while an automated system was used for continuous measurements of Rs. We analysed the relationship between Rmyc and GPP by using cross-correlation and by fitting sine wave models on the diel datasets.GPP was found to be the main driver of Rmyc, responding with an average time lag of 18 h. The greatest lags were detected during periods characterized by minimal photosynthetic activity, while lags were the smallest during active periods.Based on the seasonal changes in the delay, we concluded that GPP and soil temperature had simultaneous effects on the diel pattern of CO2 emission of the different autotrophic components depending on the vegetation activity and environmental conditions. [ABSTRACT FROM AUTHOR]