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The main objective of the present study was to determine the contributions of autotrophic and heterotrophic components to the total soil CO 2 efflux over three years with high-frequency data acquisition by means of automated measurements. Soil CO 2 efflux was measured continuously by using an automated open system of 10 soil respiration chambers in a sandy grassland in Hungary. Mesh-collar technique was applied to separate the components of the total respiration. Data were collected (1) in root-exclusion (Exr), (2) in root- and mycorrhiza exclusion (Exrm) and (3) in control plots (Exc, roots and mycorrhiza included). We fitted three different models to describe the dependence of total soil CO 2 efflux measured on the Exc (Rs), CO 2 efflux measured on Exr (R TR ) and CO 2 efflux measured on Exrm (R TRM ) on abiotic and biotic drivers. The best fitted model (based on AIC) was later on used in a simulation process. The contribution by rhizospheric respiration (simulated, R rhizo* ) was 36 ± 21%, the contribution by mycorrhizal respiration (simulated, R myc* ) to the total soil respiration was 9 ± 9% while the contribution by heterotrophic respiration (simulated, R het* ) was 55 ± 21% on average. Measured mycorrhizal respiration (R M ) responded to GPP with a time lag of 0–2 days in active period. Drought affected the autotrophic component of soil respiration the most intensively: raise of soil water content resulted in increase of R S by 175% while R TR and R TRM increased by 127% and 93%, respectively. The results highlight the fact that it would be useful to establish and apply separate models for each component. [ABSTRACT FROM AUTHOR]

Diel variability of soil respiration could be driven by several factors, but temperature and carbon allocation have the most significant effect on that. However, these two factors covariate on multiple time scales, therefore it is not easy to disentangle their effect.We measured CO2 efflux in undisturbed, root-excluded and root- and mycorrhizal fungi excluded plots and analyzed the diel variability and the responses to GPP in different phenological stages. We used sine wave models to describe the characteristics of diel variability and to estimate the temperature and GPP driven part of total soil respiration.Rhizospheric respiration peaked 8-12 hours after GPP peak, while mycorrhizal fungi respiration had a longer time lag of 13-20 hours. Results of isotopic measurements also showed similar pattern. Drought affected respiration rates as well as carbon allocation pattern; both the amount and the speed of carbon allocated to mycorrhizal fungi were reduced under drought.Based on these results we assume that the commonly used Q10 values does not always reflect the temperature response of soil CO2 efflux, but the propagated effect of the temperature and belowground carbon allocation and those share in soil respiration vary with phenological stages. [ABSTRACT FROM AUTHOR]