Diurnal deviations in the relationship between CO2 efflux and temperature: A case study

• Influence of time of day of CO2 measurements on estimation of the released C amount.
• The lowest bias of amount of released C from soil was around 10am and 8pm.
• The study suggests improvements of manual measurements of soil CO2 efflux.

Manual measurements of soil CO2 efflux and continuously measured soil temperature can be used to model seasonal sums of carbon released from soil. The aims of this study were i) to determine differences in soil CO2 efflux and temperature measured at different times of day and night, ii) to assess how can the time of soil CO2 measurements bias the parameter of temperature sensitivity (Q10) of CO2 efflux, and iii) to compare seasonal sum of carbon released from soil as calculated from continuous measurement and from models based on measurements at different times. We subsampled continuous measurements of soil CO2 efflux and soil temperature according to the time of day when the measurements were made and these data sets were analysed. We found that different Q10 values were significantly different for each individual data set. Estimation of the total seasonal amount of released soil carbon based on models of individual data sets differed by as much as 7.2% from continuously measured data. The smallest difference between modelled and continuously measured CO2 efflux was observed at 20:00 and the highest at 04:00. The study shows that the times at which manual measurements are taken should be considered in the subsequent data processing.