Temperature controls on diurnal carbon dioxide flux: Implications for estimating soil carbon loss

Carbon dioxide flux from the soil to the atmosphere is an important component of terrestrial C cycling, and accurate estimates of CO2-C fluxes are critical in estimating C budgets. Accurate estimation of daily C loss from infrequent measurements of CO2 flux requires characterization of the temporal variability associated with this processes. We investigated the relationships between diurnal CO2 flux and temperature at two locations, corresponding to two soil types (a sandy loam and a clay loam) in a residue covered no-till corn (Zea mays L.)/soybean field (Glycine Max. L. Merr.). Automated chambers provided hourly measurements of CO2 flux from 4 Mar. through 6 June 2000. Hourly soil temperature measurements were made at the surface and at the 0.05-m depth, along with air temperature and soil water content measurements. Time series analysis showed that the temporal dynamics of CO2 flux were more closely related to air temperature than to soil temperature, perhaps because a substantial portion of the CO2 originated from surface residues. Exponential temperature correction algorithms (Q(10)) were evaluated using a range of Q(10) factors applied to both air and soil temperatures. We found that a Q(10)=2 relationship when applied to a 0.05-m soil temperature performed poorly in this regard, however, air temperature based Q(10) relationships (Q(10)=1.5 or 1.25) performed better in that they reduced time-of-day estimation biases from 28 to <4%. Knowledge of the efficacy of temperature correction algorithms and application of the appropriate temperature measurements should improve the accuracy of cumulative C flux estimates from short-term measurements.