Influence of soil temperature on methane emission from rice paddy fields

Abstract

Methane emission rates from an Italian rice paddy field showed diel and seasonal variations. The seasonal variations were not closely related to soil temperatures. However, the dieL changes of CH₄ fluxes were significantly correlated with the diel changes of the temperature in a particular soil depth. The soil depths with the best correlations between CH4 flux and temperature were shallow (1–5cm) in May and June, deep (10–15cm) in June and July, and again shallow (1–5 cm) in August. Apparent activation energies (E_a) calculated from these correlations using the Arrhenius model were relatively low (50–150 kJ mol⁻¹) in May and June, but increased to higher values (80–450 kJ mol⁻¹) in August. In the laboratory, CH₄ emission from two rice cultures incubated at temperatures between 20 and 38°C showed E _α. values of 41 and 53 kJ mol⁻¹) Methane production in anoxic paddy soil suspensions incubated between 7 and 43°C showed E _α values between 53 and 132 kJ mol⁻¹ with an average value of 85 kJ mol⁻¹) and in pure cultures of hydrogenotrophic methanogenic bacteria E _a values between 77 and 173 (average 126) kJ mol⁻¹. It is suggested that diel changes of soil properties other than temperature affect CH₄ emission rates, e.g. diel changes in root exudation or in efficiency of CH⁴ oxidation in the rhizosphere.