Restoration of methane oxidation abilities of desiccated paddy soils after re-watering

Restoration of CH4-oxidation activities of desiccated paddy soils and the NH4+ effect after watering were investigated in laboratory incubations. Fresh paddy soil collected from an intermittently flooded rice field in Wuxi, Jiangsu province, showed a parabolic relationship between CH4-oxidation activity and soil moisture with an optimum CH4-oxidation rate at 71% water-holding capacity (WHC), while the paddy soil collected from a permanently flooded rice field in Yingtan, Jiangxi province, showed a much smaller CH4-oxidation ability, which increased exponentially with soil moisture increasing from 28% WHC to 95% WHC at an initial CH4 concentration of approximately 2,200 microliter l-1 and at room temperature (25 degrees C). CH4-oxidation ability was inversely related to N2O emission and related positively with CO2 emission in response to the change in soil moisture. Desiccated paddy soils lost their CH4-oxidation abilities. However, this was recovered after the soils were re-watered. The restoration of CH4-oxidation ability was directly dependent upon soil moisture and the rate of its restoration increased with increasing soil moisture content from 40% to 90% WHC. Addition of NH4Cl at rates of 0-3.57 micromol g-1 soil inhibited the restoration of CH4-oxidation ability significantly (P<0.01), but the inhibitory effect was alleviated by a high soil moisture content. The restoration of CH4-oxidation ability was much slower in the Yingtan soil than in the Wuxi soil. The studies show that the optimum moisture content of paddy soils for CH4 oxidation depends on the methanotrophic bacteria in relation to the prevailing water regime; desiccation damages the CH4-oxidation ability of permanently flooded paddy soil more severely than that of frequently well-drained soils.