Agricultural factors affecting methane oxidation in arable soil

摘要

CH4oxidation activity in a sandy soil (Ardoyen) and agricultural practices affecting this oxidation were studied under laboratory conditions. CH4oxidation in the soil proved to be a biological process. The instantaneous rate of CH4consumption was in the order of 800 μmol CH4kg−1day−1(13 mg CH4kg−1day−1) provided the soil was treated with ca. 4.0 mmol CH4kg−1soil. Upon repeated supplies of a higher dose of CH4, the oxidation was accelerated to a rate of at least 198 mg CH4kg−1day−1. Addition of the plant-growth promoting rhizopseudomonad strainsPseudomonas aeruginosa7NSK2 andPseudomonas fluorescensANP15 significantly decreased the CH4oxidation by 20 to 30 during a 5-day incubation. However, with further incubation this suppression was no longer detectable. Growing maize plants prevented the suppression of CH4oxidation. The numbers of methanotrophic bacteria and fungi increased significantly after the addition of CH4, but there were no significant shifts in the population of total bacteria and fluorescent pseudomonads. Drying and rewetting of soil for at least 1 day significantly reduced the activity of the indigenous methanotrophs. Upon rewetting, their activity was regained after a lag phase of about 3 days. The herbicide dichlorophenoxy acetic acid (2,4-D) had a strong negative effect on CH4oxidation. The application of 5 ppm increased the time for CH4removal; at concentrations above 25 ppm 2,4-D CH4−oxidizing activity was completely hampered. After 3 days of delay, only the treatments with below 25 ppm 2,4-D showed recovery of CH4−oxidizing activity. This finding suggests that it can be important to include a CH4−removal bioassay in ecotoxicology studies of the side effects of pesticides. Changes in the native soil pH also affected the CH4−oxidizing capacity. Permanent inhibition occurred when the soil pH was altered by 2 pH units, and partial inhibition by 1 pH unit change. A rather narrow pH range (5.9–7.7) appeared to allow CH4oxidation. Soils pre-incubated with NH4+had a lower CH4−removal capacity. Moreover, the nitrification inhibitor 2-chloro-6-trichloromethyl pyridine (nitrapyrin) strongly inhibited CH4oxidation. Probably methanotrophs rather than nitrifying microorganisms are mainly responsible for CH4removal in the soil studied. It appears that the causal methanotrophs are remarkably sensitive to soil