Spatio-kinetic variation of methane oxidizing bacteria in paddy soil at mid-tillering: effect of N-fertilizers

Abstract

Laboratory experiments were conducted to evaluate the variation ofpopulation size of methanotrophs (MOB) and CH₄ oxidation pattern inflooded rice soils sampled at three spatial points (rhizosphere, bulk and baresoils). Rhizosphere soil had higher MOB population size (301.1 ×10⁵ cells g⁻¹ dry soil) than bulk(37.2× 10⁵ cells g⁻¹ dry soil) andbare soil (19.1 × 10⁵ cells g⁻¹dry soil). The population size of MOB followed a decreasing trend with respectto fertilizer (urea ≤ NH₄NO₃ ≤ NH₄Cl≤ control). The result indicated that rhizosphere soil presented thestrongestCH₄ oxidation activities, as shown by the highest values of the twokinetic parameters (K _m(app) andV _max). K _m andV _max increased significantly from bare to bulkto rhizosphere soil in control and fertilized soil and ranged from 6.2 to 133.2μg g⁻¹ dry soil and from 0.03 to 0.41μg h⁻¹ g⁻¹ dry soil,respectively. The differences in K _m andV _max among the three soils (rhizosphere, bulkand bare) in this study could be due to differential species composition ofmethanotrophic community and/or to conditioning of MOB under different soilmicroenvironments. The present study has demonstrated a competitive inhibition effectof NH₄ ⁺-N on CH₄ oxidation.