Comparison of methanotrophic bacteria, methane oxidation activity, and methane emission in rice fields fertilized with anaerobically digested slurry between a fodder rice and a normal rice variety

Abstract

Methane oxidation activity (MOA), methanotrophic bacteria (MOB), and CH₄ emission in a paddy field fertilized with anaerobically digested slurry were compared between two varieties: a fodder rice variety Leaf star (LS) and a normal rice variety Kinuhikari (KN). Average MOA and MOB per unit dry root were significantly higher in KN (7.1 μmol g⁻¹ CH₄ g⁻¹ dry root h⁻¹ and 3.7 × 10⁷ MPN g⁻¹ dry root, respectively) than in LS (4.3 μmol g⁻¹ CH₄ g⁻¹ dry root h⁻¹, 2.1 × 10⁷ MPN g⁻¹ dry root), although MOA in the rice root per whole plant was not significantly different since root biomass of LS (1.5 g dry root plant⁻¹) was significantly higher than that of KN (1.2 g dry root plant⁻¹). MOA in the soil ranged from 0.031 to 0.087 μmol g⁻¹ CH₄ g⁻¹ dry soil h⁻¹, but there were no significant differences in both depths (0–5 and 5–15 cm) between the two rice varieties. MOA in the rhizosphere soil was significantly different between the rice varieties at flowering, but not at tillering. Methane emission in the field was lower and MOA and MOB in the rice root were higher in LS than in KN at tillering, but the reverse results were found at flowering and maturity stages. Total CH₄ emission during a growing period was not significantly different between LS (27.4 ± 16.9 g CH₄ m⁻²) and KN (24.0 ± 19.5 g CH₄ m⁻²). There was a significant negative relationship between CH₄ emission and rice root MOB (P < 0.01) or MOA (P < 0.05) and significant positive relationship was observed between root MOA and MOB (P < 0.01). This study revealed that choice of rice variety might be an important environmental issue in paddy cultivation since it can influence MOA and MOB in rice root and rhizosphere soil which relate with CH₄ emission.