Relationship between major soil properties and culturable microorganisms affecting CH₄ and N₂O dynamics in rice soils

Abstract

Microorganisms associated with methane (CH₄) and nitrous oxide (N₂O) dynamics were studied in eight rice (Oryza sativa L.) soils by culture-dependent most probable number (MPN) methods. Enumeration of methanogens showed that acetoclastic methanogens (10⁴ to 10⁹ cells g⁻¹) outnumbered lithotrophic methanogens (10³ cells g⁻¹). Serological analysis indicated that type II methanotrophs belonging to Methylosinus and Methylocystis genera are probably the dominant CH₄-oxidizing communities. For chemolithotrophic nitrifiers, nitrite oxidizers outnumbered ammonium oxidizers in most of the studied soils. The populations of both the acetoclastic methanogens (p = 0.05) and methanotrophs (p = 0.06) exponentially increased with the soil pH. Soil denitrifier populations (in a range of 10³ to 10⁶ cells g⁻¹) exponentially decreased as soil C content increased (p = 0.03). Nitrifier and denitrifier populations generally showed a similar trend of variation with soil C/N ratio. The largest nitrifier populations were found in the Texas soil (C/N = 13.9), and largest denitrifier population in the Arkansas soil (C/N = 13.1). The relationships between the studied microbial groups and major soil properties help to understand the dynamics of CH₄ and N₂O production and consumption in soils.

Keywords:

• Methane
• nitrous oxide
• most probable number
• C/N ratio
• rice soils

Acknowledgements

The authors thank Oswald Van Cleemput and Pascal Boeckx from Ghent University, Belgium for suggestions on the draft of the manuscript. This study was supported by the North Atlantic Treaty Organization (NATO) Collaborative Linkage Grant EST-CLG-979858, and the Chinese-Russian Bilateral Collaborative project (NSFC grant No. 40331014 and RFBR grant No. 05-04-39014).