Microbial mechanism for rice variety control on methane emission from rice field soil

Rice variety is one of the key factors regulating methane (CH4) production and emission from the paddy fields. However, the relationships between rice varieties and populations of microorganisms involved in CH4 dynamics are poorly understood. Here we investigated CH4 dynamics and the composition and abundance of CH4-producing archaea and CH4-oxidizing bacteria in a Chinese rice field soil planted with three types of rice. Hybrid rice produced 50-60% more of shoot biomass than Indica and Japonica cultivars. However, the emission rate of CH4 was similar to Japonica and lower than Indica. Furthermore, the dissolved CH4 concentration in the rhizosphere of hybrid rice was markedly lower than Indica and Japonica cultivars. The rhizosphere soil of hybrid rice showed a similar CH4 production potential but a higher CH4 oxidation potential compared with the conventional varieties. Terminal restriction fragment length polymorphism analysis of the archaeal 16S rRNA genes showed that the hydrogenotrophic methanogens dominated in the rhizosphere whereas acetoclastic methanogens mainly inhabited the bulk soil. The abundance of total archaea as determined by quantitative (real-time) PCR increased in the later stage of rice growth. However, rice variety did not significantly influence the structure and abundance of methanogenic archaea. The analysis of pmoA gene fragments (encoding the alpha-subunit of particulate methane monooxygenase) revealed that rice variety also did not influence the structure of methanotrophic proteobacteria, though variable effects of soil layer and sampling time were observed. However, the total copy number of pmoA genes in the rhizosphere of hybrid rice was approximately one order of magnitude greater than the two conventional cultivars. The results suggest that hybrid rice stimulates the growth of methanotrophs in the rice rhizosphere, and hence enhances CH4 oxidation which attenuates CH4 emissions from the paddy soil. Hybrid rice is becoming more and more popular in Asian countries. The present study demonstrated that planting of hybrid rice will not enhance CH4 emissions albeit a higher grain production than the conventional varieties.