Structure And Activity Of Soil Microbial Communities Associated With Methane Emission In Rice Fields

Rice field is an important source of global methane emission. In china, rice yield isthe first and the area for rice cultivation is the second in the world. Methane emission is anet result of production and oxidation by microorganism in paddy soil. It is thus vital tounderstand the microbial mechanism underlying the distinctly different flux of methaneemission in typical soils of rice cultivation across China. In this study, on account of theprocess of methane production and oxidation from typical rice field soil in china, bycultivation-independent techniques such as polymerase chain reaction （PCR）, Real-timequantitative PCR （qPCR）, Denaturing gradient gel electrophoresis （DGGE）, Clone libraryand DNA-based stable isotope probing, et al. we investigated the the abundance andchange of communities structure of methanogens from paddy field soil undergoinglong-term fertilization and elevated CO₂concentration, further studied methane oxidationkinetics and active methane oxidizers were identified in the three geographically distinctsoils typical of rice cultivation in China from Lei-Zhou city （Guangdong province）, Gu-Shicity and Tao-Yuan city （Hu-Nan Province）. The main results were as follows.1. Long-term field fertilization with mineral and organic mixed fertilizers （NPK/OM）increased the abundance of methanogens, especially facilitated the growth ofmicroorganisms affiliated with Methanosarcina, but it appeared to have little effect on thecomposition of methanogens. No significant difference was observed in the structure ofmethanogens communities with inorganic nitrogenous fertilizer treatment only.2. Elevated atmospheric CO₂concentrations increased methanogenic population attillering stage, especially in bulk soil in2009. The abundance of methanogens seemed tobe inhibited at flowering, jointing and grouting stages. Compared with rhizospheric soil,the inhibition of methanogens population was smaller in bulk soil. In addition, the growthof methanogenic population was likely depressed under applying high nitrogenousfertilization than low nitrogenous fertilization.3. At low CH4concentration of⁷00ug·L^-1, CH4oxidation was the fastest inLei-Zhou paddy field （Guangdong province）, while similar methane oxiedation kineticswere observed in rice field of Tao-Yuan and Gu-Shi cities （Hunan province）. At high CH4concentration of⁷000ug·L^-1, the highest methane oxidation rate was observed in rice soil from Gu–Shi city, while there was no significant difference in methane oxidation activitybetween rice paddy soils from Tao-Yuan city and Lei-Zhou city. DNA-based stable isotopeprobing was conducted to link funcational activity and taxonomic identity ofmethane-oxidizing microorganisms in these three typical soils of rice cultivation in China.The results of this study demonstrated distinctly different methaotrophic communitiesinvolved in soil methane oxidation. Type I methanotrophs were exclusively observed inLei-Zhou paddy field, while Tao-Yuan and Gu-Shi paddy soils habored both type I andtype II methanotrophs. Type I methanotrophs were predominant in Gu-Shi paddy field,accounting for77.8%of total methanotrophic communities in soil, while80%of methaneoxidizers were affiliated with type II methanotrophs in Tao-Yuan soils.In summary, the composition of methanogenic communities in rice field soils wasrelatively stable, anthtropogenic disturbance such as long-term field fertilizations andelevated atmospheric CO₂concentrations may stimulate the growth of methanogeniccommunities in paddy soil. The distinctly different kinetics of methane oxidation andactive methanotrophic communities were revealed in geographically distinct rice fileds.