Competitive interactions between methane- and ammonia-oxidizing bacteria modulate carbon and nitrogen cycling in paddy soil

[摘要] Pure culture studies have demonstrated that methanotrophs and ammoniaoxidizers can both carry out the oxidation of methane and ammonia. However,the expected interactions resulting from these similarities are poorlyunderstood, especially in complex, natural environments. Using DNA-basedstable isotope probing and pyrosequencing of 16S rRNA and functional genes,we report on biogeochemical and molecular evidence for growth stimulation ofmethanotrophic communities by ammonium fertilization, and that methanemodulates nitrogen cycling by competitive inhibition of nitrifyingcommunities in a rice paddy soil. Pairwise comparison between microcosmsamended with CH₄, CH₄+Urea, and Urea indicated that ureafertilization stimulated methane oxidation activity 6-fold during a 19-dayincubation period, while ammonia oxidation activity was significantlysuppressed in the presence of CH₄. Pyrosequencing of the total 16S rRNAgenes revealed that urea amendment resulted in rapid growth ofMethylosarcina-like MOB, and nitrifying communities appeared to bepartially inhibited by methane. High-throughput sequencing of the¹³C-labeled DNA further revealed that methane amendment resulted inclear growth of Methylosarcina-related MOB while methane plus urealed to an equal increase in Methylosarcina andMethylobacter-related type Ia MOB, indicating the differentialgrowth requirements of representatives of these genera. An increase in¹³C assimilation by microorganisms related to methanol oxidizers clearlyindicated carbon transfer from methane oxidation to other soil microbes,which was enhanced by urea addition. The active growth of type Iamethanotrops was significantly stimulated by urea amendment, and thepronounced growth of methanol-oxidizing bacteria occurred in CH₄-treatedmicrocosms only upon urea amendment. Methane addition partially inhibited thegrowth of Nitrosospira and Nitrosomonas in urea-amendedmicrocosms, as well as growth of nitrite-oxidizing bacteria. These resultssuggest that type I methanotrophs can outcompete type II methane oxidizers innitrogen-rich environments, rendering the interactions among methane andammonia oxidizers more complicated than previously appreciated.

[学科分类] 地球化学与岩石