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

Y. Zheng, R. Huang, B. Z. Wang, P. L. E. Bodelier, Z. J. Jia
2014 Biogeosciences  
<p><strong>Abstract.</strong> Pure culture studies have demonstrated that methanotrophs and ammonia oxidizers can both carry out the oxidation of methane and ammonia. However, the expected interactions resulting from these similarities are poorly understood, especially in complex, natural environments. Using DNA-based stable isotope probing and pyrosequencing of 16S rRNA and functional genes, we report on biogeochemical and molecular evidence for growth stimulation of methanotrophic communities
more » ... trophic communities by ammonium fertilization, and that methane modulates nitrogen cycling by competitive inhibition of nitrifying communities in a rice paddy soil. Pairwise comparison between microcosms amended with CH<sub>4</sub>, CH<sub>4</sub>+Urea, and Urea indicated that urea fertilization stimulated methane oxidation activity 6-fold during a 19-day incubation period, while ammonia oxidation activity was significantly suppressed in the presence of CH<sub>4</sub>. Pyrosequencing of the total 16S rRNA genes revealed that urea amendment resulted in rapid growth of <i>Methylosarcina</i>-like MOB, and nitrifying communities appeared to be partially inhibited by methane. High-throughput sequencing of the <sup>13</sup>C-labeled DNA further revealed that methane amendment resulted in clear growth of <i>Methylosarcina</i>-related MOB while methane plus urea led to an equal increase in <i>Methylosarcina</i> and <i>Methylobacter</i>-related type Ia MOB, indicating the differential growth requirements of representatives of these genera. An increase in <sup>13</sup>C assimilation by microorganisms related to methanol oxidizers clearly indicated carbon transfer from methane oxidation to other soil microbes, which was enhanced by urea addition. The active growth of type Ia methanotrops was significantly stimulated by urea amendment, and the pronounced growth of methanol-oxidizing bacteria occurred in CH<sub>4</sub>-treated microcosms only upon urea amendment. Methane addition partially inhibited the growth of <i>Nitrosospira</i> and <i>Nitrosomonas</i> in urea-amended microcosms, as well as growth of nitrite-oxidizing bacteria. These results suggest that type I methanotrophs can outcompete type II methane oxidizers in nitrogen-rich environments, rendering the interactions among methane and ammonia oxidizers more complicated than previously appreciated.</p>
doi:10.5194/bg-11-3353-2014 fatcat:plv6lvpiyjfmlmg3xtgnzsw5eu