Contribution of Methanotrophic and Nitrifying Bacteria to CH ₄ and NH ₄ ⁺ Oxidation in the Rhizosphere of Rice Plants as Determined by New Methods of Discrimination

Abstract

Methanotrophic and nitrifying bacteria are both able to oxidize CH4 as well as NH4 +. To date it is not possible to estimate the relative contribution of methanotrophs to nitrification and that of nitrifiers to CH4 oxidation and thus to assess their roles in N and C cycling in soils and sediments. This study presents new options for discrimination between the activities of methanotrophs and nitrifiers, based on the competitive inhibitor CH3F and on recovery after inhibition with C2H2. By using rice plant soil as a model system, it was possible to selectively inactivate methanotrophs in soil slurries at a CH4/CH3F/NH4 + molar ratio of 0.1:1:18. This ratio of CH3F to NH4 + did not affect ammonia oxidation, but methane oxidation was inhibited completely. By using the same model system, it could be shown that after 24 h of exposure to C2H2 (1,000 parts per million volume), methanotrophs recovered within 24 h while nitrifiers stayed inactive for at least 3 days. This gave an “assay window” of 48 h when only methanotrophs were active. Applying both assays to model microcosms planted with rice plants demonstrated a major contribution of methanotrophs to nitrification in the rhizosphere, while the contribution of nitrifiers to CH4 oxidation was insignificant.

Methane source strength and energy flow shape methanotrophic communities in oxygen–methane counter‐gradients

“…No nitrite was detected, but nitrate was found in millimolar concentrations at low methane source strength, and in particular upon fertilization (Table S2). In previous experiments with soil from this site, nitrification in rhizospheric soil could be ascribed to MOB (Bodelier and Frenzel, 1999). One of the reverse primers used, A682r, co-amplifies the gene of the bacterial ammonium monooxygenase subunit A (amoA).…”

Aquatic herbivores facilitate the emission of methane from wetlands

“…Potential methane production activity (PMP) was determined as described by Bodelier et al (2006), while potential methane oxidation activity (PMO) was described by Bodelier and Frenzel (1999). For more details see the Appendix.…”

Population dynamics of type I and II methanotrophic bacteria in rice soils

“…Numerous studies have shown, using pure cultures, microcosms and field trials, that nitrogen additions decrease methane oxidation (Bedard and Knowles, 1989;Conrad and Rothfuss, 1991). On the other hand, recent rice microcosm studies (Bodelier and Frenzel, 1999;Bodelier et al, 2000) have clearly shown that N fertilization increases methane oxidation in densely rooted rice soil. N limitation of methane oxidation is compatible with the idea that methanotrophs in rhizosphere soil face intense plant and microbial competition for N. The extent to which methane oxidation takes place in plant roots and rhizospheres compared with at the soil-water interface may influence how methane oxidation and methanotroph populations respond to nitrogen additions, an interaction that few studies have focused on thus far (Conrad and Rothfuss, 1991;Van Der Nat and Middelburg, 1998).…”