Drought events are predicted to occur more frequently, but comprehensive knowledge of their effects on methane (CH4) oxidation by soil methanotrophs in upland ecosystems remains elusive. Here, we put forward a new conceptual model in which drought influences soil CH4 oxidation through a direct pathway (i.e., positive effects of soil CH4 oxidation via increasing soil aeration) and through an indirect pathway (i.e., negative effects of in planta ethylene (C2H4) production on soil CH4 oxidation). Through measuring soil CH4 efflux along a gradient of drought stress, we found that drought increases soil CH4 oxidation, as the former outweighs the latter on soil CH4 oxidation, based on a mesocosm experiment employing distinct levels of watering and a long-term drought field trial created by rainfall exclusion in a subtropical evergreen forest. Moreover, we used aminoethoxyvinylglycine (AVG), a C2H4 biosynthesis inhibitor, to reduce in planta C2H4 production under drought, and found that reducing in planta C2H4 production increased soil CH4 oxidation under drought. To confirm these findings, we found that inoculation of plant growth-promoting rhizobacteria containing the 1-aminocyclopropane-1-carboxylate deaminase alleviated the negative effects of drought-induced in planta C2H4, thus increasing soil CH4 oxidation rates. All these results provide strong evidence for the hypothesis that in planta C2H4 production inhibits soil CH4 oxidation under drought. To our knowledge, this is the first study to manipulate the negative feedback between C2H4 production and CH4 oxidation under drought stress. Given the current widespread extent of arid and semiarid regions in the world, combined with the projected increased frequency of drought stress in future climate scenarios, we provide a reliable means for increasing soil CH4 oxidation in the context of global warming.
Keywords: Arabidopsis; Drought; Ethylene; Forest; Methane oxidation; Methanotroph.
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