Manipulation of soil methane oxidation under drought stress

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.