Elevated ozone mitigates warming-induced methane emissions in a rice paddy field

Abstract

Global warming cooccurs with tropospheric ozone (O₃); however, their joined effect on methane (CH₄) emissions in agricultural ecosystems remains largely unknown. Here, a two-year field study was conducted to quantify the effects of elevated O₃ (1.5 ×ambient) and/or warming (ambient+2℃) on CH₄ emissions from paddy fields in a free-air O₃-concentration enrichment and warming system, and to clarify the main influencing factors. Four treatments were applied: (1) ambient O₃ and ambient temperature (CK), (2) elevated O₃ and ambient temperature (E-O₃), (3) ambient O₃ and elevated temperature (W), and (4) elevated O₃ and elevated temperature (E-O₃W). Results showed that elevated O₃ significantly inhibited or tended to inhibit CH₄ emissions from paddy fields at ambient temperature, especially at the jointing and booting stages of rice. Elevated O₃ mitigated the stimulatory effect of warming on CH₄ emissions. The effects of elevated O₃ concentration and warming on CH₄ emission were related to significant changes in soil dissolved organic carbon (DOC) and NH₄⁺ content, but not to the number of rice tillers, soil pH, microbial biomass carbon (MBC), and NO₃^- content. Our study provides evidence that elevated O₃ concentration and warming have an antagonistic effect on CH₄ emissions from paddy fields. To accurately predict global change impacts, the effects of both elevated O₃ and warming should be incorporated within the CH₄ models for paddy fields.