Trade-offs between wheat soil NO emissions and C sequestration under straw return, elevated CO concentration, and elevated temperature.

The feedback between nitrous oxide (NO) emissions, straw management and future climate scenarios is not well understood, especially in wheat ecosystems. In this study, the changes in NO emissions, soil properties, enzymes, and functional genes involved in N cycling were measured with straw return (incorporation and mulching) and straw removal, under elevated [CO] (+200 μmol mol above ambient [CO]), elevated temperature (+2 °C above ambient temperature), and their combination. The net global warming potential (NGWP) and greenhouse gas intensity (GHGI) were evaluated in combination with greenhouse gas emissions, yield, and soil organic carbon (C) sequestration. Compared with the ambient condition, elevated [CO] and elevated temperature suppressed NO emission by 41 %-46 %. Straw return significantly increased NO emission by 31 %-109 % through increasing soil C and N substrates and denitrifying genes abundance, compared with straw removal. In addition, the impact of straw return on NO emission was greater than that of elevated [CO] or temperature. Straw return generally reduced NGWP by 166.2-3353.3 kg CO-eq ha and GHGI by 0.4-1.1 kg CO-eq kg through increasing soil organic C sequestration by 0.1-1.1 t C ha and grain yield by 280.8 kg ha-1595.4 kg ha. Straw return would stimulate NO emissions from this wheat cropping system under future warmer, elevated [CO] climates, but simultaneously increase grain yield and soil organic C sequestration to a greater extent. Overall, straw return is beneficial to climate change mitigation; in particular, straw incorporation would be more effective than straw mulching.