Variable effects of 2°C air warming on yield formation under elevated [CO2] in a Chinese double rice cropping system

Elevated atmospheric CO2 concentration ([CO2]) and temperature can strongly affect rice (Oryza sativa L.) production. However, the impact of warming is variable depending on ambient temperature and cropping system. Little is known about the effect of elevated temperature and its interaction with elevated [CO2] in the Chinese double rice cropping system. To study this issue, field experiments were conducted using open-top chambers (OTC) with varying [CO2] (ambient, ambient+60 μmol mol−1) and varying temperature (ambient, ambient+2 °C) for 4 rotations of double rice from 2013 to 2016. Elevated [CO2] significantly increased grain yield in both early rice and late rice. This could be attributed to greater aboveground biomass, higher panicle number (m-2), spikelet number (per panicle) and 1000-grain weight. Elevated temperature decreased yield in early rice (except for 2016) due to decreases in % filled grains and 1000-grain weight. Elevated temperature increased yield in late rice due to increases in aboveground biomass, number of panicles and spikelets, although % filled grains decreased. We found that warming had positive effects on tiller development and dry matter accumulation during the pre-heading period both in early and late rice, which contributed to yield formation. When elevated temperature and [CO2] were combined, yield changed by −1.9–23.7% in early rice compared with ambient condition as warming partly offset the benefits of CO2 enrichment, while yield increased by 14.3–18.8% in late rice due to a synergy between warming and CO2 enrichment. The benefits of CO2 enrichment for fertile spikelets (m-2) and aboveground biomass could reduce or eliminate the negative impacts of warming. However, there were no significant interactions between elevated temperature and [CO2] in most rice seasons. Our findings indicate that warming by 2 °C is not detrimental to yield formation under CO2 enrichment, and suggest that grain yield may not decrease under future climate change in the Chinese double rice cropping system.