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In southern China, climate warming threatens rice production in double rice cropping systems. However, the actual responses of grain yield and quality of high-quality indica rice to climate warming in double rice cropping systems are still unclear. Therefore, a 2-year field post-anthesis warming experiment was conducted by using two high-quality indica rice cultivars (e.g., Qiliangyou2012, early rice; Taiyou398, late rice). The results showed that post-anthesis warming (PAW) increased the rice canopy daily mean temperatures from heading to maturity by an average of 1.9 °C and 2.0 °C over the two years in the early and late rice seasons, respectively. The grain yield, filled grain percentage, and grain weight were not affected by PAW for either early or late rice in the two years. For early rice, PAW decreased the head rice rate and setback, whereas it increased the chalky grain rate, chalkiness, peak viscosity, breakdown, pasting temperature, protein and most amino acid contents. Similarly, the head rice rate, amylose content, and setback of late rice were decreased, whereas the chalky grain rate, chalkiness, peak viscosity, breakdown, protein and most amino acid contents were increased under PAW conditions. These results suggested that PAW worsened the grain milling and appearance qualities and improved the rice eating and nutritional qualities for both early and late rice, while it reduced the cooking quality of early rice. This study provides new insight into improving the grain yield and quality of high-quality indica rice in a double rice cropping system under future climate warming conditions. • Post-anthesis warming (PAW) increased the rice canopy temperature by 1.6–2.4 °C. • PAW did not affect indica rice grain yield in a double rice cropping system. • PAW worsened the milling, appearance, and cooking qualities of indica rice. • PAW could improve the eating and nutritional qualities of indica rice. [ABSTRACT FROM AUTHOR]

The responses of grain yield and greenhouse gas (GHG) emissions to climate warming in rice paddies are serious concerns for both global food security and climate change mitigation. However, the impact of free-air temperature increase (FATI) on grain yield and methane (CH 4) and nitrous oxide (N 2 O) emissions remains unclear for one of the most globally significant rice production practices: the double rice cropping system. Here, we conducted a two-year field experiment to examine the effect of FATI by infrared heaters on grain yield and CH 4 and N 2 O emissions in a double rice field in subtropical China. FATI increased rice canopy temperature by 2.0 °C and soil temperature by 1.2 °C on average but had no effect on either early or late rice yield production. FATI did not affect CH 4 emissions, but significantly increased N 2 O emissions in both the early and late rice seasons. Averaged across two years, N 2 O emissions increased by 0.3 kg ha−1 and 0.7 kg ha−1 in the warmed plots for the early and late rice seasons, respectively. Consequently, FATI enhanced the global warming potential (GWP) and GHG intensity (i.e., yield scaled GWP) in the double rice cropping system. In addition, warming increased the abundance of ammonia-oxidising bacteria, ammonia-oxidising archaea, and a nitrite reductase gene (nirS), but decreased that of a nitrous oxide reductase gene (nosZ). Our results indicate that warming by FATI does not affect grain yield and CH 4 emissions but stimulates N 2 O emissions in the double rice cropping system and therefore promotes a potential positive feedback with future climate warming. • Free-air temperature increase (FATI) with infrared heater was performed in a double rice field. • Moderate warming by FATI had no significant effect on rice yield. • Moderate warming by FATI did not significantly affect CH 4 emissions. • Moderate warming by FATI stimulated N 2 O emissions. [ABSTRACT FROM AUTHOR]

• FATI facility increased canopy temperature by 1.4–2.1 °C in a double rice cropping system. • Experimental warming changed the starch fine structure of indica rice. • Experimental warming deteriorated cooking and eating quality of indica rice starch. To evaluate the actual response of rice starch physicochemical properties to climate warming, a field warming experiment was conducted with four indica rice cultivars using free-air temperature increase (FATI) facility in a double rice cropping system. FATI facility increased rice canopy temperature by 1.4–2.1 °C during the entire growth period. The responses of starch physicochemical properties to experimental warming were basically consistent for both early and late rice. On average, experimental warming increased the starch relative crystallinity, granule average diameter, and amylopectin average chain length by 14.3%, 6.9%, and 2.4%, respectively. These resulted in starch with lower swelling power, water solubility, and pasting viscosity, but higher gelatinization temperatures and gelatinization enthalpy. Our study indicated that experimental warming affected the rice starch physicochemical properties, and would provide some useful information on how to guide the rice starch end use in food and non-food industries under climate warming. [ABSTRACT FROM AUTHOR]

Global warming often affects crop yield and greenhouse gas emissions from cropland. However, the effects of warming on rice yield and methane (CH 4) emissions from rice paddies in the tropical double-rice cropping systems are still unknown. Therefore, we conducted a field experiment to investigate the effect of warming on rice growth and CH 4 emissions in a Chinese tropical double-rice cropping system, using the free air temperature increase facility. The results showed that warming did not affect the rice plant biomass, but significantly reduced the early rice yield by 5.0% and late rice yield by 6.5%. Warming trended to increase CH 4 emissions, especially in the flooded stage of early rice seasons. Warming significantly stimulated the abundance of methanogens and methanotrophs, and CH 4 production and oxidation potential by 93.3%, 84.3%, 29.3% and 66%, respectively. Warming non-significantly increased the soil dissolved organic carbon concentrations, but significantly reduced the soil NH 4 + concentrations. Warming significantly increased yield-scaled CH 4 emissions by 7–41%. Our findings suggest that warming may reduce rice yield but increase CH 4 emissions from the Chinese tropical double-rice cropping systems and underline the need for agricultural practices of higher rice yield and lower CH 4 emissions. • The study was conducted in a Chinese tropical double-rice system. • Warming trended to increase CH 4 emissions, especially in the flooded stage. • Warming increased the abundances of methanogens and methanotrophs. • Warming significantly reduced rice yield and increased yield-scaled CH 4 emissions. [ABSTRACT FROM AUTHOR]