The impacts of post-anthesis warming on grain yield and quality of double-cropping high-quality indica rice in Jiangxi Province, China

Highlights

• 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

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.

Introduction

Compared with the period from 1850 to 1900, the global surface mean temperature for the decade from 2006 to 2015 has increased by 0.87 °C, and this increase is predicted to reach 1.5 °C between 2030 and 2052 (IPCC, 2018). Rice (Oryza sativa L.) is the staple food for nearly half of the world’s population and suffers from climate warming (Xiong et al., 2017). China is the country with the largest rice production and consumption levels in the world. The rice cultivation area of China is approximately 30 million ha, and the grain yield is approximately 210 million tons (FAO, 2018). Three major rice cropping regions in China, namely, single rice cropping systems (Northeast China), middle rice cropping systems (East and central China), and double rice cropping systems (South China), cover more than 90% of China's rice growing area (CNRRI, 1981a). Numerous studies have shown that elevated temperature (e.g., 1.0–2.0 °C) generally decrease japonica grain yield when using open field warming facilities in middle rice cropping systems (Cai et al., 2016, Wang et al., 2016, Wang et al., 2018). However, the influence of elevated temperature on grain yields are equivocal and vary in different rice cropping systems, which might depend on the different air temperature and precipitation patterns across China (Chen et al., 2020). Therefore, we aimed to study the response of indica grain yield to climate warming in double rice cropping systems.

Grain quality mainly refers to the milling, appearance, nutritional, cooking and eating qualities (Fahad et al., 2016). With the improvement of human living standards, consumers have become greatly concerned about the rice cooking and eating quality (Fitzgerald et al., 2009). The formation of grain quality is easily affected by ambient air temperatures, especially in the grain-filling period (Zhong et al., 2005, Xiong et al., 2017). Previous studies showed that high temperature during grain filling induced high occurrences of the chalky rice rate and chalkiness, degraded grain appearance quality, and led to lower milled rice rate in middle rice systems of southern China (Rehmani et al., 2014, Dou et al., 2017, Dou et al., 2018). The rice cooking and eating qualities are usually evaluated by amylose content and rapid viscosity analyser (RVA) parameters. It has been reported that rice with a better taste always has a higher peak viscosity and breakdown and lower amylose content and setback (Jing et al., 2016, Dou et al., 2018). Previous studies have observed that elevated temperature during the grain-filling period decreased the amylose content and setback but increased the peak viscosity, breakdown, and pasting temperature of rice (Liu et al., 2013, Dou et al., 2018). However, the impact of high temperature on the amylose contents also differed by genotype, which was associated with the intrinsic rice amylose content (Zhong et al., 2005). Under high nighttime temperature conditions, the amylose contents of rice cultivars with lower amylose contents could decrease, whereas the trend was opposite for rice cultivars with higher amylose contents (Shi et al., 2013). The protein content of rice is comparatively low, but the proteins in rice constitute a high proportion of human proteins. Previous studies have reported that elevated temperature enhanced both the protein and amino acid contents in milled rice but had little influence on the amino acid proportions of japonica rice cultivars (Dou et al., 2017, Dou et al., 2018). Meanwhile, the rice protein content is also negatively correlated with the rice cooking and eating qualities (Balindong et al., 2018). However, the effects of experimental warming on high-quality indica rice were also not supported by the trial data in double rice cropping systems.

As one of the most important rice cropping systems in China, the planting area and yield of double-cropping rice account for 34.9% and 29.7%, respectively (CNRRI, 1981a). Compared with single rice cropping systems and middle rice cropping systems, double rice cropping systems have continuous and longer growth seasons and different temperatures and light resources between the early and late rice seasons. In addition, indica rice is one of the most important staple food crops in China, especially in double rice cropping systems. To the best of our knowledge, previous studies on the responses of grain yield and quality to elevated temperature were mainly conducted in middle rice cropping systems, but these responses were not reported in double rice cropping systems under field conditions.

Compared to open-top chambers, free air temperature increase (FATI) facilities shed infrared directly on vegetation, which is similar to solar radiation, with little impact on the microclimate conditions in paddy fields; thus, they are used in paddy ecosystem warming experiments to simulate the expected future global warming (Rehmani et al., 2011). Therefore, we established FATI facilities in a double rice cropping system in subtropical China. We hypothesize that the grain yield and quality of high-quality indica rice can be affected by experimental warming in the double rice cropping system, and there are also seasonal differences between early and late rice. For this purpose, a post-anthesis warming (PAW) experiment was carried out with two high-quality indica rice cultivars using FATI facilities in a double rice cropping system. The objectives of this study were to determine the actual responses of grain yield and quality to global warming and to quantify the different responses between early and late rice under PAW.