Ethylenediurea (EDU) protects inbred but not hybrid cultivars of rice from yield losses due to surface ozone

Both Short-term and Long-term Ozone Pollution Alters the Chemical Composition of rice Grain

The increasing ground-level ozone (O3) is threatening food security, especially in Asian areas, where rice is one of the most important staple crops. O3 impacts on rice could be exacerbated by its spatiotemporal heterogeneity. To improve evaluation accuracy and develop effective adaptations, direct data is urgently needed. Studies on the short-term effects of O3 on rice grain, however, are lacking. Which may lead to an underestimation of the O3 impacts. Through a field experiment, we studied the responses of grain nitrogen, grain carbon, and grain protein in rice cultivars to elevated concentrations of O3 (40 ppb plus that in background air, eO3), especially examining the effects of short-term eO3 during different plant growth stages. We found that long-term eO3 increased grain nitrogen by 29.29% in a sensitive rice cultivar, and short-term eO3 at the tillering and jointing stages increased grain nitrogen by 19.31%, and the grain carbon to nitrogen ratio was decreased by 14.70%, and 21.14% by short-term and long-term eO3. Here we demonstrate that short-term eO3 may significantly affect the chemical composition of rice grains. Previous evaluations of the effects of eO3 may be underestimated. Moreover, changes in the grain nitrogen and grain protein were greater when the short-term eO3 was added to rice plants during the tillering and jointing stage, compared to heading and ripening stage. These results suggest that to improve the tolerance of rice to eO3 to achieve food security, studies on cultivar screening, as well as developing growth-stage-specific adaptations are needed in future.

Can ethylenediurea (EDU) alter the effects of ozone on the source-sink regulation of nitrogen uptake and remobilization during grain filling period in rice?

Increased surface ozone (O3) pollution seriously threatens crop production, and ethylenediurea (EDU) can alleviate crop yield reduction caused by O3. However, the reason for the decrease in grain nitrogen (N) accumulation caused by O3 and whether EDU serves as N fertilizer remain unclear. An experiment was conducted to investigate the impacts of factorial combinations of O3 enrichment (ambient air plus 60 ppb) and EDU (foliage spray with 450 ppm solutions) on N concentration, accumulation and remobilization in hybrid rice seedlings. Compared to ambient condition, elevated O3 significantly inhibited the N accumulation in vegetative organs during anthesis and grain N accumulation during the maturity stage. Elevated O3 significantly decreased the total N accumulation during anthesis and maturity stages, with a greater impact at the latter stage. The decrease in grain N accumulation caused by O3 was attributed to a decrease in N remobilization of vegetative organs during the grain filling period as well as to a decrease in post-anthesis N uptake. However, there was no significant change in the proportion of N remobilization and N uptake in grain N accumulation. The inhibitory effect of O3 on N remobilization in the upper canopy leaves was greater than that in the lower canopy leaves. In addition, elevated O3 increased the N accumulation of panicles at the anthesis stage, mainly by resulting in earlier heading of rice. EDU only increased N accumulation at the maturity stage, which was mainly attributed to an increase in rice biomass by EDU. EDU had no significant effect on N concentration, N remobilization process, and N harvest index. The findings are helpful to better understand the utilization of N fertilizer by rice under O3 pollution, and can also provide a theoretical basis for sustainable nutrient management to alleviate the negative impact of O3 on crop yield and quality.

Wheat yield response to elevated O3 concentrations differs between the world's major producing regions

Ground-level ozone (O3) concentration is rising in Asia, which accommodates the world's top-two wheat producers (China and India). Because wheat is among the species of high O3 sensitivity, yield loss due to rising O3 in Asia is a major threat to global wheat supply. We estimated the relationships between O3 dose on AOT40 (accumulated daytime O3 concentrations above 40 ppb for 90 days) and relative wheat yield for four wheat producing regions: China, India, Europe and North America using results of O3 elevation experiments conducted therein. When compared on the same AOT40, the estimated yield loss was greatest in China followed by India, Europe, and North America in this order. In China, Europe and North America, the yield loss was primarily due to the reduction of single grain weight, whereas in India reduction of the number of grains contributed more to the yield loss than single grain weight. The greater response of the number of grains to O3 in India can be explained by the earlier start of O3 elevation, but the seasonal change in O3 concentrations cannot explain the lower yield loss in North America than China and India. Referring to the past reports of lower yield sensitivity to O3 in older cultivars, we compared the year of release of cultivars between the regions. In North America, they used cultivars released in 1980s or earlier, whereas in China they used cultivars released in 2000s. In Europe and India, most cultivars were released between those in North America and China. The difference in cultivars could therefore be a cause the differential yield response among the regions. We argue that the O3-induced yield loss should be quantified using the dose-response relationships for each region accounting for the effects of seasonal change in O3 concentrations, cultivars and climate on the yield response.

Similar photosynthetic but different yield responses of C3 and C4 crops to elevated O3

The deleterious effects of ozone (O3) pollution on crop physiology, yield, and productivity are widely acknowledged. It has also been assumed that C4 crops with a carbon concentrating mechanism and greater water use efficiency are less sensitive to O3 pollution than C3 crops. This assumption has not been widely tested. Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C3 crops (chickpea, rice, snap bean, soybean, and wheat) and four C4 crops (sorghum, maize, Miscanthus × giganteus, and switchgrass) grown under ambient and elevated O3 concentration ([O3]) in the field at free-air O3 concentration enrichment (O3-FACE) facilities over the past 20 y. When normalized by O3 exposure, C3 and C4 crops showed a similar response of leaf photosynthesis, but the reduction in chlorophyll content, fluorescence, and yield was greater in C3 crops compared with C4 crops. Additionally, inbred and hybrid lines of rice and maize showed different sensitivities to O3 exposure. This study quantitatively demonstrates that C4 crops respond less to elevated [O3] than C3 crops. This understanding could help maintain cropland productivity in an increasingly polluted atmosphere.

Effects of increased ozone on rice panicle morphology

Ground-level ozone threatens rice production, which provides staple food for more than half of the world's population. Improving the adaptability of rice crops to ozone pollution is essential to ending global hunger. Rice panicles not only affect grain yield and grain quality but also the adaptability of plants to environmental changes, but the effects of ozone on rice panicles are not well understood. Through an open top chamber experiment, we investigated the effects of long-term and short-term ozone on the traits of rice panicles, finding that both long-term and short-term ozone significantly reduced the number of panicle branches and spikelets in rice, and especially the fertility of spikelets in hybrid cultivar. The reduction in spikelet quantity and fertility because of ozone exposure is caused by changes in secondary branches and attached spikelet. These results suggest the potential for effective adaptation to ozone by altering breeding targets and developing growth stage-specific agricultural techniques.

Impacts of Climate Change on Rice Grain: A Literature Review on What Is Happening, and How Should We Proceed?

More than half of the people on Earth get their calories, proteins, and minerals from rice grains. Staple increases in the quantity and quality of rice grains are key to ending hunger and malnutrition. Rice production, however, is vulnerable to climate change, and the climate on Earth is becoming more fluctuating with the atmospheric change induced by human activities. As a result, the impacts of climate change on rice grain (ICCRG) have sparked widespread concern. In order to reveal the development and the trend in the study on the ICCRG, a bibliometric analysis was conducted. The results showed that both the model simulations and the field experiment-based observations, as reflected by APSIM (the Agricultural Production Systems sIMulator) and free-air carbon dioxide (CO₂) enrichment, are of concern to researchers worldwide, especially in China, India, the United States, and Japan. Different types of warming include short-term, nighttime, soil and water, and canopy, and their interactions with other climate factors, such as CO₂, or agronomic factors, such as nitrogen level, are also of concern to researchers. Spatiotemporal variations in changing weather and regional adaptations from developed and developing countries are challenging the evaluation of ICCRG from an economic perspective. In order to improve the efficacy of breeding adaptable cultivars and developing agronomic management, interdisciplinary studies integrating molecular biology, plant physiology, agronomy, food chemistry, ecology, and socioeconomics are needed.

Food Security in China: A Brief View of Rice Production in Recent 20 Years

Rice production affects the food security and socioeconomic status of over half the world’s population. Rice-producing countries, however, are facing population growth, reduction in rice planting area, and global change. Understanding the trends of rice production and major determinants is key to regulating rice production. We thus analyzed the trends of rice production and related determinants in China from 2001 to 2021, revealing that the annual rice production (TRP) has risen steadily (r = 0.929, p < 0.0001) in recent 20 years. TRP in 2021 was 19.9% higher than that in 2001, which was primarily achieved by the increment of middle rice production (MRP). MRP increased by 46.2% from 2000 to 2018, and grain yield per unit area (GPA) was the largest in middle rice. The enhancement of GPAs is significantly correlated with the consumption of agricultural resources and the number of released rice cultivars, but variations exist. TRP and GPA vary in different provinces; Hunan (25 ± 2 megatons) and Xinjiang (8364 ± 806 kg/hectare) show the largest values, respectively. TRP could be further increased by 13.8% by improving MRP. The results suggest that rice production in China has a large potential to be further improved through regulations.

Ethylenediurea reduces grain chalkiness in hybrid rice cultivars under ambient levels of surface ozone in China

High concentration of tropospheric ozone (O3) causes crop yield losses, which could be reduced by foliar application of ethylenediurea (EDU). Rice grain appearance is a major quality trait that determines the milling quality, white rice productivity and the market value. Grain chalkiness is one of the common defects that deteriorate the grain appearance in rice due to its negative effects on palatability and milling yield. Whether EDU could reduce grain chalkiness in rice which was usually increased by high concentration of O3 is not clarified. We report the grain chalkiness in 19 rice cultivars (CVs) of three types: indica (6 CVs), japonica (5 CVs) and hybrids (8 CVs), observed in an EDU application experiment in the field in China. The ambient O3 level as expressed by accumulated hourly O3 concentration over the threshold of 40 ppb (AOT40) for 80 days until maturity reached 12.8 ppm h at a near-by monitoring station. Fraction of the chalky grains (FCG) in the hybrid cultivars was 8% lower in EDU than that in the control treatments, whereas no significant effect of EDU on FCG was found in japonica or indica cultivars. The reduction of FCG due to EDU treatment in hybrid cultivars was attributed to the significant reduction of milky white grains followed by that of white belly grains. Thus, the application of EDU could ameliorate the decline of grain appearance quality in hybrid rice by decreasing the FCG and enhancing the fraction of perfect grains (FPG). Moreover, there were significant interactions between the EDU application and rice cultivars, indicating varietal difference in the protection of grain appearance quality by EDU. These results suggest the need for further studies on the mechanisms of the effects of EDU on grain chalkiness.

Effects of elevated ozone on bacterial communities inhabiting the phyllo- and endo-spheres of rice plants

To explore the effects of elevated ozone (O₃) on microbial communities inhabiting phyllo- and endo-spheres of Japonica rice leaves, cultivars Nangeng 5055 (NG5055) and Wuyujing 27 (WYJ27) were grown in either charcoal-filtered air (CF) or elevated O₃ (ambient O₃ + 40 ppb, E-O₃) in field open-top chambers (OTCs) during a growing season. E-O₃ increased the values of the Shannon (43-80%) and Simpson (34-51%) indexes of the phyllo-and endo-spheric bacterial communities in NG5055. E-O₃ also increased the values of the phyllosphere Simpson index by 58% and the endosphere Shannon index by 54% in WYJ27. Both diversity indexes positively correlated with the contents of nitrogen, phosphorus, magnesium, and soluble sugar, and negatively correlated with the contents of starch and condensed tannins. The leaf-associated bacterial community composition significantly changed in both rice cultivars under E-O₃. Moreover, the leaf-associated bacterial communities in NG5055 were more sensitive to E-O₃ than those in WYJ27. The chemical properties explained 70% and 98% of variations in the phyllosphere and endosphere bacterial communities, respectively, suggesting a predominant role of chemical status for the endospheric bacterial community. Most variation (57.3%) in the endosphere bacterial community assembly was explained by phosphorus. Gammaproteobacteria and Pantoea were found to be the most abundant class (63-76%) and genus (38-48%) in the phyllosphere and endosphere, respectively. E-O₃ significantly increased the relative abundance of Bacteroidetes in the phyllosphere bacterial community and decreased the relative abundance of Gammaproteobacteria in the endophytic community. In conclusion, elevated O₃ increased the diversity of bacterial communities of leaf phyllosphere and endosphere, and leaf chemical properties had a more pronounced effect on the endosphere bacterial community.

Ozone pollution threatens the production of major staple crops in East Asia

East Asia is a hotspot of surface ozone (O₃) pollution, which hinders crop growth and reduces yields. Here, we assess the relative yield loss in rice, wheat and maize due to O₃ by combining O₃ elevation experiments across Asia and air monitoring at about 3,000 locations in China, Japan and Korea. China shows the highest relative yield loss at 33%, 23% and 9% for wheat, rice and maize, respectively. The relative yield loss is much greater in hybrid than inbred rice, being close to that for wheat. Total O₃-induced annual loss of crop production is estimated at US$63 billion. The large impact of O₃ on crop production urges us to take mitigation action for O₃ emission control and adaptive agronomic measures against the rising surface O₃ levels across East Asia.