The impact of elevated CO2 and temperature on grain quality of rice grown under open-air field conditions

Selenium nanoparticles induce coumarin metabolism and essential oil production in Trachyspermum ammi under future climate CO2 conditions

Research on nanoparticles (NPs) and future elevated CO2 (eCO2) is extensive, but the effects of SeNPs on plant growth and secondary metabolism under eCO2 remain uncertain. In this study, we explored the impact of SeNPs and/or eCO2 on the growth, physiology, chemical composition (primary metabolites, coumarins, and essential oils), and antioxidant capacity of Trachyspermum (T.) ammi. The treatment with SeNPs notably improved the biomass and photosynthesis of T. ammi plants, particularly under eCO2 conditions. Plant fresh and dry weights were improved by about 19, 33 and 36% in groups treated by SeNPs, eCO2, and SeNPs + eCO2, respectively. SeNPs + eCO2 induced photosynthesis, consequently enhancing sugar and amino acid levels. Similar to the increase in total sugars, amino acids showed variable enhancements ranging from 6 to 42% upon treatment with SeNPs + eCO2. At the level of the secondary metabolites, SeNPs + eCO2 substantially augmented coumarin biosynthesis and essential oil accumulation. Consistently, there were increases in coumarins and essential oil precursors (shikimic and cinnamic acids) and their biosynthetic enzymes. The enhanced accumulation of coumarins and essential oils resulted in increased overall antioxidant activity, as evidenced by improvements in FRAP, ORAC, TBARS, conjugated dienes, and inhibition % of hemolysis. Conclusively, the application of SeNPs demonstrates significant enhancements in plant growth and metabolism under future CO2 conditions, notably concerning coumarin metabolism and essential oil production of T. ammi.

Experimental Warming Increased Cooked Rice Stickiness and Rice Thermal Stability in Three Major Chinese Rice Cropping Systems

Climate warming is a critical environmental issue affecting rice production. However, its effects on cooked rice texture and rice thermal properties remain unstudied in China. To address this gap, we conducted a two-year multi-site field warming experiment using free-air temperature increase facilities across three major Chinese rice cropping systems. Interestingly, warming had a minimal impact on the hardness of cooked rice, while it significantly increased stickiness by an average of 16.3% under warming conditions. Moreover, compared to control treatments, rice flour exhibited a significant increase in gelatinization enthalpy, onset, peak, and conclusion temperatures under warming conditions, with average increments of 8.7%, 1.00 °C, 1.05 °C, and 1.17 °C, respectively. In addition, warming significantly declined the amylose content, remarkedly elevated the protein content and relative crystallinity, and altered the weight distribution of the debranched starch. Correlation analysis revealed significant relationships between cooked rice stickiness, rice flour thermal properties, amylose content, protein content, and partial starch structures. Therefore, warming-induced alterations in rice composition and starch structure collectively enhanced cooked rice stickiness and rice thermal stability.

Effects of nitrogen application on physicochemical properties of rice starch under elevated temperature

Nitrogen fertilization can mitigate the negative effects of high temperatures on rice. In this study, we simulated dynamic field temperature increases using a free-air temperature enhancement system. Changes in the physicochemical properties of starch were investigated under increasing nitrogen fertilization during the grain-filling stage. We observed that the application of nitrogen at elevated temperatures (ETN) did not change the chain length distribution compared with elevated temperatures (ET) alone; however, it did significantly increase the heights of the first and second amylose peaks. Specifically, ETN significantly decreased the height of fifth amylopectin and relative crystallinity, and the changes it introduced in the physicochemical properties of starch were greater than those of ET. Overall, these changes in starch properties may be associated with the ability of nitrogen to facilitate the maintenance of rice quality at high temperatures.

Revisiting Changes in Growth, Physiology and Stress Responses of Plants under the Effect of Enhanced CO2 and Temperature

Climate change has universally affected the whole ecosystem in a unified manner and is known to have improbable effects on agricultural productivity and food security. Carbon dioxide (CO2) and temperature are the major environmental factors that have been shown to increase sharply during the last century and are directly responsible for affecting plant growth and development. A number of previous investigations have deliberated the positive effects of elevated CO2 on plant growth and development of various C3 crops, while detrimental effects of enhanced temperature on different crop plants like rice, wheat, maize and legumes are generally observed. A combined effect of elevated CO2 and temperature has yet to be studied in great detail; therefore, this review attempts to delineate the interactive effects of enhanced CO2 and temperature on plant growth, development, physiological and molecular responses. Elevated CO2 maintains leaf photosynthesis rate, respiration, transpiration and stomatal conductance in the presence of elevated temperature and sustains plant growth and productivity in the presence of both these environmental factors. Concomitantly, their interaction also affects the nutritional quality of seeds and leads to alterations in the composition of secondary metabolites. Elevated CO2 and temperature modulate phytohormone concentration in plants, and due to this fact, both environmental factors have substantial effects on abiotic and biotic stresses. Elevated CO2 and temperature have been shown to have mitigating effects on plants in the presence of other abiotic stress agents like drought and salinity, while no such pattern has been observed in the presence of biotic stress agents. This review focuses on the interactive effects of enhanced CO2 and temperature on different plants and is the first of its kind to deliver their combined responses in such detail.

Effects of elevated atmospheric [CO2] on grain starch characteristics in different specialized wheat

The increasing atmospheric [CO2] poses great challenges to wheat production. Currently, the response of starch characteristics in different specialized wheat cultivars to elevated [CO2], as well as the underlying physiological and molecular mechanisms remains unclear. Therefore, an experiment was conducted with open-top chambers to study the effects of ambient [CO2] [a(CO2)] and elevated [CO2] [e(CO2)] on photosynthetic performance, yield and starch characteristics of bread wheat (Zhengmai 369, ZM369) and biscuit wheat (Yangmai 15, YM15) from 2020 to 2022. The results demonstrated a significant improvement in photosynthetic performance, yield, amylose and amylopectin content, volume ratio of large granules under e[CO2]. Moreover, e[CO2] upregulated the gene expression and enzyme activities of GBSS (Granule-bound starch synthase) and SSS (Soluble starch synthase), increased starch pasting viscosity, gelatinization enthalpy and crystallinity. Compared to YM15, ZM369 exhibited a higher upregulation of GBSSI, greater increase in amylose content and volume ratio of large granules, as well as higher gelatinization enthalpy and crystallinity. However, ZM369 showed a lower increase in amylopectin content and a lower upregulation of SSSI and SSSII. Correlation analysis revealed amylose and amylopectin content had a positive correlation with GBSS and SSS, respectively, a significant positively correlation among the amylose and amylopectin content, starch granule volume, and pasting properties. In conclusion, these changes may enhance the utilization value of biscuit wheat but exhibit an opposite effect on bread wheat. The results provide a basis for selecting suitable wheat cultivars and ensuring food security under future climate change conditions.

Rapeseed plant: biostimulation effects of plant growth-promoting Actinobacteria on metabolites and antioxidant defense system under elevated CO2 conditions

BACKGROUND

The present study set out to evaluate the potential of plant growth-promoting Actinobacteria (PGPB) in improving some physiological and molecular parameters of rapeseed (Brassica napus L.) plants under ambient and elevated CO2 conditions by assessing some nitrogen- and sulfur-containing metabolites, antioxidant defense system and antimicrobial activity. With this aim, a pot experiment was conducted where the rapeseed plants were treated with Actinobacterium sp. strain NCO2 (OQ451136) and were grown under two levels of air CO2 concentrations: ambient CO2 (aCO2 , 410 μmol CO2  mol-1 ); and elevated CO2 (eCO2 , 710 μmol CO2  mol-1 ).

RESULTS

There was an increase in the photosynthetic pigments (+35-80%) and photosynthesis rate (+20-34%) in PGPB-treated plants under eCO2 compared to control plants, resulting in further growth and biomass production (+53-294%). These results were associated with an enhancement in the content of total antioxidant capacity (+15-128%), polyphenols (+21-126%) and α-tocopherols (+20-138%) under both eCO2 and PGPB application (in combination or individual application), while only the combined treatment (eCO2  + PGPB) led to a significantly higher accumulation of antioxidant enzymes (+88-197%), β-tocopherols (+177%) and flavonoids (+155%). Moreover, nitrogen- and sulfur-containing metabolites (glucosinolates and amino acids) were improved by PGPB treatment and/or CO2 levels, in which PGPB increased the amino acid-derived glucosinolate induction by eCO2 with low levels of effective sulforaphane.

CONCLUSIONS

Therefore, the interaction effects of beneficial Actinobacteria and eCO2 are expected to boost the level of antioxidant molecules and to have a helpful role in improving plant biomass and adaptability to complicated climate changes in the future. © 2023 Society of Chemical Industry.

Physiological and biochemical responses of wheat to synergistic effects of selenium nanoparticles and elevated CO2 conditions

Elevating CO₂ (eCO₂) levels will change behavior and the effect of soil fertilizers and nutrients. Selenium NPs (SeNPs) have arisen as an alternative to conventional Se fertilizers to enrich crops. However, it remains unclear whether eCO₂ will change the biological effects of soil SeNPs on plant growth and metabolism. The current study aimed to shed new light on the interactive impacts of eCO₂ and SeNPs on wheat plants. Accordingly, the attempts were to reveal whether the application of SeNPs can modulate the eCO₂ effects on wheat (Triticum aestivum L.) physiological and biochemical traits. With this goal, a pot experiment was carried out where the seeds were primed with SeNPs and plants were grown under two levels of CO₂ concentrations (ambient CO₂ (aCO₂, 410 μmol CO₂ mol^-1; and eCO₂ (710 μmol CO₂ mol^-1)) during six weeks after sowing. Although SeNPs+eCO₂ treatment resulted in the highest accumulation of photosynthetic pigment content in leaves (+49-118% higher than control), strong evidence of the positive impacts on Rubisco activity (~+23%), and stomatal conductance (~+37%) was observed only under eCO₂, which resulted in an improvement in photosynthesis capacity (+42%). When photosynthesis parameters were stimulated with eCO₂, a significant improvement in dry matter production was detected, in particular under SeNPs+eCO₂ which was 1.8 times higher than control under aCO₂. The highest content of antioxidant enzymes, molecules, and metabolites was also recorded in SeNPs+eCO₂, which might be associated with the nearly 50% increase in sodium content in shoots at the same treatment. Taken together, this is the first research documenting the effective synergistic impacts of eCO₂ and SeNPs on the mentioned metabolites, antioxidants, and some photosynthetic parameters, an advantageous consequence that was not recorded in the individual application of these treatments, at least not as broadly as with the combined treatment.

Grain yield and quality performances of different late-season rice cultivars in response to experimental warming in subtropical China

Introduction

Climate warming has pronounced effects on rice production in China. However, late-seasons rice cultivars are diverse in double rice cropping systems, and the actual responses in grain yield and quality of different late-season rice cultivars to climate warming are still unclear.

Methods

A two-year field warming experiment was conducted by using free-air temperature increase facilities with three widely-planted late-season rice cultivars, including Taiyou398 (TY, short growth duration indica hybrid rice), Jiuxiangnian (JXN, long growth duration indica inbred rice), and Yongyou1538 (YY, long growth duration indica-japonica hybrid rice) in a double rice cropping system in subtropical China.

Results

Warming (1.9-2.0°C) had no significant effects on the grain yields of TY and JXN, but significantly decreased that of YY by 4.8% relative to ambient treatment due to a reduction of spikelet number. Compared to ambient treatment, the head rice yields of TY and YY did not change while that of JXN increased by 6.3% under warming conditions. Warming significantly increased the head rice rates of JXN and YY by 6.6% and 7.8%, and the chalky grain rates of TY, JXN, and YY by 79.1%, 21.6%, and 7.6%, respectively. Under warming conditions, the amylose content of JXN and YY decreased significantly by 7.5% and 8.8%, and the setback of three cultivars decreased significantly by an average of 41.5%.

Conclusion

Warming could improve the milling and eating qualities of long growth duration late-season rice (JXN and YY) and increase or maintain their head rice yield, even though decreased the grain yield of indica-japonica hybrid rice (YY). These results will provide a better understanding for the selection of suitable late-season rice cultivars under future climate warming conditions.

Effect of climate warming on the grain quality of early rice in a double-cropped rice field: A 3-year measurement

Introduction

The threat of climate warming to global rice production has been widely addressed, but little is known about its influence on the quality of rice grains.

Methods

A free-air temperature increase (FATI) facility with two widely-planted high-quality cultivars was used to explore the impact of warming on the grain quality of early rice in subtropical China over 3 consecutive years.

Results

Compared with the control, FATI increased diurnal canopy temperature by 1.5°, and thus, rice growth duration was shortened by 4.0 d under warming. We found that warming significantly reduced both the milled rice and head rice rates relative to the control, thereby leading to a decrease in the milled rice and head rice yield by 3.9 and 8.3%, respectively. The chalky grain rate and chalkiness were increased by 19.1 and 22.2% under warming compared with the control, respectively. The content of protein, essential amino acids, and non-essential amino acids were increased by 4.1, 5.4, and 4.9% under warming, respectively. Warming reduced the amylose content and setback by 2.0 and 47.5% but increasing peak viscosity, trough viscosity, breakdown, and final viscosity by 9.5, 13.6, 5.7, and 6.0%, respectively.

Conclusion

Our results suggest that the deteriorated milling and appearance quality induced by warming may be an upcoming challenge for high-quality early rice production in the future.

Response of Source-Sink Characteristics and Rice Quality to High Natural Field Temperature During Reproductive Stage in Irrigated Rice System

Global warming greatly affects the development of rice at different growth stages, thereby deteriorating rice quality. However, the effect of high natural field temperature during reproductive stages on rice quality is unclear. Thus, grain filling dynamics, source-sink characteristics and quality-related traits were compared between two contrasting natural field temperature conditions namely normal (low temperature) (LRT) and hot (high temperature) growth season (HRT) during reproductive stage. Compared with LRT, HRT significantly increased chalky grain rate (about 1.6-3.1%), chalkiness level (about 4.7-22.4%), protein content (about 0.93-1.07%), pasting temperature, setback, and consistence, and decreased total starch content (about 4.6-6.2%). Moreover, HRT significantly reduced the leaf area index (LAI, about 0.54-1.11 m2 m-2), specific leaf weight (SLW, about 1.27-1.44 mg cm-2) and source-sink ratio (leaf-sink ratio and/or stem-sink ratio), shortened the active grain filling period by 3.1-3.2 days, and reduced the rations of dry matter translocation to grain (RDMs). In conclusion, we suggested that significant reduction in assimilate translocation after flowering, resulting in the reduced active grain-filling duration and the poor rice quality (high chalkiness and the poor eating and cooking quality), modulated by source-sink characteristics in response to high natural field temperature during reproductive stage. These results enriched the study of high temperature-stressed rice and served as an important reference for selecting high-quality, heat-tolerant varieties and protecting rice quality under high-temperature conditions.

Molecular and Metabolic Changes under Environmental Stresses: The Biosynthesis of Quality Components in Preharvest Tea Shoots

Severe environments impose various abiotic stresses on tea plants. Although much is known about the physiological and biochemical responses of tea (Camellia sinensis L.) shoots under environmental stresses, little is known about how these stresses impact the biosynthesis of quality components. This review summarizes and analyzes the changes in molecular and quality components in tea shoots subjected to major environmental stresses during the past 20 years, including light (shade, blue light, green light, and UV-B), drought, high/low temperature, CO2, and salinity. These studies reveal that carbon and nitrogen metabolism is critical to the downstream biosynthesis of quality components. Based on the molecular responses of tea plants to stresses, a series of artificial methods have been suggested to treat the pre-harvest tea plants that are exposed to inhospitable environments to improve the quality components in shoots. Furthermore, many pleiotropic genes that are up- or down-regulated under both single and concurrent stresses were analyzed as the most effective genes for regulating multi-resistance and quality components. These findings deepen our understanding of how environmental stresses affect the quality components of tea, providing novel insights into strategies for balancing plant resistance, growth, and quality components in field-based cultivation and for breeding plants using pleiotropic genes.

Impact of Elevated CO2 and Reducing the Source-Sink Ratio by Partial Defoliation on Rice Grain Quality - A 3-Year Free-Air CO2 Enrichment Study

Evaluating the impact of increasing CO₂ on rice quality is becoming a global concern. However, whether adjusting the source-sink ratio will affect the response of rice grain quality to elevated CO₂ concentrations remains unknown. In 2016-2018, we conducted a free-air CO₂ enrichment experiment using a popular japonica cultivar grown at ambient and elevated CO₂ levels (eCO₂, increased by 200 ppm), reducing the source-sink ratio via cutting leaves (LC) at the heading stage, to investigate the effects of eCO₂ and LC and their interactions on rice processing, appearance, nutrition, and eating quality. Averaged across 3 years, eCO₂ significantly decreased brown rice percentage (-0.5%), milled rice percentage (-2.1%), and head rice percentage (-4.2%) but increased chalky grain percentage (+ 22.3%) and chalkiness degree (+ 26.3%). Markedly, eCO₂ increased peak viscosity (+ 2.9%) and minimum viscosity (+ 3.8%) but decreased setback (-96.1%) of powder rice and increased the appearance (+ 4.5%), stickiness (+ 3.5%) and balance degree (+ 4.8%) of cooked rice, while decreasing the hardness (-6.7%), resulting in better palatability (+ 4.0%). Further, eCO₂ significantly decreased the concentrations of protein, Ca, S, and Cu by 5.3, 4.7, 2.2, and 9.6%, respectively, but increased K concentration by 3.9%. Responses of nutritional quality in different grain positions (brown and milled rice) to eCO₂ showed the same trend. Compared with control treatment, LC significantly increased chalky grain percentage, chalkiness degree, protein concentration, mineral element levels (except for B and Mn), and phytic acid concentration. Our results indicate that eCO₂ reduced rice processing suitability, appearance, and nutritional quality but improved the eating quality. Rice quality varied significantly among years; however, few CO₂ by year, CO₂ by LC, or CO₂ by grain position interactions were detected, indicating that the effects of eCO₂ on rice quality varied little with the growing seasons, the decrease in the source-sink ratios or the different grain positions.

Effect of Elevated CO2 on Biomolecules' Accumulation in Caraway (Carum carvi L.) Plants at Different Developmental Stages

Caraway plants have been known as a rich source of phytochemicals, such as flavonoids, monoterpenoid glucosides and alkaloids. In this regard, the application of elevated CO₂ (eCO₂) as a bio-enhancer for increasing plant growth and phytochemical content has been the focus of many studies; however, the interaction between eCO₂ and plants at different developmental stages has not been extensively explored. Thus, the present study aimed at investigating the changes in growth, photosynthesis and phytochemicals of caraway plants at two developmental stages (sprouts and mature tissues) under control and increased CO₂ conditions (ambient CO₂ (a CO₂, 400 ± 27 μmol CO₂ mol^-1 air) and eCO₂, 620 ± 42 μmol CO₂ mol^-1 air ppm). Moreover, we evaluated the impact of eCO₂-induced changes in plant metabolites on the antioxidant and antibacterial activities of caraway sprouts and mature plants. CO₂ enrichment increased photosynthesis and biomass accumulation of both caraway stages. Regarding their phytochemical contents, caraway plants interacted differently with eCO₂, depending on their developmental stages. High levels of CO₂ enhanced the production of total nutrients, i.e., carbohydrates, proteins, fats and crude fibers, as well as organic and amino acids, in an equal pattern in both caraway sprouts and mature plants. Interestingly, the eCO₂-induced effect on minerals, vitamins and phenolics was more pronounced in caraway sprouts than the mature tissues. Furthermore, the antioxidant and antibacterial activities of caraway plants were enhanced under eCO₂ treatment, particularly at the mature stage. Overall, eCO₂ provoked changes in the phytochemical contents of caraway plants, particularly at the sprouting stage and, hence, improved their nutritive and health-promoting properties.

A meta-analysis of the combined effects of elevated carbon dioxide and chronic warming on plant %N, protein content and N-uptake rate

Elevated CO₂ (eCO₂) and high temperatures are known to affect plant nitrogen (N) metabolism. Though the combined effects of eCO₂ and chronic warming on plant N relations have been studied in some detail, a comprehensive statistical review on this topic is lacking. This meta-analysis examined the effects of eCO₂ plus warming on shoot and root %N, tissue protein concentration (root, shoot and grain) and N-uptake rate. In the analyses, the eCO₂ treatment was categorized into two classes (<300 or ≥300 ppm above ambient or control), the temperature treatment was categorized into three classes (<1.5, 1.5-5 and >5 °C above ambient or control), plant species were categorized based on growth form and functional group and CO₂ treatment technique was also investigated. Elevated CO₂ alone or in combination with warming reduced shoot %N (more so at ≥300 vs. <300 ppm above ambient CO₂), while root %N was significantly reduced only by eCO₂; warming alone often increased shoot %N, but mostly did not affect root %N. Decreased shoot %N with eCO₂ alone or eCO₂ plus warming was greater for woody and non-woody dicots than for grasses, and for legumes than non-legumes. Though root N-uptake rate was unaffected by eCO₂, eCO₂ plus warming decreased N-uptake rate, while warming alone increased it. Similar to %N, protein concentration decreased with eCO₂ in shoots and grain (but not roots), increased with warming in grain and decreased with eCO₂ and warming in grain. In summary, any benefits of warming to plant N status and root N-uptake rate will generally be offset by negative effects of eCO₂. Hence, concomitant increases in CO₂ and temperature are likely to negate or decrease the nutritional quality of plant tissue consumed as food by decreasing shoot %N and shoot and/or grain protein concentration, caused, at least in part, by decreased root N-uptake rate.

Responses of rice qualitative characteristics to elevated carbon dioxide and higher temperature: implications for global nutrition

BACKGROUND

Protein and some minerals of rice seed are negatively affected by projected carbon dioxide (CO₂ ) levels. However, an in-depth assessment of rice quality that encompasses both CO₂ and temperature for a wide range of nutritional parameters is not available. Using a free-air CO₂ enrichment facility with temperature control, we conducted a field experiment with two levels of CO₂ (ambient; ambient + 200 ppm) and two levels of temperature (ambient; ambient + 1.5 °C). An in-depth examination of qualitative factors indicated a variable nutritional response.

RESULTS

For total protein, albumin, glutelin, and prolamin, elevated CO₂ reduced seed concentrations irrespective of temperature. Similarly, several amino acids declined further as a function of higher temperature and elevated CO₂ relative to elevated CO₂ alone. Higher temperature increased the lipid percentage of seed; however, elevated CO₂ reduced the overall lipid content. At the nutrient elements level, whereas elevated CO₂ reduced certain elements, a combination of CO₂ and temperature could compensate for CO₂ reductions but was element dependent.

CONCLUSION

Overall, these data are, at present, the most detailed analysis of rising CO₂ /temperature on the qualitative characteristics of rice. They indicate that climate change is likely to significantly impact the nutritional integrity of rice, with subsequent changes in human health on a global basis. © 2020 Society of Chemical Industry.

Climate Change, Crop Yields, and Grain Quality of C3 Cereals: A Meta-Analysis of [CO2], Temperature, and Drought Effects

Cereal yield and grain quality may be impaired by environmental factors associated with climate change. Major factors, including elevated CO2 concentration ([CO2]), elevated temperature, and drought stress, have been identified as affecting C3 crop production and quality. A meta-analysis of existing literature was performed to study the impact of these three environmental factors on the yield and nutritional traits of C3 cereals. Elevated [CO2] stimulates grain production (through larger grain numbers) and starch accumulation but negatively affects nutritional traits such as protein and mineral content. In contrast to [CO2], increased temperature and drought cause significant grain yield loss, with stronger effects observed from the latter. Elevated temperature decreases grain yield by decreasing the thousand grain weight (TGW). Nutritional quality is also negatively influenced by the changing climate, which will impact human health. Similar to drought, heat stress decreases starch content but increases grain protein and mineral concentrations. Despite the positive effect of elevated [CO2], increases to grain yield seem to be counterbalanced by heat and drought stress. Regarding grain nutritional value and within the three environmental factors, the increase in [CO2] is possibly the more detrimental to face because it will affect cereal quality independently of the region.

Climate Change, Crop Yields, and Grain Quality of C3 Cereals: A Meta-Analysis of [CO2], Temperature, and Drought Effects

Cereal yield and grain quality may be impaired by environmental factors associated with climate change. Major factors, including elevated CO₂ concentration ([CO₂]), elevated temperature, and drought stress, have been identified as affecting C₃ crop production and quality. A meta-analysis of existing literature was performed to study the impact of these three environmental factors on the yield and nutritional traits of C₃ cereals. Elevated [CO₂] stimulates grain production (through larger grain numbers) and starch accumulation but negatively affects nutritional traits such as protein and mineral content. In contrast to [CO₂], increased temperature and drought cause significant grain yield loss, with stronger effects observed from the latter. Elevated temperature decreases grain yield by decreasing the thousand grain weight (TGW). Nutritional quality is also negatively influenced by the changing climate, which will impact human health. Similar to drought, heat stress decreases starch content but increases grain protein and mineral concentrations. Despite the positive effect of elevated [CO₂], increases to grain yield seem to be counterbalanced by heat and drought stress. Regarding grain nutritional value and within the three environmental factors, the increase in [CO₂] is possibly the more detrimental to face because it will affect cereal quality independently of the region.

How do elevated atmosphere CO2 and temperature alter the physiochemical properties of starch granules and rice taste?

Elevated atmospheric CO₂ (EC) and temperature (ET) strongly affect agricultural production, but the mechanism through which EC and/or ET influence starch granules and their relationship to cooked rice taste remain largely unknown. Therefore, a field experiment using a popular japonica cultivar grown in a temperature/free-air CO₂ enrichment environment was conducted to investigate the responses of volume and fine structure of starch granules and their formation physiology to EC (+200 ppm) and/or ET (+1 °C) in 2015-2016. EC markedly enhanced the activity of soluble-starch synthase and granule-bound starch synthase by 28.0% and 27.9% respectively, thereby increasing the long chains and the volume of starch granules. However, EC decreased the activity of starch-branch enzyme by 7.5% possibly via the pathway of ethylene signalling (EC prominently decreased the ethylene evolution rate of rice grains by 28.8%), resulting in a remarkable decrease in α-1'6 glucosidic bonds and significant increase in the iodine-binding capacity and double helix in starch molecules. These EC-induced changes in morphology and fine structure of starch granules synergistically altered the thermal properties of rice flour and eventually improved the cohesiveness and taste of cooked rice, as suggested by the significant relationships between them. ET partially offset the beneficial EC effects in most cases. However, few remarkable CO₂ × temperature or CO₂ × year effects were detected, indicating that the effects of EC on starch granules and rice taste less varied with meteorological conditions. These findings have important implications on rice palatability and for the development of adaptive strategies in the starch industry in future environment.

Response of rice yield traits to elevated atmospheric CO2 concentration and its interaction with cultivar, nitrogen application rate and temperature: A meta-analysis of 20 years FACE studies

The Free Air CO₂ Enrichment (FACE) facility simulates future high CO₂ environment in an open field, and is considered the best approach to assess the actual response of crop production to climate change. This meta-analysis synthesizes all studies conducted under FACE conditions on rice yield response to elevated atmospheric CO₂ concentration ([CO₂]) and its interaction with cultivar, nitrogen application rate and temperature. On average, elevated [CO₂] enhanced rice yield by 16.2%, which resulted from positive response of each yield component. The yield enhancement by elevated [CO₂] of hybrid rice (24.7%) was significantly greater than conventional rice (14.2%), and among conventional rice cultivars, indica rice had a larger yield response (20.4%) than japonica rice (12.7%). The superior performance of hybrid and indica rice under FACE conditions was mainly attributed to the larger increase in spikelet density. The response of rice yield to elevated [CO₂] varied with nitrogen supply. The maximum increase of 21.1% occurred at the nitrogen application rate of 21-30 g m^-2. Both insufficient and excess nitrogen supply negate yield increase by FACE but through different approaches. Elevated [CO₂] increased rice yield by 16.7% at ambient temperature but only 10.1% at elevated temperature (1-2 °C); The smaller yield increase at elevated temperature was due to the negative response of filled grain percentage and grain mass. In conclusion, atmospheric CO₂ concentration projected in the middle of this century will enhance rice yield mainly through the increase of spikelet density, whereas the magnitude of CO₂ fertilizer effect will be affected by the cultivar, nitrogen application rate and temperature.

Influence of elevated CO2 on nutritive value and health-promoting prospective of three genotypes of Alfalfa sprouts (Medicago Sativa)

Alfalfa sprouts are well known for their nutritive values. Although there are several studies reported the positive impact of elevated CO₂ (eCO₂) on plants, there are no in-depth, comprehensive studies on how eCO₂ could improve the sprouting of plant seeds. Herein, the production of health-promoting metabolites was determined in eCO₂ (620 ppm)-treated Alfalfa sprout cultivars (Giza 1, Nubaria and Ismailia 1). eCO₂ increased the photosynthetic process and pigment contents, which consequently induced carbohydrates, proteins, fats and fiber accumulation. eCO₂ also boosted the levels of vitamins, phenolics, flavonoids and mineral individuals and enhanced the antioxidant capacity of alfalfa sprouts. Interestingly, eCO₂ reduced the antinutritional factor l-canavanine content in Ismailia 1 cultivar and improved the anti-inflammatory activities through inhibiting cyclooxygenase-2 and lipoxygenase activity. Therefore, eCO₂ is a promising approach to improve the health-promoting prospective of alfalfa sprouts to be a valuable source of nutritious and bioactive compounds in our daily diet.

Effects of experimental warming on physicochemical properties of indica rice starch in a double rice cropping system

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.

Elevated CO2 and temperature increase grain oil concentration but their impacts on grain yield differ between soybean and maize grown in a temperate region

The increases in CO2 concentration and attendant temperature are likely to impact agricultural production. This study investigated the effects of elevated temperature alone and in combination with CO2 enrichment on grain yield and quality of soybean (Glycine max) and maize (Zea mays) grown in a Mollisol over five-year growing seasons. Plants were grown in open-top chambers with the ambient control, 2.1 °C increase in air temperature (eT) and eT together with 700 ppm atmospheric CO2 concentration (eTeCO2). While eTeCO2 but not eT increased the mean grain yield of soybean by 31%, eTeCO2 and eT increased the yield of maize similarly by around 25% compared to the ambient control. Furthermore, eT and eTeCO2 did not significantly affect grain protein of either species but consistently increased oil concentrations in grains of both species with eTeCO2 increasing more. The eT increased grain Fe concentration relative to the control treatment but decreased Ca concentration, while the relative concentrations of P, K, Mn and Zn varied with crop species. The elevated CO2 enlarged the eT effect on Fe concentration, but decreased the effect on Ca concentration. The results suggest that crop selection is important to maximize yield benefits and to maintain grain quality to cope with elevated CO2 and temperature of future climate change in this temperate region where the temperature is near or below the optimal temperature for crop production.

Changes in grain protein and amino acids composition of wheat and rice under short-term increased [CO2 ] and temperature of canopy air in a paddy from East China

Projected global climate change is a potential threat for food security. Both rising atmospheric CO₂ concentrations ([CO₂ ]) and temperatures have significant impacts on crop productivity, but the combined effects on grain quality are not well understood. We conducted an open-air field experiment to determine the impacts of elevated [CO₂ ] (E-[CO₂ ], up to 500 μmol mol^-1 ) and warming (+2°C) on grain yield, protein and amino acid (AAs, acid digests) in a rice-winter wheat rotation system for 2 yr. E-[CO₂ ] increased grain yield by 11.3% for wheat and 5.9% for rice, but decreased grain protein concentration by 14.9% for wheat and by 7.0% for rice, although E-[CO₂ ] slightly increased the ratio of essential to nonessential AAs. With a consistent decline in grain yield, warming decreased protein yield, notably in wheat, despite a smaller increase in protein concentration. These results indicate that warming could partially negate the negative impact by E-[CO₂ ] on grain protein concentration at the expense of grain yield; this tradeoff could not fully offset the negative effects of climate change on crop production.

Elevated CO2 improves lodging resistance of rice by changing physicochemical properties of the basal internodes

Elevated atmospheric CO₂ concentration has been shown to increase rice yield but its effect on plant lodging resistance is still under debate. In this study, we examined lodging incidence in the field and lodging-related traits of two rice cultivars with contrasting lodging susceptibility under ambient and elevated CO₂ (ca. 200 μmol mol^-1 above ambient) concentrations by using a free-air CO₂ enrichment (FACE) system. Elevated CO₂ (E-CO₂) increased lodging resistance as shown by reduced visual lodging incidence in the field at the late grain filling stage in E-CO₂ plots. This coincided with enhanced in situ pushing resistance of intact plants one week before lodging occurred. The positive CO₂ effect was more pronounced in the lodging-susceptible cultivar LY084. In contrast, the cultivar WYJ23 displayed greater pushing resistance in the field, and no lodging occurred at either ambient or elevated CO₂ conditions throughout the cropping season. The field observations were consistent with the physicochemical characterization of basal internodes of rice plants at the grain filling stage. Greater lodging-resistance of WYJ23 was mainly attributed to its shorter plant height and thicker culm wall of basal internodes. The improvement of lodging resistance by E-CO₂ for the lodging-susceptible cultivar LY084 was mainly related to enhanced culm density, which was explained by elevated starch deposition in the stem. Less lodging incidence under elevated CO₂ contributed to an increase in grain yield by 36% for LY084. In conclusion, rice production could benefit from elevated CO₂ in a changing climate because of an increase in lodging resistance as a result of CO₂-induced improvements in mechanical strength of basal internodes.

Genetic Dissection of qPCG1 for a Quantitative Trait Locus for Percentage of Chalky Grain in Rice (Oryza sativa L.)

Rice is a pivotal cereal crop that provides the staple food for more than half of the world's population. Along with improvements in the standard of living, people not only pay attention to the grain yield but also to the grain quality. Chalkiness is one of the most important index of grain quality. In this study, qPCG1, a QTL for percentage of chalky grain, was mapped in an interval with a physical distance about 139 kb on chromosome 1 by residual heterozygous line (RHL) method. qPCG1 was incomplete dominant and the additive effect plays a major role and explained 6.8-21.9% of phenotypic variance within the heterogeneous region on chromosome 1. The effect of allele from Zhonghui9308 was decreasing the percentage of chalky grains (PCG). Microscope observation results indicated that there are great differences in the shape, structure and arrangement of starch granule between the chalky part and transparent part. Analysis of starch physicochemical properties showed that the total starch content, amylose content and chain length distribution of amylopectin changed while the protein contents were not apparently affected with the changed chalkiness. qPCG1 had little influence on main agronomic traits and it might be useful in rice breeding for it did not bring negative effect on grain yield while reducing the chalkiness.

Do all leaf photosynthesis parameters of rice acclimate to elevated CO2 , elevated temperature, and their combination, in FACE environments?

Leaf photosynthesis of crops acclimates to elevated CO₂ and temperature, but studies quantifying responses of leaf photosynthetic parameters to combined CO₂ and temperature increases under field conditions are scarce. We measured leaf photosynthesis of rice cultivars Changyou 5 and Nanjing 9108 grown in two free-air CO₂ enrichment (FACE) systems, respectively, installed in paddy fields. Each FACE system had four combinations of two levels of CO₂ (ambient and enriched) and two levels of canopy temperature (no warming and warmed by 1.0-2.0°C). Parameters of the C₃ photosynthesis model of Farquhar, von Caemmerer and Berry (the FvCB model), and of a stomatal conductance (g_s ) model were estimated for the four conditions. Most photosynthetic parameters acclimated to elevated CO₂ , elevated temperature, and their combination. The combination of elevated CO₂ and temperature changed the functional relationships between biochemical parameters and leaf nitrogen content for Changyou 5. The g_s model significantly underestimated g_s under the combination of elevated CO₂ and temperature by 19% for Changyou 5 and by 10% for Nanjing 9108 if no acclimation was assumed. However, our further analysis applying the coupled g_s -FvCB model to an independent, previously published FACE experiment showed that including such an acclimation response of g_s hardly improved prediction of leaf photosynthesis under the four combinations of CO₂ and temperature. Therefore, the typical procedure that crop models using the FvCB and g_s models are parameterized from plants grown under current ambient conditions may not result in critical errors in projecting productivity of paddy rice under future global change.

Changes in mineral elements and starch quality of grains during the improvement of japonica rice cultivars

BACKGROUND

The improvement of rice cultivars plays an important role in yield increase. However, little is known about the changes in starch quality and mineral elements during the improvement of rice cultivars. This study was conducted to investigate the changes in starch quality and mineral elements in japonica rice cultivars.

RESULTS

Twelve typical rice cultivars, applied in the production in Jiangsu province during the last 60 years, were grown in the paddy fields. These cultivars were classified into six types according to their application times, plant types and genotypes. The nitrogen (N), phosphorus (P) and, and potassium (K) were mainly distributed in endosperm, bran and bran, respectively. Secondary and micromineral nutrients were distributed throughout grains. With the improvement of cultivars, total N contents gradually decreased, while total P, K and magnesium contents increased in grains. Total copper and zinc contents in type 80'S in grains were highest. The improvement of cultivars enhanced palatability (better gelatinisation enthalpy and amylose content), taste (better protein content) and protein quality (better protein components and essential amino acids). Correlation analysis indicated the close relationship between mineral elements and starch quality.

CONCLUSION

The mineral elements and starch quality of grains during the improvement of japonica rice cultivars are improved. © 2017 Society of Chemical Industry.