A field experiment was conducted to investigate the effects of elevated atmospheric CO2 concentration and temperature, singly and in combination, on grain yield and the distribution of nitrogen (N) in different rice organs. The rice ‘Wuyunjing 23’ was planted under four treatments: ambient CO2 and temperature (ACT), elevated CO2 (200 μmol mol−1 higher than ambient CO2) (EC), elevated temperature (1 °C above the ambient temperature) (ET), and the combination of elevated CO2 and temperature (ECT) under T-FACE (temperature and CO2 free air controlled enrichment) system. CO2-induced increment and temperature-induced reduction in grain yield was 6.0 and 25.2% in 2013, and that was 9.8 and 10.8% in 2014, respectively. Dry matter (DM) production in different organs increased under EC at vegetative stage but decreased under ET at reproductive stage. The negative effects of temperature on grain yield and DM was weakened when combined with CO2 enrichment. And the trends of decrease for yield and DM under ET and ECT in 2013 were more obvious than those in 2014 due to the annual temperature differences. Furthermore, ET led to greater distribution of N in root and stem but not for panicle than that under ACT. These mainly demonstrated that the rice production would be suffered varying degree of loss under global warming in future although the CO2 enrichment could alleviate the effects of high temperature on rice growth.

Effects of elevated ozone concentrations [O3] on two wheat (Triticum aestivum L.) cultivars [Yangmai16 (Y16) and Yannong19 (Y19)] were investigated to determine the different metabolic mechanisms of phenolic compounds under O3-FACE (free-air controlled enrichment) condition. This study specifically investigated changes of phenolic compounds content, secondary metabolism related enzymes activities, lipid peroxidation extent and reactive oxygen species (ROS) content in the leaves of two wheat cultivars. Results indicated that elevated [O3] (1.5 × ambient [O3]) induced different regulation mechanisms of secondary metabolism in different wheat cultivars. Lipid peroxidation and ROS content increased under O3 stress, and these results were more pronounced in the leaves of Y19 than in those of Y16, suggesting that Y19 is more sensitive to O3 than Y16.

Elevated CO2 levels and the increase in heavy metals in soils through pollution are serious problems worldwide. Whether elevated CO2 levels will affect plants grown in heavy-metal-polluted soil and thereby influence food quality and safety is not clear. Using a free-air CO2 enrichment (FACE) system, we investigated the impacts of elevated atmospheric CO2 on the concentrations of copper (Cu) or cadmium (Cd) in rice and wheat grown in soil with different concentrations of the metals in the soil. In the two-year study, elevated CO2 levels led to lower Cu concentrations and higher Cd concentrations in shoots and grain of both rice and wheat grown in the respective contaminated soil. Elevated CO2 levels slightly but significantly lowered the pH of the soil and led to changes in Cu and Cd fractionation in the soil. Our study indicates that elevated CO2 alters the distribution of contaminant elements in soil and plants, thereby probably affecting food quality and safety.

Rice (a C3 crop) and barnyard grass (Echinochloa crusgalli L.) (a C4 weed) were grown in a 1:1 mixture in a paddy field in ambient condition and with supplemented free air carbon dioxide enrichment (FACE, CO2 concentration + 200 μmol mol−1), in order to evaluate the impact of rising atmospheric carbon dioxide on nutrient competition between rice crop and weed. Results showed that elevated CO2 significantly enhanced the biomass, tillers, leaf area index (LAI) and net assimilation rate (NAR) of rice, but reduced those of barnyard grass after elongation. Tissue nitrogen (N) concentrations were decreased in both competitors, but their phosphorus (P) and potassium (K) concentration were increased. The increase in tissue P concentration of rice was greater than that in barnyard grass. Furthermore, the absolute uptake of C, N, P, K by rice were increased while those of barnyard grass decreased. As a result, significant increase of the ratios of rice/barnyard grass of biomass and absolute nutrient uptake were observed under elevated CO2. The results suggest that rising atmospheric CO2 concentration could alter the competition between rice and barnyard grass in paddy fields in favor of rice. The ability of rice to compete more successfully for nitrogen and phosphorous under elevated CO2 is likely an important factor underlying this response. More generally, the results suggest that elevated CO2 may have varying implications on nutrient dynamics between different elements of overall plant biomass and the soil nutrients pool.

Soil respiration in a cropland is the sum of heterotrophic (mainly microorganisms) and autotrophic (root) respiration. The contribution of both these types to soil respiration needs to be understood to evaluate the effects of environmental change on soil carbon cycling and sequestration. In this paper, the effects of free-air CO2 enrichment (FACE) on hetero- and autotrophic respiration in a wheat field were differentiated and evaluated by a novel split-root growth and gas collection system. Elevated atmospheric pCO2 of approximately 200 μmol mol−1 above the ambient pCO2 significantly increased soil respiration by 15.1 and 14.8% at high nitrogen (HN) and low nitrogen (LN) application rates, respectively. The effect of elevated atmospheric pCO2 on root respiration was not consistent across the wheat growth stages. Elevated pCO2 significantly increased and decreased root respiration at the booting-heading stage (middle stage) and the late-filling stage (late stage), respectively, in HN and LN treatments; however, no significant effect was found at the jointing stage (early stage). Thus, the effect of increased pCO2 on cumulative root respiration for the entire wheat growing season was not significant. Cumulative root respiration accounted for approximately 25–30% of cumulative soil respiration in the entire wheat growing season. Consequently, cumulative microbial respiration (soil respiration minus root respiration) increased by 22.5 and 21.1% due to elevated pCO2 in HN and LN, respectively. High nitrogen application significantly increased root respiration at the late stage under both elevated pCO2 and ambient pCO2; however, no significant effects were found on cumulative soil respiration, root respiration, and microbial respiration. These findings suggest that heterotrophic respiration, which is influenced by increased substrate supplies from the plant to the soil, is the key process to determine C emission from agro-ecosystems with regard to future scenarios of enriched pCO2.

The responses of rice to the second degree contamination of copper were studied by pot experiments under free-air CO2 enrichment (FACE) with 570 μmol·mol−1 of CO2. The results showed that the content of copper in rice leaves was reduced with the CO2 concentration reaching 570 μmol·mol−1 and this happened more significantly under the second degree contamination of copper. Under FACE, activities of superoxide dismutase (SOD) enzyme in rice leaves treated by copper contamination were induced, whereas the contents of glutathione (GSH) and glutathione disulfide (GSSG) had no significant difference from the control. In the presence of ambient CO2, activities of SOD enzyme treated by copper pollution were suppressed during the whole rice growth, however, the contents of GSH and GSSG were induced at tillering and jointing stages, and then restored to the control levels in later growth under the second degree contamination of copper. With the rice growing, the content of malondialdehyde (MDA) rises continuously, but there had been no significant difference between the treatments at the same growth stage. Further studies are needed on the response mechanism of rice to Cu stress under elevated CO2.

Free-air CO2 enrichment (FACE) system at a Chinese rice–wheat rotation field was constructed to investigate responses of rice and wheat crop growth to elevated CO2 and nitrogen fertilization. A factorial experiment design was set up with two levels of atmospheric CO2 concentration (350 and 550 μmol mol−1) and N application rates (LN: 150 kg N ha−1 for rice and 125 kg N ha−1 for wheat; HN: 250 kg N ha−1 for rice and wheat, respectively). Across the entire crop growing seasons, plant fractions (i.e. leaf, stem, ear and root) were differentiated at representative growth stages and analyzed using widely recognized parameters, relative growth rate (RGR) and allometric coefficient Ka (RGR ratio of above ground to below ground plant biomass). The C/N ratio and phosphorus concentration of plant were also determined. Rice and wheat RGRs responded to elevated CO2 in different ways, i.e. wheat RGR was always stimulated by elevated CO2 while rice RGR seemed to be depressed between rice tillering to jointing stages. Elevated CO2 affected the plant fractions differentially. For example, rice leaf might be the most strongly affected organ by RGR analysis and by Ka analysis it seems that elevated CO2 always led to higher below ground biomass (root) than above ground biomass. Besides, elevated CO2 usually resulted in a higher C/N ratio of plant due to its impact on N concentration instead of carbon. Regardless of CO2 treatment statistic analysis of rice and wheat RGR did not yield significant difference in plant growing patterns under LN and HN treatments, although LN always triggered a slightly higher C/N ratio of plant over the investigated period. Furthermore, it was generally observed that elevated CO2 could stimulate crop biomass to a greater extent under LN treatment than HN treatment. Phosphorus concentration of rice and wheat crop showed distinctive response to elevated CO2 and N constraint.

Studies on the effect of elevated CO2 on C dynamics in cultivated croplands are critical to a better understanding of the C cycling in response to climate change in agroecosystems. To evaluate the effects of elevated CO2 and different N fertilizer application levels on soil respiration, winter wheat (Triticum aestivum L. cv. Yangmai 14) plants were exposed to either ambient CO2 or elevated CO2 (ambient [CO2] + 200 μmol mol−1), under N fertilizer application levels of 112.5 and 225 kg N ha−1 (as low N and normal N subtreatments, respectively), for two growing seasons (2006–2007 and 2007–2008) in a rice-winter wheat rotation system typical in China. A split-plot design was adopted. A root exclusion method was used to partition soil respiration (RS) into heterotrophic respiration (RH) and autotrophic respiration (RA).Atmospheric CO2 enrichment increased seasonal cumulative RS by 11.8% at low N and 5.6% at normal N when averaged over two growing seasons. Elevated CO2 significantly enhanced (P < 0.05) RS (12.7%), mainly due to the increase in RH (caused by decomposition of larger amounts of rice residue under elevated CO2) during a relative dry season in 2007–2008. Higher N supply also enhanced RS under ambient and elevated CO2. In the 2007–2008 season, normal N treatment had a significant positive effect (P < 0.01) on seasonal cumulative RS relative to low N treatment when averaged across CO2 levels (16.3%). A significant increase in RA was mainly responsible for the enhanced RS under higher N supply. The correlation (r2) between RH and soil temperature was stronger (P < 0.001) than that between RS and soil temperature when averaged across all treatments in both seasons. Seasonal patterns of RA may be more closely related to the plant phenology than soil temperature. The Q10 (the multiplier to the respiration rate for a 10 °C increase in soil temperature) values of RS and RH were not affected by elevated CO2 or higher N supply. These results mainly suggested that the increase in RS at elevated CO2 depended on the input of rice residue, and the increase in RS at higher N supply was due to stimulated root growth and concomitant increase in RA during the wheat growing portion of a rice-winter wheat rotation system.

An experiment with the free-air carbon dioxide enrichment (FACE) method was conducted in a paddy field at Wuxi (Jiangsu Province, China) to study effects of elevated atmospheric [CO2] on availability of soil nitrogen and phosphorus. Rice (Oryza sativa L.) and winter wheat (Triticum aestivum L.) were grown under ambient CO2 or FACE (ambient + 200 μmol mol−1 CO2) conditions throughout the growth season. Low N (LN) and normal N (NN) were applied, LN being 150 kg ha−1 for rice and 125 kg ha−1 for wheat and NN being 250 kg ha−1 for both rice and wheat.Compared with the ambient [CO2] condition, elevated [CO2] significantly increased crop biomass and P uptake for both rice and wheat and N uptake only for wheat at several main growth stages. The positive effects of elevated [CO2] on biomass, N and P uptake of wheat were greater than of rice.Soil available N was decreased by elevated [CO2] by 47% in LN and 29% in NN at the rice tillering stage at jointing stage and decreased by 25.4% and 28.3% in LN and by 33.3% and 53.1% in NN at the wheat seeding and heading stages, respectively. Soil available P was decreased by elevated [CO2] in rice by 32.0% in LN and by 29.6% in NN at the jointing stage, but increased by 22.4% and 20.8% at the heading stage and by 33.8% and 30.7% at the ripening stage in LN and NN, respectively. While in the wheat season, soil available P was not affected significantly by elevated [CO2] at each stage.These results suggest that under elevated [CO2] availability of soil N and P increased, particularly P and application of N and P should be adjusted to need for rice at tillering and jointing and for wheat at whole growth stages.

Rising tropospheric ozone concentrations ([O3]) can lead to considerable damage to agricultural crops. Experimental data have shown that the relationship between O3 injury and yield loss differs with crop species and that O3 sensitivity differs among cultivars of the same species. To explore a breeding strategy to adapt crops to high [O3], it is necessary to investigate the different mechanisms for cultivar resistance to O3 stress. Although several chamber-based studies have examined antioxidant defence differences in rice (Oryza sativa L.) cultivars in response to elevated [O3], such as the utilisation of the ascorbate–glutathione (AsA–GSH) cycle to eliminate reactive oxygen species (ROS), little research has been conducted under free-air O3 enrichment (O3-FACE) to address the different AsA–GSH cycle responses of rice cultivars. In this experiment, O3-FACE was used to investigate the AsA–GSH cycle in two rice cultivars, SY63 (O3-sensitive) and WXJ14 (O3-resistant). The results indicated that, compared with the ambient [O3], elevated [O3] (1.5 × ambient [O3]) induced increases in the superoxide anion (O2−) production rate, hydrogen peroxide (H2O2) content, malondialdehyde (MDA) content and relative electrical conductivity; increases that were greater in SY63 than in WXJ14. Continuous O3 stress also resulted in a less efficient metabolism of the AsA–GSH cycle in SY63 compared to WXJ14. The results indicated that in SY63, elevated [O3] accelerated ROS metabolism rates, and the antioxidant system could not prevent oxidative damage, thus increasing membrane lipid peroxidation. In contrast, in WXJ14, there was transient damage in response to elevated [O3] early in the sampling period, which triggered the ROS to stimulate the antioxidant system to avoid O3 stress. Our results suggested that ROS detoxification by the AsA–GSH cycle under long-term exposure to an O3-enriched atmosphere plays a more important role in an O3-resistant rice cultivar than in an O3-sensitive rice cultivar and that a better understanding of antioxidant system mechanisms is essential to the assessment of different rice cultivars’ responses to future tropospheric [O3].Highlights► We applied O3-FACE to investigate antioxidant system in rice. ► We chose two rice cultivars, which had different O3 sensitivity. ► Continuous O3 resulted in lower efficiency of AsA–GSH cycle in SY63 than WXJ14. ► ROS as a signal stimulated antioxidant system to protect WXJ14.

Rising tropospheric ozone concentration is currently the most important air pollutant which suppresses plant growth and thus results in yield loss of agronomic crops. However little is known about ozone effects on grain quality of crops. Using a free-air gas concentration enrichment (FACE) facility for ozone fumigation in paddy rice (Oryza Sativa L.), a Chinese hybrid indica cultivar Shanyou 63 was exposed to either ambient or elevated ozone concentration (ca 23.5% above ambient) for two consecutive growth seasons from 2007 to 2008. Harvested grain samples were subjected to various quality tests. In both seasons, the brown, milled and head rice yield all reduced by elevated ozone concentration, with this reduction being greater in 2008 (17–22%) than in 2007 (8–19%). Ozone elevation caused small but significant decrease in brown rice percentage, but greatly increased head rice percentage by 8.8%. Chalky grain percentage increased (5.8%) due to ozone elevation, while chalkiness area and chalkiness degree remaining unchanged. Although the amylose concentration of rice grains was marginally reduced, starch pasting properties demonstrated that grains in elevated ozone concentration had lower breakdown (7.7%) and higher setback value (25.2%) and gelatinization temperature (0.9 °C) than those grown in ambient conditions. Nutrition evaluation indicated that ozone exposure tended to increase the concentrations of protein and all mineral elements analyzed (i.e., K, Mg, Ca, Fe, Zn, Mn and Cu), but the contents of protein and mineral elements in harvested grains were unchanged or reduced. For most traits of grain quality, the year effect was significant, however, its interaction with ozone was not detected. Our results suggested that long-term exposure to ozone-enriched atmospheres projected in the coming a few decades not only caused serious reductions in yield, but also tended to produce the deleterious effects upon grain quality of hybrid Shanyou 63 in terms of appearance and eating/cooking quality.Highlights► The impacts of projected future levels of tropospheric ozone concentration on grain quality of hybrid rice cultivar Shanyou 63 were determined under fully open-air field conditions. ► Ozone exposure enhanced the formation of chalky grains, while increased the head rice percentage. ► Elevated ozone concentration decreased eating and cooking quality of rice, but had positive influence on nutritive value of rice.