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Assessments of the impacts of ozone (O3) on regional and global food production are currently based on results from experiments using open-top chambers (OTCs). However, there are concerns that these impact estimates might be biased due to the environmental artifacts imposed by this enclosure system. In this study, we collated O3 exposure and yield data for three major crop species--wheat, rice, and soybean--for which O3 experiments have been conducted with OTCs as well as the ecologically more realistic free-air O3 elevation (O3-FACE) exposure system; both within the same cultivation region and country. For all three crops, we found that the sensitivity of crop yield to the O3 metric AOT40 (accumulated hourly O3 exposure above a cut-off threshold concentration of 40 ppb) significantly differed between OTC and O3-FACE experiments. In wheat and rice, O3 sensitivity was higher in O3-FACE than OTC experiments, while the opposite was the case for soybean. In all three crops, these differences could be linked to factors influencing stomatal conductance (manipulation of water inputs, passive chamber warming, and cultivar differences in gas exchange). Our study thus highlights the importance of accounting for factors that control stomatal O3 flux when applying experimental data to assess O3 impacts on crops at large spatial scales. [ABSTRACT FROM AUTHOR]

A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 ( eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in free-air CO2 enrichment ( FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) in all three ecosystem types, this relationship was positive, linear and strong ( r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. As the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial timescale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation. [ABSTRACT FROM AUTHOR]

We investigated the effects of elevated ozone concentration (E-O3) on CH4 and N2O emission from paddies with two rice cultivars: an inbred Indica cultivar Yangdao 6 ( YD6) and a hybrid one II-you 084 ( IIY084), under fully open-air field conditions in China. A mean 26.7% enhancement of ozone concentration above the ambient level (A-O3) significantly reduced CH4 emission at tillering and flowering stages leading to a reduction of seasonal integral CH4 emission by 29.6% on average across the two cultivars. The reduced CH4 emission is associated with O3-induced reduction in the whole-plant biomass (−13.2%), root biomass (−34.7%), and maximum tiller number (−10.3%), all of which curbed the carbon supply for belowground CH4 production and its release from submerged soil to atmosphere. Although no significant difference was detected between the cultivars in the CH4 emission response to E-O3, a larger decrease in CH4 emission with IIY084 (−33.2%) than that with YD6 (−7.0%) was observed at tillering stage, which may be due to the larger reduction in tiller number in IIY084 by E-O3. Additionally, E-O3 reduced seasonal mean NOx flux by 5.7% and 11.8% with IIY084 and YD6, respectively, but the effects were not significant statistically. We found that the relative response of CH4 emission to E-O3 was not significantly different from those reported in open-top chamber experiments. This study has thus confirmed that increasing ozone concentration would mitigate the global warming potential of CH4 and suggested consideration of the feedback mechanism between ozone and its precursor emission into the projection of future ozone effects on terrestrial ecosystem. [ABSTRACT FROM AUTHOR]

By using a free-air controlled enrichment (FACE) system, this paper studied the effects of elevated atmospheric ozone (O3) concentration (150% of ambient O3) on the flag leaf photosynthetic pigment contents of wheat varieties Yannong 19, Yangmai 16, Jiaxin 002, Yangmai 15, and Yangfumai 2. For the test varieties, no significant differences were observed in the flag leaf chlorophyll a, chlorophyll b, chlorophyll (a+b), and carotenoid contents between treatments elevated O3 concentration and ambient O3 at booting and anthesis stages, but the photosynthetic pigment contents in treatment elevated O3 concentration all decreased after anthesis, with a significant decrease of chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents, which indicated that elevated O3 had minor effects on the synthesis of photosynthetic pigments but accelerated their decline process. Different wheat varieties had genetic difference in the responses of flag leaf photosynthetic pigment contents to elevated O3, among which, Yangmai 15 and Jiaxin 002 had better tolerance to ozone stress. The flag leaf chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents at grain-filling stage (about 21 days after anthesis) had a significant positive correlation with the 1000-grain mass. [ABSTRACT FROM AUTHOR]

By using FACE (Free-Air Controlled Environment)-ozone system, a field plot experiment was conducted in 2008-2009 to study the effects of elevated ozone (O3) concentration on the flag leaf microscopic structure, chlorophyll content, and grain weight of wheat. Two treatments were installed, i. e. , ambient O3 and 150% of ambient O3, and four winter varieties, i. e. , Yannong 19, Yangmai 16, Jiaxin 002, and Yangfumai 2, were taken as the test materials. At anthesis, elevated O3 concentration had a slight damage to the flag leaf microscopic structure. The mesophyll cell and chloroplast structure began destroying, and the grana lamellae started breaking and loosing. Twenty-one days after anthesis, the differences in the leaf microscopic structure between the two treatments became significant. Under elevated O3, the flag leaf senescence was accelerated, with the endomembrane system disintegrated, grana lamella disappeared, and corpus adiposum inside chloroplast broken down, resulting in a significant decrease of the chlorophyll content, photosynthesis rate, and grain weight at maturing stage. Significant difference was observed among the test varieties in their responses to elevated O3. Jiaxin 002 was tolerant, while Yangfumai 2 was sensitive to the ozone stress. [ABSTRACT FROM AUTHOR]

Over time, the relative effects of elevated [CO2] on the aboveground photosynthesis, growth and development of rice ( Oryza sativa L.) are likely to be changed with increasing duration of CO2 exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO2] on seasonal changes in root growth, morphology and physiology of rice, a free-air CO2 enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002–2003. A japonica cultivar with large panicle was exposed to two [CO2] (ambient [CO2], 370 μmol mol−1; elevated [CO2], 570 μmol mol−1) at three levels of nitrogen (N): low (LN, 15 g N m−2), medium (MN, 25 g N m−2) and high N (HN, 35 g N m−2). Elevated [CO2] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25–71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO2] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO2] during MGP and LGP, the decline being larger during MGP than LGP. The CO2-induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO2-induced increases in shoot growth of rice are similarly associated with increased root growth. [ABSTRACT FROM AUTHOR]

Recent research suggests that rice root characteristics, particularly growth, are altered by elevated atmospheric CO2. Thus, microbial communities existing in or on rice roots could be greatly influenced by atmospheric CO2 concentration. We investigated the effect of elevated atmospheric CO2 on ammonia oxidizing bacteria (AOB) communities associated with rice roots using polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing methods. Rice roots were collected from rice fields in a free-air CO2 enrichment experiment at Shizukuishi, Japan. Differences in DGGE banding patterns among elevated atmospheric CO2 and ambient treatments, young and old roots and rice growth stages were evident. Principal component analysis indicated that AOB communities in rice roots were influenced mainly by rice growth stage, although there was a tendency for communities from elevated CO2 conditions to be different from communities under ambient conditions. Both Nitrosospira-like and Nitosomonas-like AOB sequences were detected in the rice roots tested. Close relatives of Nitrosospira sp. NpAV strain were likely to be the most dominant AOB inhabiting rice roots in the experimental paddy field. Although the DGGE band patterns showed a possible difference between ambient and elevated CO2, under both CO2 levels the bands that were sequenced were predominately Nitrosospira spp. with AmoA clusters 1 and 2. [ABSTRACT FROM AUTHOR]

An anaerobic incubation experiment was conducted to investigate methane (CH4) production potential in soil samples collected from a paddy field after exposure to free-air CO2 enrichment (FACE). The FACE experiment with two CO2 levels, ambient and ambient + 200 p.p.m.v CO2 during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0–1 cm) and the sub-surface (1–10 cm) soil layers 2 months after rice harvest. Sub-samples of the fresh soils were put into glass bottles and submerged under N2 gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH4 production potential was approximately 2–4-fold higher in FACE soil than ambient soil and approximately 500–1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted long-term positive effects on CH4 production and increased organic C content in this paddy soil, particularly in the surface soil layer. [ABSTRACT FROM AUTHOR]

An increase in atmospheric CO2 concentration ( [CO2]) is generally expected to enhance photosynthesis and biomass. Rice plants (Oryza sativa L.) were grown in ambient CO2 (AMB) or free-air CO2-enrichment (FACE), in which the target [CO2] was 200 µmol mol–1 above AMB. 13CO2 was fed to the plants at different stages so we could examine the partitioning of photosynthates. Furthermore, canopy photosynthesis and respiration were measured at those stages. The ratio of 13C content in the whole plant to the amount of fixed 13C under FACE was similar to that under AMB at the vegetative stage. However, the ratio under FACE was greater than the ratio under AMB at the grain-filling stage. At the vegetative stage, plants grown under FACE had a larger biomass than those grown under AMB owing to enhancement of canopy photosynthesis by the increased [CO2]. On the other hand, at the grain-filling stage, CO2 enrichment promoted the partitioning of photosynthate to ears, and plants grown under FACE had a greater weight of ears. However, enhancement of ear weight by CO2 enrichment was not as great as that of biomass at the vegetative stage. Plants grown under FACE did not necessarily show higher canopy photosynthetic rates at the grain-filling stage. Therefore, we concluded that the ear weight did not increase as much as biomass at the vegetative stage owing to a loss of the advantage in CO2 gain during the grain-filling period. [ABSTRACT FROM AUTHOR]

Using free-air CO2 enrichment (FACE) we grew rice crops at ambient or elevated (ca. 250 μmol mol-1 above ambient) and evaluated soil nutrition status by determining the elemental composition of soil solution. The dry matter of rice was increased by elevated CO2. Although the increase in dry matter after panicle initiation was greater in rice grown with FACE than in rice grown in ambient CO2, the increase rate was lower after panicle initiation. The nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) concentrations of rice were significantly 21, 6, 14, and 9% lower, respectively, in rice grown with FACE than the concentrations in ambient grown rice at panicle initiation, and the N and K concentrations were significantly lower with FACE at harvest. Although the N and K uptakes of rice were higher with FACE than in ambient grown rice at panicle initiation, the differences were small after panicle initiation. The ammonium, phosphate, K, and silicate concentrations in soil solution gradually decreased before panicle initiation. The relation between the N and K uptake of rice and the concentrations in soil solution indicated the N and K supply from soil regulated the uptake after the concentrations were decreased in soil solution. The N uptake of rice appeared to be determined by the soil N availability, not by nutrition demand and uptake ability of rice after panicle initiation, and the amount of N uptake seemed to limit rice growth. [ABSTRACT FROM AUTHOR]

Abstract Over time, the stimulative effect of elevated CO2 on the photosynthesis of rice crops is likely to be reduced with increasing duration of CO2 exposure, but the resultant effects on crop productivity remain unclear. To investigate seasonal changes in the effect of elevated CO2 on the growth of rice (Oryza sativa L.) crops, a free air CO2 enrichment (FACE) experiment was conducted at Shizukuishi, Iwate, Japan in 1998–2000. The target CO2 concentration of the FACE plots was 200 µmol mol-1 above that of ambient. Three levels of nitrogen (N) were supplied: low (LN, 4 g N m-2 ), medium [MN, 8 (1998) and 9 (1999, 2000) g N m-2 ] and high N (HN, 12 and 15 g N m-2 ). For MN and HN but not for LN, elevated CO2 increased tiller number at panicle initiation (PI) but this positive response decreased with crop development. As a result, the response of green leaf area index (GLAI) to elevated CO2 greatly varied with development, showing positive responses during vegetative stages and negative responses after PI. Elevated CO2 decreased leaf N concentration over the season, except during early stage of development. For MN crops, total biomass increased with elevated CO2 , but the response declined linearly with development, with average increases of 32, 28, 21, 15 and 12% at tillering, PI, anthesis, mid-ripening and grain maturity, respectively. This decline is likely to be due to decreases in the positive effects of elevated CO2 on canopy photosynthesis because of reductions in both GLAI and leaf N. Up to PI, LN-crops tended to have a lower response to elevated CO2 than MN- and HN-crops, though by final harvest the total biomass response was similar for all N levels. For MN- and HN-crops, the positive response of grain yield (ca. 15%) to elevated CO2 was slightly greater than the response of final total biomass while for LN-crops it was less. We conclude that most of the seasonal changes in crop response to elevated CO2 are directly or indirectly associated with N uptake. [ABSTRACT FROM AUTHOR]

As part of a FACE (free-air CO2 enrichment) experiment in a rice paddy field in Shizukuishi (Iwate Prefecture, Japan), studies were conducted to determine the effects of elevated CO2 on N dynamics at three levels of N application. Rice plants were grown under ambient CO2 or ambient + 200 ppmV CO2 conditions throughout the growing season in an Andosol soil with each treatment having 4 replicated plots. Three levels of N fertilizer (high, standard and low; 15, 9 and 4 gN m−2, respectively) were applied to examine different N availability under both CO2 conditions. Soil samples were collected at 4 different times from upper and lower soil layers (0–1 cm and 1–10 cm soil depths, respectively) and analyzed for microbial biomass N (BN), mineralizable N (Min. N) and NH4 +-N in soil. Plant sampling was also done at 3 different times during the growing season to determine the N uptake by plant. Elevated CO2 significantly increased BN and Min. N in the upper soil layer at harvest by 25–42% and 18–24%, respectively, compared to ambient CO2, regardless of N application rate. In low N soil, these significant increases were also observed at the ripening stage. In addition, elevated CO2 only significantly increased the NH4 +-N in the upper soil layer at harvest in low N soil compared to ambient CO2. The N uptake was not significantly affected by CO2 treatment. These results indicate that elevated CO2 had significant positive influence on BN and Min. N in the upper soil layer in paddy soil at the later period of the cropping season at all levels of N application rates, but only at low levels of application rate on NH4 +-N. [ABSTRACT FROM AUTHOR]

Although the projected increases in global atmospheric CO2 levels are expected to lead to greater yields, little is known about the effects of elevated CO2 on the grain nutrient concentrations of staple food crops such as rice (Oryza sativa L.). Large changes could have potential implications for the micro-elemental nutrition of populations where these grains provide a large proportion of the dietary needs. The limited data on the effects of elevated CO2 on grain elemental concentrations is derived from plants growing in pots placed in environmental enclosures: these indicate that elevated CO2 can cause large decreases in grain elemental concentrations. In view of the lack of data from field-grown plants, we analysed the elemental concentrations of archived grain samples collected from temperate rice crops grown under free-air CO2 enrichment (FACE) conditions. Like in the pot experiments, in our study elevated CO2 increased biomass and grain production and decreased grain N concentrations. In contrast however, we found no changes in the concentrations of any of the other elements analysed. We thought it is likely that dilution was observed in the pot studies because nutrient supplies were limiting, primarily because of the small rooting volumes. In contrast, our experiment was conducted under field conditions, with highly fertile soils and large rooting volumes leading to plentiful nutrient supplies (especially micro-elements). The root production response under elevated CO2 was more than twice the aboveground biomass response; we hypothesised that if this led to a greater relative nutrient uptake capacity, elemental uptake may have matched the increase in aboveground biomass and hence no change in concentration would be detected. We conclude that a dilution of elements in the grain is not a foregone conclusion under elevated CO2: where elements are in plentiful supply and uptake rates can match increases in yield, no dilution will be detected. However, because elemental levels in most agro-ecosystems are usually less than in our experiment, some dilution is likely to occur, but to a lesser extent than that found in pot experiments where nutrient dilution is likely to be common phenomena. [Copyright &y& Elsevier]

A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 ( eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in free-air CO2 enrichment ( FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) in all three ecosystem types, this relationship was positive, linear and strong ( r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. As the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial timescale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A system for free-air concentration enrichment with ozone (FACE-O3) was installed in a field in Jiangsu Province of China to grow wheat and rice plants in either ambient [O3] (A-O3) or elevated [O3] (E-O3) without any enclosures. Ozone generated from pure O2 and mixed with compressed air was released into the E-O3 plots from a 14 m diameter octagon. The gas release was controlled for each E-O3 plot with an algorithm based on wind direction, wind speed and [O3] at the center of the plot. With 1-min mean [O3], the achieved elevation was within ±20% of the target, which is 50% above A-O3, for 94% of time, and within ±10% of the target for 73% of time on average across 4 years from 2007 to 2010. Ozone fumigation ran on daytime, but was withheld when ambient [O3] was below 20 ppb or leaves were wet. The discontinuity in O3 release resulted in the daily mean 7 h [O3] (M7, 900–1600 h Chinese Standard Time) in E-O3 by only 24% higher than that in A-O3. The average effective increase in AOT40 (accumulated [O3] above the threshold of 40 ppb) was 115%. Ozone exposure regime in E-O3 as characterized by M7 and AOT40 was compared with that in a scaled-up [O3] (S-O3), which was obtained by scaling A-O3 by 1.24: the ratio of M7 in E-O3 to that in A-O3. For the same M7, E-O3 had higher AOT40 than S-O3, because E-O3 had more high [O3] peaks than S-O3. The shift in AOT40 is only modest, however, and the [O3] regime in E-O3 was consistent with that in open-top chamber experiments in the past. This FACE-O3 system can thus maintain elevated [O3] in open field with modest alteration to [O3] regime to an extent comparable to open-top chambers. [Copyright &y& Elsevier]

Abstract: Increasing global atmospheric CO2 concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO2 (AMB) or free-air CO2-enrichment (FACE) at CO2 concentrations ranged from 275 to 365μmolmol−1 above AMB. We supplied 13CO2 to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with 13C at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem 13C content. Furthermore, there were no differences between treatments in whole-plant 13C contents at heading and grain maturity. In contrast, plants supplied with 13C at the grain-filling stage had more 13C in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO2 enrichment might be effectively stored in the grains. Furthermore, regardless of when the 13C was supplied, plants had more 13C in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO2 enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains. [Copyright &y& Elsevier]