A Preliminary Study of the Impacts of Duckweed Coverage during Rice Growth on Grain Yield and Quality.

The overuse and misuse of fertilizers have been causing duckweed outbreaks in irrigation ditches and paddy fields in many rice-growing areas. However, how duckweed coverage in a paddy field affects the rice yield and grain quality is under debate because duckweed may act as either a weed, competing with rice for mineral nutrients, or a "nutrient buffer", providing significant ecological and economic benefits. To understand the effects of duckweed coverage throughout rice growth on the yield and quality of rice grains, an experiment with three Japonica rice cultivars was conducted with fertile lotus-pond bottom soil as a growth medium to provide sufficient mineral nutrients for both the duckweed and rice. Averaged across three rice cultivars, duckweed coverage decreased the panicle density but increased the spikelet density and grain weight, resulting in no significant change in the rice yield. Duckweed coverage had no impact on the processing and appearance quality in general, but significant duckweed-by-cultivar interactions were detected in the head rice percentage and grain chalkiness, indicating different sensitivities of different cultivars in response to the duckweed treatment. The decrease in breakdown and increase in setback values in the rapid visco analyzer (RVA) profile of rice flour suggested that duckweed coverage during rice growth worsened the cooking quality of the rice. However, no significant change in the palatability of the cooked rice was found. The most profound change induced by the duckweed was the nutritional quality; duckweed coverage increased the protein concentration but decreased the concentrations of Mg, Mn, Cu, and Zn in rice grains. This preliminary study suggested that duckweed coverage during rice growth has profound effects on the rice nutrient uptake and grain nutritional quality under the circumstances, and further research on the responses of the rice quality to the duckweed coverage in paddy fields in multiple locations and years is needed.

Response of rice growth and leaf physiology to elevated CO2 concentrations: A meta-analysis of 20-year FACE studies.

The Free Air CO2 Enrichment (FACE) facility enables the study of plant responses to climate change under open field conditions. This meta-analysis was conducted to quantitatively assess the effects of elevated CO2 concentration ([CO2]) on 47 variables describing rice growth physiology and whether CO2 effects were influenced by cultivar, plant growth stage, nitrogen application rate or temperature. On average, elevated [CO2] increased root and shoot biomass by 28% and 19%, respectively. Among shoot organs, the [CO2]-induced increase in leaf biomass was only 9%, significantly smaller than a 24% increase in stems or a 25% increase in panicles. The higher biomass for FACE rice was consistent with the stimulation in plant height (4%), maximum tiller number (11%), leaf area index (9%) and light-saturated photosynthetic rate (Asat, 22%). When compared within rice groups, hybrid rice showed the greatest CO2 response in growth and leaf physiological variables. Elevated [CO2] increased plant biomass and Asat at each rice growth stage, but the increment tended to decline with the advancement of rice growth and development. The increase in aboveground biomass at elevated [CO2] was enhanced by a higher nitrogen supply but reduced with a temperature elevation of 1-2 °C. Rice growth benefited more from elevated [CO2] in Chinese FACE studies than in Japanese FACE studies, which may result from the different cultivars and nitrogen application rates used in the two countries. Combined with a previous meta-analysis of the rice yield response to FACE, the [CO2] level predicted in the middle of this century will improve rice productivity by stimulating leaf photosynthesis. However, the effects of CO2 on the photosynthetic rate and rice growth tend to shrink over the plant life cycle. Selecting heat-resistant, high-yield hybrid rice cultivars with large sink capacity, supplemented with appropriate nitrogen input, will maximize the CO2 fertilizer effect in the future.

Alterations in Source-Sink Relations Affect Rice Yield Response to Elevated CO2: A Free-Air CO2 Enrichment Study.

To understand the effects of source-sink relationships on rice yield response to elevated CO2 levels (eCO2), we conducted a field study using a popular japonica cultivar grown in a free-air CO2 enrichment environment in 2017-2018. The source-sink ratio of rice was set artificially via source-sink treatments (SSTs) at the heading stage. Five SSTs were performed in 2017 (EXP1): cutting off the flag leaf (LC1) and the top three functional leaves (LC3), removing one branch in every three branches of a panicle (SR1/3) and one branch in every two branches of a panicle (SR1/2), and the control (CK) without any leaf cutting or spikelet removal. The eCO2 significantly increased grain yield by 15.7% on average over all treatments; it significantly increased grain yield of CK, LC1, LC3, SR1/3, and SR1/2 crops by 13.9, 18.1, 25.3, 12.0, and 10.9%, respectively. The yield response to eCO2 was associated with a significant increase of panicle number and fully-filled grain percentage (FGP), and the response of crops under different SSTs was significantly positively correlated with FGP and the average grain weight of the seeds. Two SSTs (CK and LC3) were performed in 2018 (EXP2), which confirmed that the yield response of LC3 crops (25.1%) to eCO2 was significantly higher than that of CK (15.9%). Among the different grain positions, yield response to eCO2 of grains attached to the lower secondary rachis was greater than that of grains attached to the upper primary rachis. Reducing the source-sink ratio via leaf-cutting enhanced the net photosynthetic rate response of the remaining leaves to eCO2 and increased the grain filling ability. Conversely, spikelet removal increased the non-structural carbohydrate (NSC) content of the stem, causing feedback inhibition and photosynthetic down-regulation. This study suggests that reducing the source-sink ratio by adopting appropriate management measures can increase the response of rice to eCO2.

Allowing the Load to Swing Reduces the Mechanical Energy of the Stance Leg and Improves the Lateral Stability of Human Walking.

Loaded walking with typical rigid backpack results in a significant increase in the mechanical energy of the stance leg and a decrease in lateral stability. Allowing the load to swing, which has been applied in shoulder pole, a tool widely used in Asia for load carriage assistance, may attenuate these effects. This paper theoretically analyzes and experimentally validates the biomechanical and energetic effects of the swinging loads. When walking with a 30 kg load, allowing the load to swing reduces the fore-aft leg impulses by over 19% and further reduces the mechanical energy of the stance leg by 12.9% compared to the typical rigid backpack. The whole-body metabolic cost has no significant change, which may be attributed to the increase in the muscle work of the upper body and the leg swing. Moreover, the load movement out of phase to the human in the lateral direction reduces the lateral excursion of extrapolated center-of-mass by 27.2%, indicating an increase in the lateral margin of stability and implying an improvement in lateral stability. The results demonstrate that allowing the load to swing reduces the horizontal leg impulses and the mechanical energy of the stance leg, and improves the lateral stability of human walking.

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.

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.

Ozone-induced reduction in rice yield is closely related to the response of spikelet density under ozone stress.

Six modern rice cultivars, including three indica and three japonica cultivars were exposed to 100 ppb ozone (8 h per day) and control conditions throughout cropping season in 2016 to 2017 at Yangzhou, China. Ozone decreased plant height and inhibited tillering development as well as panicle number per plant of all cultivars, but had no effect on the productive tiller ratio. Ozone significantly decreased spikelet number per panicle, spikelet number per plant, fully-filled grain percentage and fully-filled grain weight, resulting in yield decrease by 39.3% on average for all cultivars and by 42.6 and 34.4% in the indica and the japonica groups, respectively. The response of aboveground biomass to ozone was similar to that of yield, albeit with a lower decrease, which led to a 7.6% decrease in harvest index. In terms of grain positions (grains attached to the upper primary rachis: superior spikelet (SS); grains attached to the lower secondary rachis: inferior spikelet (IS), and the remaining grains: medium spikelet (MS)), the ozone-induced change in yield traits (yield, spikelet number per panicle, spikelet number per plant, fully-filled grain percentage, and empty grain percentage) followed the order IS > MS > SS, as indicated by the significant interaction between ozone and grain position. Although ozone had negative effects on all yield traits, only ozone-induced reduction in spikelet density (spikelet number per panicle and or spikelet number per plant) was significantly correlated to yield loss. Grain yield showed significant ozone by cultivar and ozone by year interactions, indicating ozone impacts on rice yield varied with meteorological conditions and cultivars.

[Effects of elevated CO2 concentration on grain filling capacity and quality of rice grains located at different positions on a panicle.] / 高浓度CO2对稻穗不同位置籽粒结实和米质性状的影响.

The rising atmospheric CO2 concentration affects spikelets development, grain filling process, and rice quality. However, it is unclear that whether such effects are related to grain positions on rice panicle. By using a rice FACE (Free-Air CO2 Enrichment) platform, we grew a japoni-ca rice cultivar Wuyunjing 23, characterized with high yield and good quality, under ambient (Ambient) and elevated CO2 concentrations (+200 µmol·mol-1, FACE). The effects of increased CO2 concentration on spikelet density, grain filling capacity, the appearance and eating quality of rice grains were examined and the association of such effects with grain positions on rice panicle were investigated. The results showed that CO2 enrichment increased grain yield of Wuyunjing 23 by 18.3%. The panicle number per unit land area and filled-grain weight increased by 21.4% and 9.4%, respectively; whereas the number of spikelets per panicle and filled-grain percentage decreased by 9.0% and 2.2%, respectively. The decreased filled-grain percentage of rice grown under FACE treatment was mainly related to the increases of empty-grain percentage in all parts of rice panicle. The decrease of rice spikelets number per panicle by FACE treatment was mainly due to the substantial decrease of surviving spikelets of secondary branches in upper and middle parts of rice panicles instead of other positions. The CO2-induced changes of filled-grain weight and filled-grain percentage were similar among grains located at different positions on rice panicle. FACE treatment reduced the green grain rate and increased the grain length and width, with the grains at different positions on rice papnicle showing similar responses. FACE significantly increased chalky grain percentage by 59% and chalkiness degree by 55%, with the increases for both parameters following the order of primary branches＞secondary branches and upper part＞middle part＞lower part. FACE treatment slightly increased amylose content while decreased peak viscosity, hot viscosity, breakdown, final viscosity and setback, but most of these effects were nonsignificant. The gelatinization temperature of rice also reduced by 5% under FACE, and the decrease of inferior spikelets was greater than that of superior spikelets. In summary, the yield increase of Wuyunjing 23 under high CO2 concentration was mainly related to the increases of panicle number and individual grain weight, while the panicle size was reduced. Elevated CO2 concentration reduced green grain percentage but increased grain chalkiness, and had little effect on cooking and eating quality. The grain positions on rice panicle affected the responses of spikelets development, grain filling capacity and grain quality of rice to elevated CO2 concentration, but the effects varied across different indices.

[Effects of ozone stress on amylose content and starch RVA profile in grains located at diffe-rent positions on a panicle]. / 臭氧胁迫对稻穗不同部位糙米直链淀粉含量和RVA谱特征值的影响.

The increase of ground-level ozone concentration significantly reduces rice yield, but its effect on grain quality in association with the positions on a panicle was largely unknown. The effects of ozone stress on amylose content and RVA profile of rice grains located at different positions of panicles were studied by using a sunlit gas fumigation platform. Eight varieties representing different types of rice were fumigated under ambient (9 nL·L-1) or elevated ozone (100 nL·L-1) concentrations from transplanting until maturity. The results showed that elevated ozone treatment significantly reduced amylose content, maximum viscosity, hot viscosity, breakdown and cold viscosity by 5.9%, 7.6%, 5.9%, 11.6%, 2.9%, respectively, but increased the setback and gelatinization temperature by 24.9% and 1.0%. There were significant differences among varieties for amylose content and all parameters in RVA profile. The grains located at different positions on a panicle differed in amylose content, maximum viscosity, hot viscosity, breakdown and cold viscosity. The superior grains located at the upper part of a panicle had the highest value and the inferior grains located at the lower part of a panicle had the lowest value. However, the setback in RVA profile showed a different trend, with the superior grains having the lowest setback but inferior grains having the highest setback. In most cases, there were significant interactive effects of ozone by year or ozone by variety on amylose content and RVA profile. No significant ozone by grain position interaction on RVA profile was found, although the responses of superior grains to ozone stress was slightly smaller than those of inferior grains or grains located at the middle part of a panicle. The results demonstrated that ozone fumigation of 100 nL·L-1 during rice growing season deteriorated rice quality, with the magnitude of deterioration varying with growth seasons and varieties and little impacts of grain positions on a panicle.

Causes of variation among rice models in yield response to CO2 examined with Free-Air CO2 Enrichment and growth chamber experiments.

The CO2 fertilization effect is a major source of uncertainty in crop models for future yield forecasts, but coordinated efforts to determine the mechanisms of this uncertainty have been lacking. Here, we studied causes of uncertainty among 16 crop models in predicting rice yield in response to elevated [CO2] (E-[CO2]) by comparison to free-air CO2 enrichment (FACE) and chamber experiments. The model ensemble reproduced the experimental results well. However, yield prediction in response to E-[CO2] varied significantly among the rice models. The variation was not random: models that overestimated at one experiment simulated greater yield enhancements at the others. The variation was not associated with model structure or magnitude of photosynthetic response to E-[CO2] but was significantly associated with the predictions of leaf area. This suggests that modelled secondary effects of E-[CO2] on morphological development, primarily leaf area, are the sources of model uncertainty. Rice morphological development is conservative to carbon acquisition. Uncertainty will be reduced by incorporating this conservative nature of the morphological response to E-[CO2] into the models. Nitrogen levels, particularly under limited situations, make the prediction more uncertain. Improving models to account for [CO2] × N interactions is necessary to better evaluate management practices under climate change.

Physiological and genotype-specific factors associated with grain quality changes in rice exposed to high ozone.

Rising tropospheric ozone concentrations in Asia affect the yield and quality of rice. This study investigated ozone-induced changes in rice grain quality in contrasting rice genotypes, and explored the associated physiological processes during the reproductive growth phase. The ozone sensitive variety Nipponbare and a breeding line (L81) containing two tolerance QTLs in Nipponbare background were exposed to 100 ppb ozone (8 h per day) or control conditions throughout their growth. Ozone affected grain chalkiness and protein concentration and composition. The percentage of chalky grains was significantly increased in Nipponbare but not in L81. Physiological measurements suggested that grain chalkiness was associated with a drop in foliar carbohydrate and nitrogen levels during grain filling, which was less pronounced in the tolerant L81. Grain total protein concentration was significantly increased in the ozone treatment, although the albumin fraction (water soluble protein) decreased. The increase in protein was more pronounced in L81, due to increases in the glutelin fraction in this genotype. Amino acids responded differently to the ozone treatment. Three essential amino acids (leucine, methionine and threonine) showed significant increases, while seven showed significant treatment by genotype interactions, mostly due to more positive responses in L81. The trend of increased grain protein was in contrast to foliar nitrogen levels, which were negatively affected by ozone. A negative correlation between grain protein and foliar nitrogen in ozone stress indicated that higher grain protein cannot be explained by a concentration effect in all tissues due to lower biomass production. Rather, ozone exposure affected the nitrogen distribution, as indicated by altered foliar activity of the enzymes involved in nitrogen metabolism, such as glutamine synthetase and glutamine-2-oxoglutarate aminotransferase. Our results demonstrate differential responses of grain quality to ozone due to the presence of tolerance QTL, and partly explain the underlying physiological processes.

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

BACKGROUND: Rising atmospheric CO2 is accompanied by global warming. However, interactive effects of elevated CO2 and temperature have not been well studied on grain quality of rice. A japonica cultivar was grown in the field using a free-air CO2 enrichment facility in combination with a canopy air temperature increase system in 2014. The gas fumigation (200 µmol mol(-1) above ambient CO2 ) and temperature increase (1 °C above ambient air temperature) were performed from tillering until maturity. RESULTS: Compared with the control (ambient CO2 and air temperature), elevated CO2 increased grain length and width as well as grain chalkiness but decreased protein concentrations. In contrast, the increase in canopy air temperature had less effect on these parameters except for grain chalkiness. The starch pasting properties of rice flour and taste analysis of cooked rice indicated that the palatability of rice was improved by CO2 and/or temperature elevation, with the combination of the two treatments showing the most significant changes compared with ambient rice. CONCLUSION: It is concluded that projected CO2 in 2050 may have larger effects on rice grain quality than the projected temperature increase. Although deterioration in milling suitability, grain appearance and nutritional quality can be expected, the taste of cooked rice might be better in the future environment. © 2015 Society of Chemical Industry.

[Effects of ozone stress on photosynthesis and dry matter production of rice II -you 084 under different Planting densities].

In order to investigate the effects of ozone stress on photosynthesis, dry matter production, non-structural carbohydrate and yield formation of rice, a free air ozone concentration enrichment (FACE) experiment was conducted. A super hybrid rice cultivar II-you 084 with 3 spacing levels, low plant density (LD, 16 hills per m2), medium (MD, 24 hills per m2) and high plant density (HD, 32 hills per m2), was grown in the field at current and elevated ozone concentrations (current × 1.5). The results were as follows: Elevated ozone significantly reduced leaf SPAD value of UI-you 084 by 6%, 11% and 13%, at 63, 77, and 86 days after transplanting, respectively. The declines in leaf net photosynthetic rate, stomatal conductance and transpiration rate at filling stage increased significantly on ozone stress over time. Ozone stress decreased dry matter production of rice by 46% from heading stage to plant maturity, thus reduced biomass yield by 25%. Elevated ozone decreased the concentration and accumulation of soluble carbohydrate and starch in stem of II-you 084 at jointing, heading and plant maturity, but significantly increased the dry matter transportation rate. No significant interaction was observed between ozone and planting density for photosynthesis, dry matter production and non-structural carbohydrate of rice. The above results indicated that elevated ozone reduced photosynthesis and growth of rice II-you 084 at late growth stage, which had no relationship with planting density.

Elevated tropospheric ozone increased grain protein and amino acid content of a hybrid rice without manipulation by planting density.

BACKGROUND: Rising tropospheric ozone affects crop yield and quality. Rice protein concentration, which is closely associated with eating/cooking quality, is of critical importance to nutritional quality. The ozone effect on amino acids of rice grains was little known, especially grown under different cultivation conditions. A hybrid rice cultivar Shanyou 63 was grown in 2010 and 2011 to investigate the interactive effect of ozone exposure and planting density on rice protein quality in a free-air ozone enrichment system. RESULTS: The content of protein, total amino acids (TAA), total essential (TEAA) and non-essential amino acids (TNEAA) in rice grain was increased by 12-14% with elevated ozone. A similar significant response to ozone was observed for concentrations of the seven essential and eight non-essential amino acids. In contrast, elevated ozone caused a small but significant decrease in percentage of TEAA to TAA. The year effect was significant for all measured traits; however, interactions of ozone with year or planting density were not detected. CONCLUSION: The study suggested that season-long elevation of ozone concentration to projected 2050 levels will increase protein and amino acids of Shanyou 63, and crop management such as changing planting density might not alter the impact.

Effects of elevated ozone, carbon dioxide, and the combination of both on the grain quality of Chinese hybrid rice.

The effects of CO2 and/or O3 elevation on rice grain quality were investigated in chamber experiments with gas fumigation performed from transplanting until maturity in 2011 and 2012. Compared with the control (current CO2 and O3 concentration), elevated CO2 caused a tendency of an increase in grain chalkiness and a decrease in mineral nutrient concentrations. In contrast, elevated O3 significantly increased grain chalkiness and the concentrations of essential nutrients, while changes in starch pasting properties indicated a trend of deterioration in the cooking and eating quality. In the combination of elevated CO2 and O3 treatment, only chalkiness degree was significantly affected. It is concluded that the O3 concentration projected for the coming few decades will have more substantial effects on grain quality of Chinese hybrid rice than the projected high CO2 concentration alone, and the combination of two gases caused fewer significant changes in grain quality than individual gas treatments.

[Effects of increasing surface ozone concentration on spikelet formation of hybrid rice cultivars].

To investigate the effects of high ozone concentration on spikelet formation of hybrid rice cultivars, an experiment using a unique free air ozone concentration enrichment (ozone-FACE) system was conducted in 2007. Two hybrid rice cultivars, Shanyou 63 (SY63) and Liangyoupeijiu (LYPJ), were grown at ambient and elevated (target at 50% above ambient) ozone concentration. The results showed that compared with ambient ozone concentration, elevated ozone reduced the spikelet number per panicle by 28 and 34 (relative decrease of 15% and 13%) for SY63 and LYPJ, respectively. This reduction in spikelet number per panicle was mainly contributed to the significant decrease in spikelet number on secondary branches (SB), while only minor response was detected for the spikelet number on primary branches (PB), resulting in an increase in percentage of primary branch spikelets and a decrease in percentage of secondary branch spikelets under ozone exposure. In terms of spikelet formation, the large ozone-induced reduction in spikelet number per panicle of the two hybrid cultivars was entirely due to the suppression of spikelet differentiation per panicle (especially that on SB), while the degenerated spikelets per panicle decreased rather than increased under ozone exposure. It was suggested that corresponding measures should be adopted to mitigate the detrimental effects of ozone on the spikelet differentiation to minimize yield loss under increasing surface ozone concentration.

[Responses of rice growth and development to elevated near-surface layer ozone (O3) concentration: a review].

Ozone (O3) is recognized as one of the most important air pollutants. At present, the worldwide average tropospheric O3 concentration has been increased from an estimated pre-industrial level of 38 nl L(-1) (25-45 nl L(-1), 8-h summer seasonal average) to approximately 50 nl L(-1) in 2000, and to 80 nl L(-1) by 2100 based on most pessimistic projections. Oryza sativa L. (rice) is the most important grain crop in the world, and thus, to correctly evaluate how the elevated near-surface layer O3 concentration will affect the growth and development of rice is of great significance. This paper reviewed the chamber (including closed and open top chamber)-based studies about the effects of atmospheric ozone enrichment on the rice visible injury symptoms, photosynthesis, water relationship, phenology, dry matter production and allocation, leaf membrane protective system, and grain yield and its components. Further research directions in this field were discussed.

[Effects of free-air CO2 enrichment on nitrogen uptake and utilization of wheat].

In this paper, the effects of free-air CO2 enrichment (FACE) and its interaction with nitrogen supply on the nitrogen content, uptake, allocation, and use efficiency of winter wheat variety Ningmai 9 at its different growth stages were studied in 2001-2003. The results showed that under FACE treatment, the nitrogen content in wheat plant sampled at different growth stages all decreased significantly, with an average decrement of 4.4% to 13.4% compared with the control. The nitrogen accumulation under FACE increased significantly (9.2% -32.3%), and the increasing rate was larger at middle growth stage than at early and late growth stages. Nitrogen fraction was higher in stem, but lower in leaf. As for spike, the accumulation of nitrogen depended on the growth stage. FACE resulted in a significant increase (5.5% -10.3%) of nitrogen use efficiency for biomass production at all growth stages, of nitrogen harvest index (16.3%) at maturing stage, and of nitrogen use efficiency (9.3%) for grain yield. Nitrogen application increased the nitrogen content of wheat plant and its N uptake at all growth stages, decreased the nitrogen use efficiency, but had less effect on the nitrogen allocation in different organs.

[Effects of free-air CO2 enrichment (FACE) on dry matter production and allocation in wheat].

A free-air CO2 enrichment (FACE) experiment was conducted in 2001-2003 to study the effects of predicted higher CO2 levels on the dry matter (DM) production and allocation in winter wheat variety Ningmai 9. The results showed that under FACE, the DM production had an increase of 10. 8% , 31. 6% , 40. 5% and 27. 2% during the growth periods from sowing to wintering ( Period 1 ) , wintering to jointing ( Period 2) , jointing to booting ( Period 3) , and booting to heading (Period 4) , respectively, but a decrease of 5. 5% in the period from heading to grain maturity (Period 5). As a result, the final total biomass at maturity was increased by 13. 6%. FACE had no significant effect on leaf area index (LAI) and net assimilation rate (NAR) in Period 1, but made the LAI in Period 2 increased obviously, and the NAR decreased dramatically in Period 3. Under FACE, the proportion of leaf to total above-ground DM decreased, while that of stem (including sheath) to total above-ground DM showed an opposite trend in the whole growth period. The percentage and total amount of soluble sugar and starch in the stem at grain-filling stage were also increased obviously under FACE.