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We investigated temporal changes in paddy rice phenology and yield under climatic and varietal changes in Shonai region, Yamagata Prefecture, northeast Japan across a period of 1982–2017. In the study region, the dominant variety shifted from Sasanishiki to Haenuki in mid 1990s. Temporal trends across the study period were significant in mean air temperatures for the months from May to July, and the temperature rise has accelerated heading, which was delayed by the varietal shift. We built models of the effects of climatic and varietal changes on phenological events and yield components: number of grains per land area, percentage ripened grains, and 1000-grain weight. Combining the yield component models, we built a yield model, with which we estimated the effect of the temperature rise from May to July on the yield. The temperature rise in May and June has reduced the yield by accelerating phenology, while that in July has increased the yield by raising 1000-grain weight. The net effect was no change in the yield across the study period, which, however, does not indicate an insensitivity of the yield to the temperature rise. Rather, the finding points to the dependency of the net change in the yield on seasonal pattern of the climate change. Climate change impacts on rice should therefore be quantified on the changes at monthly or shorter time scale rather than a seasonal mean. Our finding also points to the need to pay attention to the changes in agronomic practices such as varieties. [ABSTRACT FROM AUTHOR]

Increased concentrations of atmospheric CO2 are predicted to reduce the content of essential elements such as protein, zinc, and iron in C3 grains and legumes, threatening the nutrition of billions of people in the next 50 years. However, this prediction has mostly been limited to grain crops, and moreover, we have little information about either the underlying mechanism or an effective intervention to mitigate these reductions. Here, we present a broader picture of the reductions in elemental content among crops grown under elevated CO2 concentration. By using a new approach, flow analysis of elements, we show that lower absorption and/or translocation to grains is a key factor underlying such elemental changes. On the basis of these findings, we propose two effective interventions—namely, growing C4 instead of C3 crops, and genetic improvements—to minimize the elemental changes in crops, and thereby avoid an impairment of human nutrition under conditions of elevated CO2. [ABSTRACT FROM AUTHOR]

Abstract: Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean > wheat > maize > rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010–2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the “ozone yield gaps”), adding up to 227 Tg of lost yield. Our modelling shows that the highest ozone‐induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution‐focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap. [ABSTRACT FROM AUTHOR]

Organic farming aims to reduce the effect on the ecosystem and enhance biodiversity in agricultural areas, but the long-term effectiveness of its application is unclear. Assessments have rarely included various taxonomic groups with different ecological and economic roles. In paddy fields with different numbers of years elapsed since the transition from conventional to organic farming, we investigated changes in the abundance of insect pests, generalist predators, and species of conservation concern. The abundance of various arthropods exhibited diverse trends with respect to years elapsed since the transition to organic farming. Larval lepidopterans, Tetragnatha spiders, and some planthoppers and stink bugs showed non-linear increases over time, eventually reaching saturation, such as the abundance increasing for several years and then becoming stable after 10 years. This pattern can be explained by the effects of residual pesticides, the lag time of soil mineralization, and dispersal limitation. A damselfly (Ischnura asiatica) did not show a particular trend over time, probably due to its rapid immigration from source habitats. Unexpectedly, both planthoppers and some leafhoppers exhibited gradual decreases over time. As their abundances were negatively related to the abundance of Tetragnatha spiders, increased predation by natural enemies might gradually decrease these insect populations. These results suggest that the consideration of time-dependent responses of organisms is essential for the evaluation of the costs and benefits of organic farming, and such evaluations could provide a basis for guidelines regarding the length of time for organic farming to restore biodiversity or the economic subsidy needed to compensate for pest damage. [ABSTRACT FROM AUTHOR]

Rising atmospheric CO2 concentrations will probably increase rice (Oryza sativa L.) yield but decrease grain nitrogen (GN) concentration. Grains attached to different positions in the panicles differ greatly in weight and quality, but their responses to elevated CO2 (e[CO2]) are poorly understood, which limits our understanding of the mechanisms of yield enhancement and quality degradation. Thus a free-air CO2 enrichment experiment was conducted to examine the effects of e[CO2] on grain mass (GM), grain carbon (GC), and GN accumulation in the spikelets attached to the upper primary rachis branch (superior spikelets; SS) and those attached to the lower secondary rachis (inferior spikelets; IS). e[CO2] stimulated the rice yield by 13% but decreased the N concentration in the panicle by 7% when averaged over two levels of N fertilizations (P < 0.01). The responses of SS and IS to e[CO2] were different particularly under higher N supply. For SS, e[CO2] decreased GN by 24% (P < 0.01) but did not affect GM. For IS, e[CO2] increased GM by 13% (P < 0.05) but GN was not affected. The reduction of GN due to e[CO2] started to appear at the beginning of grain filling. These results suggest that future [CO2] levels probably stimulate the grain growth of IS, most of which are not marketable due to limited size, at the expense of GN reduction in SS. Translocation of N from SS to IS may be a possible mechanism for reduction in GN of SS. This may degrade the grain quality of marketable rice under e[CO2]. [ABSTRACT FROM AUTHOR]

Physiological and biochemical studies on the leaf apoplast have been facilitated by the use of the infiltration–centrifugation technique to collect intercellular washing fluid (IWF). However, this technique has been difficult to implement in rice (Oryza sativa L.) for various reasons. We compared the collection efficiency of leaf IWF between two types of rice varieties (Indica and Japonica), as well as between rice and other species (spinach, snap bean and wheat). Although the extraction of IWF in most species took only 2–3 min, it took up to 35 min in rice. The difficulty in infiltration with rice was ascribed to the small stomatal aperture and hydrophobicity of the leaves. In this study, we have established an improved method for collecting IWF and determining the apoplastic air and water volumes in rice leaves. We have shortened the infiltration time to 8 min via the following improvements: (i) infiltration under outdoor shade in the daytime to prevent stomatal closure and a rise in temperature of the infiltration medium; (ii) soaking of leaves in a surfactant solution to decrease the leaf hydrophobicity; and (iii) continuous pressurization using a sealant injector to facilitate the infiltration. The rapid collection of IWF achieved using this technique will facilitate study of the leaf apoplast in rice. [ABSTRACT FROM AUTHOR]

Understanding of leaf stomatal responses to the atmospheric CO2 concentration, [CO2], is essential for accurate prediction of plant water use under future climates. However, limited information is available for the diurnal and seasonal changes in stomatal conductance ( gs) under elevated [CO2]. We examined the factors responsible for variations in gs under elevated [CO2] with three rice cultivars grown in an open-field environment under flooded conditions during two growing seasons (a total of 2140 individual measurements). Conductance of all cultivars was generally higher in the morning and around noon than in the afternoon, and elevated [CO2] decreased gs by up to 64% over the 2 years (significantly on 26 out of 38 measurement days), with a mean gs decrease of 23%. We plotted the gs variations against three parameters from the Ball-Berry model and two revised versions of the model, and all parameters explained the gs variations well at each [CO2] in the morning and around noon ( R2 > 0.68), but could not explain these variations in the afternoon ( R2 < 0.33). The present results provide an important basis for modelling future water use in rice production. [ABSTRACT FROM AUTHOR]

The effects of elevated O3 concentration ([O3]) on grain yield and photosynthetic characteristics of flag leaves in rice (Oryza sativa L.) were studied using a hybrid indica cultivar SY63 and a conventional Japonica cultivar WYJ3. Both cultivars were grown in the field under ambient (A-O3) and elevated [O3] (E-O3, ambient×1.5) using free-air O3 enrichment in Jiangdu city, Jiangsu province, China. The E-O3 significantly reduced above-ground biomass (p =0.047) and grain yield (p =0.0046), but had no significant effect on harvest index (p =0.18) across cultivars. The hybrid Indica cultivar SY63 was more sensitive to E-O3 than the conventional Japonica cultivar WYJ3. The above-ground biomass was reduced by 17.6% for SY63 and 6.6% for WYJ3, whereas the grain yield was reduced by 20.7% for SY63 and 6.3% for WYJ3. A barely non-significant (p =0.079) interaction between O3 and cultivar on grain yield suggested a higher sensitivity of the hybrid variety: SY63. In SY63, flag leaves exhibited an earlier and stronger response in photosynthetic characteristics to E-O3. Depression in light-saturated photosynthetic rate (A sat) was first observed at 237 day of year (DOY) in SY63, and the seasonal mean A sat was reduced by 23.1%. In contrast, for WYJ3, the conventional cultivar, the impact of E-O3 on A sat was negligible until 266 DOY, and seasonal mean decrease of A sat was only 9.4%. The same trend was found in chlorophyll a fluorescence parameters. In SY63, actual quantum yield of PSII (p =0.007) and q p (photochemical quenching) (p =0.002) were significantly decreased at 248 DOY and the downward trends persisted throughout the rest of the life span of flag leaves. No such changes were observed in WYJ3. In the ozonated flag leaves of SY63, necrotic damages occurred and chlorophyll contents declined significantly by 12.6¿43.6% through the entire functional duration of the leaf. As for WYJ3, chlorophyll remained unaffected until a 25.7% decrease appeared at 278 DOY under E-O3. The observed yield losses were compared with those estimated from two existing exposure¿yield loss relationships for rice. The yield loss in SY63 was much greater than either estimate, whereas that in WYJ3 was comparable to one estimate but was moderately larger than the other. This warrants further studies with a much larger number of varieties. Open-air O3 release would serve as the best platform for such a large-scale screening of rice varieties to increasing [O3]. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Meta-analysis was conducted to quantitatively assess the effects of rising ozone concentrations ([O3]) on yield and yield components of major food crops: potato, barley, wheat, rice, bean and soybean in 406 experimental observations. Yield loss of the crops under current and future [O3] was expressed relative to the yield under base [O3] (≤26ppb). With potato, current [O3] (31–50ppb) reduced the yield by 5.3%, and it reduced the yield of barley, wheat and rice by 8.9%, 9.7% and 17.5%, respectively. In bean and soybean, the yield losses were 19.0% and 7.7%, respectively. Compared with yield loss at current [O3], future [O3] (51–75ppb) drove a further 10% loss in yield of soybean, wheat and rice, and 20% loss in bean. Mass of individual grain, seed, or tuber was often the major cause of the yield loss at current and future [O3], whereas other yield components also contributed to the yield loss in some cases. No significant difference was found between the responses in crops grown in pots and those in the ground for any yield parameters. The ameliorating effect of elevated [CO2] was significant in the yields of wheat and potato, and the individual grain weight in wheat exposed to future [O3]. These findings confirm the rising [O3] as a threat to food security for the growing global population in this century. [Copyright &y& Elsevier]

Maturity group (based on the number of days to maturity) is an important growth trait for determining crop productivity, but there has been no attempt to examine the effects of elevated [CO2] on yield enhancement of rice cultivars with different maturity groups. Since early-maturing cultivars generally show higher plant N concentration than late-maturing cultivars, it is hypothesized that [CO2]-induced yield enhancement might be larger for early-maturing cultivars than late-maturing cultivars. To test this hypothesis, the effects of elevated [CO2] on yield components, biomass, N uptake, and leaf photosynthesis of cultivars with different maturity groups were examined for 2 years using a free-air CO2 enrichment (FACE). Elevated [CO2] significantly increased grain yield and the magnitude significantly differed among the cultivars as detected by a significant [CO2]×cultivar interaction. Two cultivars (one with early and one with late maturity) responded more strongly to elevated [CO2] than those with intermediate maturity, resulting mainly from increases in spikelet density. Biomass and N uptake at the heading stage were closely correlated with grain yield and spikelet density over [CO2] and cultivars. Our 2 year field trial rejected the hypothesis that earlier cultivars would respond more to elevated [CO2] than later cultivars, but it is revealed that the magnitude of the growth enhancement before heading is a useful criterion for selecting rice cultivars capable of adapting to elevated [CO2]. [ABSTRACT FROM PUBLISHER]

A 13C pulse-labeling experiment was conducted under ambient CO2 and free-air CO2 enrichment (FACE) conditions to understand how elevated CO2 affects the CH4 in soil bubbles and CH4 emissions from rice paddies. Two hills of rice plants enclosed by frames in ambient CO2 and FACE plots were labeled with 13CO2 at the panicle formation stage, and plants and soil bubbles were collected 2 and 51 days after the pulse labeling. CH4 and 13CH4 emissions were also measured by the closed-chamber method between the 2 bubble samplings. Conversion of photosynthate carbon to CH4 entrapped in soil bubbles and CH4 emission to the atmosphere occurred quickly, suggesting that recent photosynthates can be an important source of carbon for methanogenesis. About 1% of the 13C-labeled C taken up through photosynthesis was emitted as 13CH4 during the 7 weeks of measurement, most during the first 3 weeks after labeling. Total CH4 and 13CH4 emissions did not differ between the ambient CO2 and FACE treatments, because the entrapped CH4 in the soil and the root biomass were not affected by elevated CO2 levels in this study. [ABSTRACT FROM AUTHOR]

A comprehensive biogeochemistry model, DNDC, was revised to simulate crop growth and soil processes more explicitly and improve its ability to estimate methane (CH4) emission from rice paddy fields under a wide range of climatic and agronomic conditions. The revised model simulates rice growth by tracking photosynthesis, respiration, C allocation, tillering, and release of organic C and O2 from roots. For anaerobic soil processes, it quantifies the production of electron donors [H2 and dissolved organic carbon (DOC)] by decomposition and rice root exudation, and simulates CH4 production and other reductive reactions based on the availability of electron donors and acceptors (NO3−, Mn4+, Fe3+, and SO42−). Methane emission through rice is simulated by a diffusion routine based on the conductance of tillers and the CH4 concentration in soil water. The revised DNDC was tested against observations at three rice paddy sites in Japan and China with varying rice residue management and fertilization, and produced estimates consistent with observations for the variation in CH4 emission as a function of residue management. It also successfully predicted the negative effect of (NH4)2SO4 on CH4 emission, which the current model missed. Predicted CH4 emission was highly sensitive to the content of reducible soil Fe3+, which is the dominant electron acceptor in anaerobic soils. The revised DNDC generally gave acceptable predictions of seasonal CH4 emission, but not of daily CH4 fluxes, suggesting the model's immaturity in describing soil heterogeneity or rice cultivar-specific characteristics of CH4 transport. It also overestimated CH4 emission at one site in a year with low temperatures, suggesting uncertainty in root biomass estimates due to the model's failure to consider the temperature dependence of leaf area development. Nevertheless, the revised DNDC explicitly reflects the effects of soil electron donors and acceptors, and can be used to quantitatively estimate CH4 emissions from rice fields under a range of conditions. [ABSTRACT FROM AUTHOR]

The projected increase of atmospheric CO2 concentration ([CO2]) is expected to increase rice yield, but little is known of the effects of [CO2] at low temperature, which is the major constraint to growing rice in cool climates. We grew rice under two levels of [CO2] (ambient and elevated by 200 μmol mol−1) and two nitrogen (N) fertilization regimes in northern Japan in 2003 (cool weather) and 2004 (warm weather) in the field in a free-air CO2 enrichment (FACE) system. Elevated [CO2] significantly increased grain yield in both years in both N regimes, but the magnitude of the increase differed between years: 6% in 2003 vs. 17% in 2004, with a significant interaction between [CO2] and year. This difference resulted from responses of spikelet number and ripening percentage to elevated [CO2]. Enhancement of dry matter production and N uptake at heading by elevated [CO2] was smaller in 2003 than in 2004, although at maturity there was no difference between years. No significant interaction between N regime and [CO2] was detected in yield and yield components. The results suggest that yield gain due to elevated [CO2] can be reduced by low temperature. [ABSTRACT FROM AUTHOR]

• Background and Aims Influences of rising global CO2 concentration and temperature on plant growth and ecosystem function have become major concerns, but how photosynthesis changes with CO2 and temperature in the field is poorly understood. Therefore, studies were made of the effect of elevated CO2 on temperature dependence of photosynthetic rates in rice (Oryza sativa) grown in a paddy field, in relation to seasons in two years.• Methods Photosynthetic rates were determined monthly for rice grown under free-air CO2 enrichment (FACE) compared to the normal atmosphere (570 vs 370 µmol mol−1). Temperature dependence of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vcmax) and the maximum rate of electron transport (Jmax) were analysed with the Arrhenius equation. The photosynthesis–temperature response was reconstructed to determine the optimal temperature (Topt) that maximizes the photosynthetic rate.• Key Results and Conclusions There was both an increase in the absolute value of the light-saturated photosynthetic rate at growth CO2 (Pgrowth) and an increase in Topt for Pgrowth caused by elevated CO2 in FACE conditions. Seasonal decrease in Pgrowth was associated with a decrease in nitrogen content per unit leaf area (Narea) and thus in the maximum rate of electron transport (Jmax) and the maximum rate of RuBP carboxylation (Vcmax). At ambient CO2, Topt increased with increasing growth temperature due mainly to increasing activation energy of Vcmax. At elevated CO2, Topt did not show a clear seasonal trend. Temperature dependence of photosynthesis was changed by seasonal climate and plant nitrogen status, which differed between ambient and elevated CO2. [ABSTRACT FROM AUTHOR]

The effects of elevated concentrations of atmospheric CO2 on CH4 and N2O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated CO2 significantly increased CH4 emission by 58% compared with ambient CO2. The CH4 emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated CO2 level, respectively. No CH4 was emitted from plant-free pots, suggesting that the main source of emitted CH4 was root exudates or autolysis products. Most N2O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO3 − contained in the experimental soil, and was not affected by the CO2 concentration. Pre-harvest drainage suppressed CH4 emission but did not cause much N2O emission (< 10 μg N m−2) from the rice-plant pots at both CO−1) from the rice-plant pots at both CO2 concentrations. [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]

Abstract: There have been several simulation studies of the effects of increasing CO2 concentration ([CO2]) on crop productivity, but confidence in these would be substantially enhanced if the models used in the studies are shown to mimic the effects of increasing [CO2] and interactions with other variables such as nitrogen and water supplies. Since rice is one of the major staple crops in the world, it is highly desirable to evaluate the climate change impacts on this crop. In this study, we tested Oryza2000 model against the observed growth and yield of rice plants in a 3-year field experiment, where rice plants were subjected to elevated [CO2] with free air carbon dioxide enrichment (FACE) under varying nitrogen (N) fertilization rates in farmers’ rice paddies in northern Japan. The simulation results showed that the model greatly overestimates the increase in peak green leaf area index due to elevated [CO2], but that it simulates the enhancement of total plant biomass with only a minor overestimation. The model was successful in simulating the increase in rice yield due to the CO2 enrichment, but it failed to reproduce the observed interaction with N in the rice yield response to elevated [CO2]. [Copyright &y& Elsevier]

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]

Methane (CH4) is a particularly potent greenhouse gas with a radiative forcing 23 times that of CO2 on a per mass basis. Flooded rice paddies are a major source of CH4 emissions to the Earth's atmosphere. A free-air CO2 enrichment (FACE) experiment was conducted to evaluate changes in crop productivity and the crop ecosystem under enriched CO2 conditions during three rice growth seasons from 1998 to 2000 in a rice paddy at Shizukuishi, Iwate, Japan. To understand the influence of elevated atmospheric CO2 concentrations on CH4 emission, we measured methane flux from FACE rice fields and rice fields with ambient levels of CO2 during the 1999 and 2000 growing seasons. Methane production and oxidation potentials of soil samples collected when the rice was at the tillering and flowering stages in 2000 were measured in the laboratory by the anaerobic incubation and alternative propylene substrates methods, respectively. The average tiller number and root dry biomass were clearly larger in the plots with elevated CO2 during all rice growth stages. No difference in methane oxidation potential between FACE and ambient treatments was found, but the methane production potential of soils during the flowering stage was significantly greater under FACE than under ambient conditions. When free-air CO2 was enriched to 550 ppmv, the CH4 emissions from the rice paddy field increased significantly, by 38% in 1999 and 51% in 2000. The increased CH4 emissions were attributed to accelerated CH4 production potential as a result of more root exudates and root autolysis products and to increased plant-mediated CH4 emissions because of the larger rice tiller numbers under FACE conditions. [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]

Summary • Season-long effects of elevated CO2 concentration ([CO2 ]) on the carbon balance of the rice (Oryza sativa ) canopy are reported here. • The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol-1 [CO2 ] (ambient) in three chambers, or at 650 µmol mol-1 (elevated) in the other three chambers. Canopy net photosynthesis and night-time respiration were determined in the chambers by mass balance. • Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the CO2 enrichment. But CO2 -induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated [CO2 ] was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew. • These results show that the increase in rice biomass by elevated [CO2 ] results more from the increase in carbon gain at early rather than later stages of growth. [ABSTRACT FROM AUTHOR]

Summary • Diurnal and seasonal changes in CO2 exchange between flooding water and the atmosphere are reported in a rice (Oryza sativa ) paddy field under ambient and free-air CO2 enrichment (FACE) conditions. • Measurements of CO2 exchange were made in a randomized complete-block design experiment with two CO2 mole fractions (ambient; FACE, ambient +200 mmol mol-1 ) and four blocks. • Evolution of CO2 from the flooding water occurred throughout the entire day under ambient CO2 , although the rate decreased in the daytime. By contrast, under FACE, CO2 evolution from the flooding water was observed at night, and CO2 absorption from the atmosphere was observed in the daytime. The time course of CO2 exchange was similar to that of solar radiation. • The diurnal pattern is similar to that for photosynthesis of terrestrial plant communities. This suggests that photosynthesis of the free-floating weeds and algae in the flooding water is related to the CO2 exchange between the flooding water and the atmosphere. In addition, the amplitude of the diurnal cycle of CO2 exchange was larger under the FACE than under ambient conditions. [ABSTRACT FROM AUTHOR]

Abstract: The publisher regrets that the following error has occurred in the above article: page 239, Table 1, and page 247, Table 5 should be replaced with below Tables in the original printing of the above-mentioned paper. [Copyright &y& Elsevier]

Abstract: Development of alternative soil fertility management is opted to mitigate the side effects associated with the excessive use of synthetic fertilizer. Soil fertility management practice through strengthening internal nutrient cycling (agroecological management: AEM) was examined in lowland rice (Oryza sativa) farming in Tochigi Prefecture, Japan. The principal study fields were established AEM (EAEM), where AEM was established in 1999 and transitional AEM (TAEM), where AEM has been practiced since 2009 and the field is still in transient stage. A field with conventional nutrient management (CNM) was studied for reference purposes. In EAEM field, potential amount of soil N supply was estimated at 41.9gNm−2 in spring 2011. Components in AEM maintained labile N pool were basic mineralizable N (21.0gNm−2) and annually changing mineralizable N (20.9gNm−2). Annually changing mineralizable N include soil drying effect (3.6gNm−2), internal inputs (13.2gNm−2) such as rice straw, rice bran, spring and winter weed as well as external inputs (4.1gNm−2) such as biological N2 fixation, precipitation and guano. Estimated NH4–N released from soil during the cropping season was 28.5gNm−2 in 2011. As the N uptake of rice was 11.5gNm−2 in 2011, EAEM supplied sufficient N to satisfy N demand by the rice plants. Relatively large amount of NH4–N released in EAEM implies that the recycling of on-site N sources would supply substantial amount of N to rice plants. In TAEM (two and three year practice), limited amount of NH4–N (17.8gNm−2) available during the cropping season compared with EAEM emphasized the importance of long-term practice to ensure effects of AEM through increase of basic soil mineralizable N. The research result suggests that AEM might be a sustainable and appropriate soil fertility management option for lowland rice farming if measures such as adjusting application rate of rice bran are employed to control soil N supply. [Copyright &y& Elsevier]

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]

Increasing atmospheric CO2 concentrations [CO2] are generally expected to enhance photosynthesis and growth of agricultural C3 cereal crops and as a result substantially increase yields. However, little is known about the combined effect of elevated [CO2] and nitrogen (N) supply on grain yield. To better understand the interactive effects of these factors on the yield of rice (Oryza sativa L.), we conducted a free-air CO2 enrichment (FACE) experiment at Shizukuishi, Iwate, Japan, in 1998–2000, using the japonica cultivar Akitakomachi. The target [CO2] of the elevated [CO2] plots was 200 ppmV above that in the ambient air. Three levels of N were supplied: low (LN, 4 g N m−2), medium (MN, 8 (1998) and 9 g N m−2 (1999, 2000)) and high N (HN, 12 (1998) and 15 g N m−2 (1999, 2000)). The MN level was similar to that recommended to local farmers. Across the 3 years, there was a positive [CO2]×N interaction for grain yield, with yields increasing only 7% with LN but about 15% with MN and HN. A similar interaction was found for fertile spikelet number per square meter. Across N levels and years, the [CO2]-induced increases in yield were closely related but less than the increases in total dry matter production: as a result harvest index (HI) decreased slightly with elevated [CO2]. This decrease in HI was due in part to a reduction in the number of productive (panicle bearing) tillers relative to total tiller number with elevated [CO2]. Yield increases were related most strongly to greater spikelet number per unit ground area, which in turn were due to increases in both panicle number per square meter and spikelet number per panicle. Small increases in individual grain mass with elevated [CO2] had only a minor effect on the overall yield increases. The spikelet number response to elevated [CO2] was limited with LN, but we found no evidence that N supply at levels greater than that recommended (i.e. above the MN level of N supply) resulted in further increases in spikelet number with elevated [CO2]. This suggests that for the cultivars and conditions of this experiment, the [CO2]-induced increases in yield will approach a ceiling at the recommended rates of N supply. [Copyright &y& Elsevier]

Summary • Season-long effects of elevated CO2 concentration ([CO2 ]) on the carbon balance of the rice (Oryza sativa ) canopy are reported here. • The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol-1 [CO2 ] (ambient) in three chambers, or at 650 µmol mol-1 (elevated) in the other three chambers. Canopy net photosynthesis and night-time respiration were determined in the chambers by mass balance. • Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the CO2 enrichment. But CO2 -induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated [CO2 ] was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew. • These results show that the increase in rice biomass by elevated [CO2 ] results more from the increase in carbon gain at early rather than later stages of growth. [ABSTRACT FROM AUTHOR]

Abstract Ozone is an important air pollutant that affects growth, transpiration, and water use efficiency (WUE) in plants. Integrated models of photosynthesis (A n) and stomatal conductance (G s) (A n - G s) are useful tools to consistently assess the impacts of ozone on plant growth, transpiration, and WUE. However, there is no information on how to incorporate the influence of ozone into A n - G s integrated models for crops. We focused on the Ball-Woodrow-Berry (BWB) relationship, which is a key equation in A n - G s integrated models, and aimed to address the following questions: (i) how does ozone change the BWB relationship for crops?; (ii) are there any difference in the changes in the BWB relationship among cultivars?, and (iii) how do the changes in the BWB relationship increase or decrease WUE for crops? We grew four rice cultivars in a field under ambient or Free-Air Concentration Enrichment (FACE) of ozone in China and measured A n and G s using a portable photosynthesis analyzer. We simulated WUE in individual leaves during the ripening period under different BWB relationships. The results showed that ozone significantly changed the BWB relationship only for the most sensitive cultivar, which showed an increase in the intercept of the BWB relationship under FACE conditions. These results imply that changes in the BWB relationship are related to the ozone sensitivity of the cultivar. Simulations of an A n - G s integrated model showed that increases in the intercept of the BWB relationship from 0.01 to 0.1 mol(H 2 O) m−2 s−1 indicated decreases in WUE by 22%. Since a reduction in WUE indicates increases in water demand per unit of crop growth, air pollution from ozone could be a critical issue in regions where agricultural water is limited, such as in rainfed paddy fields. Graphical abstract Unlabelled Image Highlights • Ozone significantly increased the intercept of the BWB relationship in rice. • This change was found for a rice cultivar with the highest sensitivity to ozone. • Increases in the intercept of the BWB relationship reflect a decreased water use efficiency. [ABSTRACT FROM AUTHOR]

Abstract: We parameterized a multiplicative model of stomatal conductance (g sto) for O3 uptake by rice leaves with the field measurements in a fully open-air ozone (O3) fumigation experiment. The estimated g sto compared well with the observed one (r 2 = 0.79). By using the g sto model for O3 uptake, we estimated a flux-based O3 risk (POD6, accumulated stomatal flux of O3 above a threshold of 6 nmol m−2 s−1) for rice across China in years 2000 and 2020, and compared it with the exposure-based O3 risk (AOT40, accumulated hourly O3 concentration above 40 ppb during daytime) for the same period. For the year 2000, both POD6 and AOT40 indicated the middle and lower reaches of Yangtze River and the south China being at the highest O3 risk. From the years 2000–2020, the O3 risks are projected to double (POD6) or triple (AOT40) in a majority of rice producing areas in the above two regions. Among three major rice cropping in the middle and lower reaches of Yangtze River, double-late rice is projected to have lower O3 risk than double-early rice and single rice on the either O3 risk measure in both 2000 and 2020. In south China, on the other hand, the O3 risks for double-late rice are comparable to that for early double-rice. In this study, the O3 risk was not measured as yield loss but as O3 flux and O3 exposure. The crop loss estimation would require a relationship between O3 flux and yield loss for major rice production regions across China. [Copyright &y& Elsevier]

Abstract: Tropospheric ozone is an air pollutant harmful to plants and animals. Its rapid increase at the ground surface has raised serious concern over damage to the quality and yield of agricultural crops. Reactive oxygen species (ROS) are formed in plant cells when that are exposed to a high concentration of ozone, and the ROS are thought to alter gene expression and result in cellular death. Clarification of the ROS formation will provide us with a better understanding of the physiological responses to and signaling pathways of ozone stress in plants. In this study, we investigated the mechanisms of the ROS formation in rice (Oryza sativa L.), the premier crop in Asia. To determine ROS distribution in rice leaves under acute ozone stress, we analyzed superoxide dismutase (SOD) expression, lipid peroxidation, NADPH oxidase activity, and in vivo H2O2 formation. Interestingly, chloroplastic, peroxisomal and mitochondrial SODs down-regulated their expression levels under ozone stress, whereas cytosolic SODs maintained their expression level. Higher lipid peroxidation occurred after the end of ozone exposure, which suggests lipid peroxidation may not be due to ozone directly, but rather to metabolic changes caused by the ozone exposure. Activity of NADPH oxidase did not show significant change. The in vivo analysis indicated accelerated formation of H2O2 about 24 h after the onset of exposure, which suggests that cellular death occurred around this time. [Copyright &y& Elsevier]

Abstract: For increasing rice production in West Africa, both expansion of rice harvested area and raising rice yield are required. Development of small-scale irrigation schemes is given high priority in national rice development plans. For realizing potential of the newly developed schemes, it is essential to understand yield level, farmers’ crop management practices and production constraints. A series of field surveys were conducted in six small-scale irrigation schemes in Zou department, Benin during the dry season in 2010–2011 to assess variation in rice yields and identify factors affecting the variation. The schemes were established between 1969 and 2009. Rice yields ranged from 1.3 to 7.8tha−1 with an average yield of 4.8tha−1. The average yield was only 2.9tha−1 for newer irrigation schemes developed in 2002 and 2009. Multiple regression analysis using farmers’ crop management practices as well as abiotic and biotic stresses as independent variables revealed that 75% of the variation in yields could be explained by five agronomic factors (fallow residue management, ploughing method, water stress, rat damage and N application rate) and two edaphic factors (sloped surfaces and sand content in the soil). Removing fallow residue from the fields for land preparation reduced yields. Yields were lower in plots ploughed by hand than by machine. Sloped surface, water stress and rat damage reduced yields. Yield increase due to N application ranged from 0.8 to 1.6tha−1. Higher sand content was associated with lowered yields. The low yields in new irrigation schemes caused by sub-optimal crop management practices suggest that farmer-to-farmer learning and extension of good agricultural principles and practices can increase yields. Organizational capacity is also important to ensure the use of common resources such as irrigation water and tractors for land preparation. [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]

Ozone is currently the most important air pollutant that negatively affects growth and yield of agricultural crops in most parts of the world, and rice is arguably the most important food crops on the planet. While a limited number of enclosure-based studies have examined the genotypic differences among rice (Oryza sativa L.) cultivars in response to increasing ozone concentration, no ozone experiment has been conducted to date under fully open-air field conditions to address this issue. In 2007, we conducted an experiment for the first time in the world with rice using free-air concentration enrichment (FACE) system at Xiaoji town, Jiangdu County, Jiangsu Province, China (119° 42′0″E, 32° 35′5″N). Four Chinese rice cultivars: Wujing 15 (WJ15, inbred japonica cultivar), Yangdao 6 (YD6, inbred indica cultivar), Shanyou 63 (SY63, three-line hybrid rice cultivar), Liangyoupeijiu (LYPJ, two-line hybrid rice cultivar), were grown at ambient or elevated (target at 50% above ambient) ozone concentration under nitrogen application rate of 15gNm−2. The ozone enhancement strongly accelerated phenologycal development of WJ15 and SY63, with maturity being reached by 4 and 8 days earlier, respectively, but only 1 day earlier for YD6 and LYPJ. Elevated ozone concentration reduced the number of mainstem leaves (ca. by half a leaf) and plant height at maturity (ca. by 3–5cm) of SY63 and LYPJ with no ozone effects detected in YD6 or WJ15. Among the cultivars tested, SY63 and LYPJ exhibited significant yield loss by exposure to ozone (−17.5%, −15%, respectively), while WJ15 and YD6 showed no responses. For all cultivars, no ozone effect was observed on panicle number per unit area as a result of no changes in both maximum tiller number or productive tiller ratio. However, the number of spikelets per panicle of SY63 and LYPJ showed a significant reduction due to ozone exposure, while those of WJ15 and YD6 remained unaffected. Meanwhile, ozone exposure also caused minor reductions in both filled spikelet percentage and individual grain mass. The results of this experiment indicated that yield loss due to ozone exposure differs among rice cultivars with hybrid cultivars (i.e., SY63 and LYPJ) exhibiting greater yield loss than inbred cultivars (i.e., WJ15 and YD6), which could be attributed to the suppression of spikelet formation in the hybrid cultivars under ozone stress. [Copyright &y& Elsevier]

Abstract: The projected increase of atmospheric CO2 concentration [CO2] is expected to increase yield of agricultural C3 crops, but little is known about effects of [CO2] on lodging that can reduce yield. This study examined the interaction between [CO2] and nitrogen (N) fertilization on the lodging of rice (Oryza sativa L.) using free-air CO2 enrichment (FACE) systems installed in paddy fields at Shizukuishi, Iwate, Japan (39°38′N, 140°57′E). Rice plants were grown under two levels of [CO2] (ambient=365μmolmol−1; elevated [CO2]=548μmolmol−1) and three N fertilization regimes: a single initial basal application of controlled-release urea (8gNm−2, CRN), split fertilization with a standard amount of ammonium sulfate (9gNm−2, MN), and ample N (15gNm−2, HN). Lodging score (six ranks at 18° intervals, with larger scores indicating greater bending), yield, and yield components were measured at maturity. The lodging score was significantly higher under HN than under CRN and MN, but lodging was alleviated by elevated [CO2] under HN. This alleviation was associated with the shortened and thickened lower internodes, but was not associated with a change in the plant''s mass moment around the culm base. A positively significant correlation between lodging score and ripening percentage indicated that ripening percentage decreased by 4.5% per one-unit increase in lodging score. These findings will be useful to develop functional algorithm that can be incorporated into mechanistic crop models to predict rice production more accurately in a changing climate and with different cultural practices. [Copyright &y& Elsevier]

Abstract: Controlled environment chambers were used to study the influence of elevated atmospheric CO2 concentration on CH4 and CO2 entrapped in soil bubbles and in solution in rice-paddy soil. Throughout the growing season, CO2 concentration was maintained at 383±11 μmol mol−1 during the day and 446±40 μmol mol−1 at night for ambient CO2 treatment, and at 706±13 μmol mol−1 (day) and 780±76 μmol mol−1 (night) for the elevated CO2 treatment. At the grain-filling stage of growth, rice plants in the chambers were supplied with 13C-enriched CO2 (δ13C=413.9‰) for 3 days to study the allocation and transformation of photosynthetic carbon to root biomass, water-soluble organic carbon (WSOC) in soil solution, and CO2 and CH4 entrapped in the soil. Elevated atmospheric CO2 concentration not only directly increased the biomass above ground and in the roots by photosynthesis, but also indirectly increased the amounts of CH4 and CO2 entrapped in the soil. Most of the CO2 was dissolved in soil solution, but in contrast most of the CH4 existed in soil bubbles. When rice was fed with 13C-enriched CO2 at the grain-filling stage of growth, the increase in 13C of entrapped CO2 under ambient CO2 conditions accounted for 1.476% of the increase in 13C of the rice plants and for 1.845% of the increase in 13C of rice plants grown under elevated CO2 conditions. The increase in 13C of entrapped CH4 accounted for 0.178% and 0.234% of the increase in 13C of rice plants grown under ambient and elevated CO2 treatments, respectively. Under conditions of elevated CO2 the entrapped 13C–CO2 and 13C–CH4 increased by 57% and 65%, respectively. The increase in 13C after feeding with 13C-enriched CO2, as a proportion of the total C of plants before feeding, was higher for CH4 entrapped in rice-paddy soil than for CO2 entrapped in rice-paddy soil, WSOC in soil solution, aboveground biomass, and root biomass under both ambient and elevated CO2 treatments. This indicates that during the grain-filling stage of rice growth, photosynthesized carbon had the most impact on CH4 production and accelerated the CH4 turnover rate. [Copyright &y& Elsevier]