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Enhancing crop traits that increase grain yield under elevated CO2 concentrations is an important option for increasing the future productivity of rice. Here, we compared the growth and yield of five varieties with different genetic background under Free-Air CO2 Enrichment (FACE) conditions to identify traits responsible for varietal differences in yield increase under elevated CO2. Three high-yielding and two standard rice varieties grown under FACE conditions commonly had (1) shorter growth periods, (2) higher dry matter production, (3) higher numbers of spikelets (sink capacity) and panicles; and (4) higher yield than those grown under ambient CO2. Yield enhancement by elevated CO2 (FACE/Ambient), however, differed significantly among varieties, ranging from 1.10 to 1.25. The greater response of the sink capacity, defined as the product of spikelet number and single grain mass, was the main factor involved in yield increase. Three high-yielding varieties (Momiroman, Takanari, and Hokuriku 193) had greater sink capacity than two standard varieties and the sink capacity of these varieties significantly increased under FACE condition. However, yield enhancement in elevated CO2 was lower in Hokuriku 193 than in Momiroman and Takanari. In Hokuriku 193, sink production was relatively low while dry matter production was similar to the others. Therefore, larger increase in sink production efficiency per unit of dry matter production under FACE was found to be a particularly important varietal trait, suggesting that efforts to develop varieties suited to the predicted elevated CO2 condition should focus on this and the related traits. [ABSTRACT FROM AUTHOR]

Increasing night temperatures can reduce growth and yield of rice plants, but limited information is available on the comparative effects of high night temperature (HNT) treatment at different growth stages on growth and physiological responses of rice. We conducted a study in controlled-environment chambers to determine the growth and physiological responses and spikelet differentiation of rice cultivars to HNT treatment at different growth stages. Plants were exposed to two temperatures: 30/21 °C (low) and 30/25 °C (high) day/night temperatures. At the end of the vegetative period, plants grown in the low (LNT) and high (HNT) night temperatures were further subdivided and plants were exposed to different temperature treatments in the reproductive growth period. Photosynthesis, night respiration rates, and plant growth parameters were measured at various stages. High night temperature had no significant effects on the growth of rice cultivars during the vegetative phase. Maximum photosynthesis at the vegetative phase was not significantly affected, but plant dark respiration increased (within the 14–20% range). Genotypic variation in dark respiration was observed at later growth stages. Rice plants that received HNT at the early reproductive stage had the lowest number of spikelets per panicle, presenting a 35.9% of degenerated spikelets, significantly higher than those observed in other treatment times. This study shows that the response of rice cultivars to HNT varies with time of treatment and that the occurrence of HNT during the reproductive period provided supportive evidence on how HNT might reduce yield by increasing plant’s dark respiration rate and spikelet degeneration (which consequently reduced sink size), thus, decreasing biomass production. [ABSTRACT FROM AUTHOR]

Elevated CO 2 concentrations (E-[CO 2 ]) will likely increase grain yield but decrease grain protein content and increase grain chalkiness, thus degrading the grain quality of rice. Grain growth is the key process that determines both grain yield and quality, hence its responses to E-[CO 2 ] were studied in a free-air CO 2 enrichment (FACE) with the focus on variability among the spikelet positions within a panicle. We investigated the changes in grain growth in superior spikelets (SS) and inferior spikelets (IS) for three cultivars of rice differing in grain size and grain number: Akita 63, Koshihikari and Takanari. E-[CO 2 ] increased the grain yield by 15% across 2 years in the three cultivars. The grain growth responses were dependent on spikelet position: the grain mass was increased only in IS, while grain N content was reduced in SS but slightly increased in IS. The increase in IS grain mass was greatest in Takanari followed by Koshihikari with Akita 63 showing a slight decrease. E-[CO 2 ] significantly changed the occurrence of grain chalkiness, and the extent of the increased occurrence of basal white and white back kernels was greatest in Koshihikari followed by Akita 63 with Takanari being least affected. The varietal difference in the responses to E-[CO 2 ] should be studied further with respect to the variability of grain growth and distribution of carbon and nitrogen within a panicle for taking better advantages of the increasing [CO 2 ] for rice grain yield and quality in the future. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to elucidate the composition of bacterial communities from the soil, and endosphere and phyllosphere of upper and lower leaves and clarify the responses to elevated CO and/or soil temperature. Methods: Using 454 pyrosequencing, the 16S rRNA gene was analyzed from various bacterial communities in a rice paddy that was exposed to different atmospheric CO concentrations (ambient, +200 μmol.mol) and soil temperatures (ambient, +2 °C). Results: The treatments of elevated temperature and elevated CO plus temperature exerted significant influence on the structure of bacterial communities from the lower leaf endosphere. A significant influence of elevated CO plus temperature on the community structure was also observed in the upper leaf phyllosphere. The richness and diversity of bacterial communities from the lower leaf phyllosphere, upper leaf endosphere, and upper leaf phyllosphere were significantly affected by elevated CO plus temperature. However, we did not observe any significant influence of all climate change treatments (elevated CO, elevated temperature, and their combination) on the richness, diversity, and structure of soil bacterial communities. We also did not observe any significant effect of the single factor, elevated CO, on the structure of the leaf endosphere and phyllosphere bacterial communities. Enterobacteriaceae and Xanthomonadaceae were the most shifted phylotypes in response to elevated temperature and elevated CO plus temperature. Conclusions: Soil bacterial communities were more resistant to the tested climate change factors compare with foliar bacterial communities. Temperature was a more important factor in shaping the structure of foliar bacterial communities compared with CO. The response of leaf-associated bacterial communities could be influenced by the leaf location (upper leaf or lower leaf) within the rice plants and by the habitats (leaf endosphere or phyllosphere). [ABSTRACT FROM AUTHOR]

The development of crops which are well suited to growth under future environmental conditions such as higher atmospheric CO2 concentrations ([CO2]) is essential to meeting the challenge of ensuring food security in the face of the growing human population and changing climate. A high-yielding indica rice variety (Oryza sativa L. cv. Takanari) has been recently identified as a potential candidate for such breeding, due to its high productivity in present [CO2]. To test if it could further increase its productivity under elevated [CO2] (eCO2), Takanari was grown in the paddy field under season-long free-air CO2 enrichment (FACE, approximately 200 µmol mol−1 above ambient [CO2]) and its leaf physiology was compared with the representative japonica variety ‘Koshihikari’. Takanari showed consistently higher midday photosynthesis and stomatal conductance than Koshihikari under both ambient and FACE growth conditions over 2 years. Maximum ribulose-1,5-bisphosphate carboxylation and electron transport rates were higher for Takanari at the mid-grain filling stage in both years. Mesophyll conductance was higher in Takanari than in Koshihikari at the late grain-filling stage. In contrast to Koshihikari, Takanari grown under FACE conditions showed no decrease in total leaf nitrogen on an area basis relative to ambient-grown plants. Chl content was higher in Takanari than in Koshihikari at the same leaf nitrogen level. These results indicate that Takanari maintains its superiority over Koshihikari in regards to its leaf-level productivity when grown in elevated [CO2] and it may be a valuable resource for rice breeding programs which seek to increase crop productivity under current and future [CO2]. [ABSTRACT FROM AUTHOR]

To enable prediction of future rice production in a changing climate, we need to understand the interactive effects of temperature and elevated [CO2] (E[CO2]). We therefore examined if the effect of E[CO2] on the light-saturated leaf photosynthetic rate (Asat) was affected by soil and water temperature (NT, normal; ET, elevated) under open-field conditions at the rice free-air CO2 enrichment (FACE) facility in Shizukuishi, Japan, in 2007 and 2008. Season-long E[CO2] (+200 µmol mol−1) increased Asat by 26%, when averaged over two years, temperature regimes and growth stages. The effect of ET (+2°C) on Asat was not significant at active tillering and heading, but became negative and significant at mid-grain filling; Asat in E[CO2]–ET was higher than in ambient [CO2] (A[CO2])–NT by only 4%. Photosynthetic down-regulation at E[CO2] also became apparent at mid-grain filling; Asat compared at the same [CO2] in the leaf cuvette was significantly lower in plants grown in E[CO2] than in those grown in A[CO2]. The additive effects of E[CO2] and ET decreased Asat by 23% compared with that of A[CO2]–NT plants. Although total crop nitrogen (N) uptake was increased by ET, N allocation to the leaves and to Rubisco was reduced under ET and E[CO2] at mid-grain filling, which resulted in a significant decrease (32%) in the maximum rate of ribulose-1,5-bisphosphate carboxylation on a leaf area basis. Because the change in N allocation was associated with the accelerated phenology in E[CO2]–ET plants, we conclude that soil and water warming accelerates photosynthetic down-regulation at E[CO2]. [ABSTRACT FROM AUTHOR]

Studies showed that elevated [CO] would improve photosynthetic rates and enhance yields of rice; however, few studies have focused on the response of rice lodging, which is a major cause of cereal yield loss and quality reduction, under elevated [CO]. In this study, we examined the effects of elevated [CO] on stem and root lodging using 4 rice cultivars (86Y8, japonica hybrid; LYP9, 2-line indica hybrid; variety 9311, type of indica inbred rice, and SY63, 3-line indica hybrid) grown under two [CO] levels: 400 and 680 μmol mol. Our results indicated that under elevated [CO], the stem-lodging risk (SLR) of 9311 decreased, while in SY63 the SLR increased, 86Y8 and LYP9 were not significantly affected; the risk of root lodging was reduced for all cultivars, because root biomass (instead of root number) and bending strength were increased significantly, and then the increase of anti-lodging ability is far higher than that of self-weight mass moment for all cultivars. These findings suggested that higher [CO] can enhance the risk of stem-lodging for cultivars with strong-[CO]-responses, but may not aggravate the root lodging for all rice cultivars. [ABSTRACT FROM AUTHOR]