Abstract. There is some evidence that rice cultivars respond differently to elevated CO 2 concentrations ([CO 2 ]), but [CO 2 ] Â cultivar interaction has never been tested under open-field conditions across different sites. Here, we report on trials conducted at free-air CO 2 enrichment (FACE) facilities at two sites in Japan, Shizukuishi (2007 and2008) and Tsukuba (2010). The average growing-season air temperature was more than 5 C warmer at Tsukuba than at Shizukuishi. For four cultivars tested at both sites, the [CO 2 ] Â cultivar interaction was significant for brown rice yield, but there was no significant interaction with site-year. Higher-yielding cultivars with a large sink size showed a greater [CO 2 ] response. The Tsukuba FACE experiment, which included eight cultivars, revealed a wider range of yield enhancement (3-36%) than the multi-site experiment. All of the tested yield components contributed to this enhancement, but there was a highly significant [CO 2 ] Â cultivar interaction for percentage of ripened spikelets. These results suggest that a large sink is a prerequisite for higher productivity under elevated [CO 2 ], but that improving carbon allocation by increasing grain setting may also be a practical way of increasing the yield response to elevated [CO 2 ].

Summary• A free air CO 2 enrichment (FACE) system in which rice was grown under elevated CO 2 conditions by releasing high pressure, pure CO 2 from emission tubes surrounding the crop is described here. Unlike other (FACE) systems, blowers were not used to mix the emitted CO 2 with the surrounding air.• Four 12-m diameter emission structures ('rings') were constructed. Monitoring and control of CO 2 emission was carried out by a series of CO 2 and wind sensors, data loggers, controllers and valves. The target CO 2 concentration ( [CO 2 ] ) was 200 µ mol mol -1 above ambient; enrichment was carried out continuously.• Temporal [CO 2 ] control was adequate, with c . 60 and 90% of the air samples at ring center having a [CO 2 ] within 10 and 20% of the target, respectively. Spatial [CO 2 ] distribution was also adequate, with 60% of the ring area having a [CO 2 ] that was within 15% of that at the center.• At comparable wind speeds, the pure CO 2 injection FACE system described here had a similar performance to that of FACE designs that use blowers to mix the injected CO 2 with the air.

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].

Paddy fields are an important source of atmospheric CH₄, the second most important greenhouse gas. There is a strong concern that the increasing atmospheric CO₂ concentration ([CO₂]) and global warming are further stimulating CH₄ emissions, but the magnitude of this stimulation varies substantially by study, and few open-field evaluations have been conducted. Here we report results obtained at a Japanese rice free-air CO₂ enrichment (FACE) site under water and soil temperature elevation during two growing seasons. Our objectives were to evaluate the effects of high [CO₂] (ambient + 200 μmol mol⁻¹) and elevated soil temperature (+ 2 °C) on CH₄ emissions under completely open-field conditions. We found about 80% enhancement in total seasonal emissions by the additive effects of FACE and warming, indicating a strong positive feedback effect of global warming. The enhancement in CH₄ emission from the FACE-effect alone (+ 26%) was statistically non-significant (P = 0.19). Nevertheless, observed positive correlations between CH₄ emissions and rice biomass agreed well with previous studies, suggesting that higher photosynthesis led to greater rhizodeposition, which then acted as substrates for methanogenesis. Soil warming increased the emission by 44% (P < 0.001), which was equivalent to a Q₁₀ of 5.5. Increased rice biomass by warming could only partly explain the enhanced CH₄ emissions, but stoichiometric analysis of the electron budget indicated that even a moderate enhancement in organic matter decomposition due to soil warming can cause a large increase in CH₄ production under conditions where Fe(III) reduction, which was little affected by soil warming, dominates electron-accepting processes. At later rice growth stages, advanced root senescence due to elevated temperature probably provided more substrate for methanogenesis. Our stoichiometric evaluation showed that in situ Fe reduction characteristics and root turnover in response to elevated temperature should be understood to correctly predict future CH₄ emissions from paddy fields under a changing climate. Challenges remain for determination of in situ root-exudation rate and its response to FACE and warming

The design progress in a compact low aspect ratio (low A) DEMO reactor, ‘SlimCS’, and its design issues are reported. The design study focused mainly on the torus configuration including the blanket, divertor, materials and maintenance scheme. For continuity with the Japanese ITER-TBM, the blanket is based on a water-cooled solid breeder blanket. For vertical stability of the elongated plasma and high beta access, the blanket is segmented into replaceable and permanent blankets and a sector-wide conducting shell is arranged inbetween these blankets. A numerical calculation indicates that fuel self-sufficiency can be satisfied when the blanket interior is ideally fabricated. An allowable heat load to the divertor plate should be 8 MW m−2 or lower, which can be a critical constraint for determining a handling power of DEMO.

Quantification of rhizodeposition (root exudates and root turnover) represents a major challenge for understanding the links between above-ground assimilation and below-ground anoxic decomposition of organic carbon in rice paddy ecosystems. Free-air CO 2 enrichment (FACE) fumigating depleted 13 CO 2 in rice paddy resulted in a smaller 13 C/ 12 C ratio in plant-assimilated carbon, providing a unique measure by which we partitioned the sources of decomposed gases (CO 2 and CH 4 ) into current-season photosynthates (new C) and soil organic matter (old C). In addition, we imposed a soil-warming treatment nested within the CO 2 treatments to assess whether the carbon source was sensitive to warming. Compared with the ambient CO 2 treatment, the FACE treatment decreased the 13 C/ 12 C ratio not only in the rice-plant carbon but also in the soil CO 2 and CH 4 . The estimated new C contribution to dissolved CO 2 was minor (ca. 20%) at the tillering stage, increased with rice growth and was about 50% from the panicle-formation stage onwards. For CH 4 , the contribution of new C was greater than for heterotrophic CO 2 production; ca. 40-60% of season-total CH 4 production originated from new C with a tendency toward even larger new C contribution with soil warming, presumably because enhanced root decay provided substrates for greater CH 4 production. The results suggest a fast and close coupling between photosynthesis and anoxic decomposition in soil, and further indicate a positive feedback of global warming by enhanced CH 4 emission through greater rhizodeposition.

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].

In vitro evolution was applied to obtain highly active mutants of Ralstonia eutropha polyester synthase (PhbC(Re)), which is a key enzyme catalyzing the formation of polyhydroxybutyrate (PHB) from (R)-3-hydroxybutyryl-CoA (3HB-CoA). To search for beneficial mutations for activity improvement of this enzyme, we have conducted multi-step mutations, including activity loss and intragenic suppression-type activity reversion. Among 259 revertants, triple mutant E11S12 was obtained as the most active one via PCR-mediated secondary mutagenesis from mutant E11 with a single mutation (Ser to Pro at position 80), which exhibited reduced activity (as low as 27% of the wild-type level) but higher thermostability compared to the wild-type enzyme. Mutant E11S12 exhibited up to 79% of the wild-type enzyme activity. Mutation separation of E11S12 revealed that the replacement of Phe by Ser at position 420 (F420S), located in a highly conserved alpha/beta hydrolase fold region, of the E11S12 mutant contributes to the improvement of the enzyme activity. A purified sample of the genetically engineered mutant, termed E11S12-1, with the F420S mutation alone was found to exhibit a 2.4-fold increase in specific activity toward 3HB-CoA, compared to the wild-type.