Eclipse Effects on CO2 Profile within and above Sorghum Canopy

Abstract

We analyzed the effects of a partial solar eclipse (22 July 2009) on microclimate including vertical gradients of CO₂ concentrations ([CO₂]), so called [CO₂] profile, in a mature sorghum canopy. Together with CO₂ measurement, major photosynthetic drivers of microclimate, light intensity, temperature and atmospheric H₂O concentration ([H₂O]) were also measured simultaneously at the same place and height. [CO₂] at 6.0, 3.2, 2.1, 1.4, 0.7, 0 m above the ground (canopy height was 3.2 m) increased by 5.8, 4.8, 9.0, 7.8, 6.4, 7.6μmol mol-¹, respectively, from 1 hour before the eclipse maximum to the eclipse maximum, during which theincident solar radiation above the canopy dropped by 1473 μmol photons m-² s-¹. However, it declined by 3.4, 10.6, 10.8, 6.0, 5.4, and 5.8μmol mol-¹, respectively, from the eclipse to 1 hour later,during which the incident radiation increased by 1350μmol photons m-² s-¹. The [CO₂] profile during the eclipse was uniform except for higher [CO₂] near the ground. Comparative analysis of theeffect of light intensity on the microclimate during the eclipse-induced light decreasing phase (ELDP) and eclipse-induced light increasing phase (ELIP) revealed that [CO₂], [H₂O], temperature and relative humidity (RH) are significantly correlated with the light intensity above the canopy in a nearly linear fashion. Furthermore it indicated that detected less light-reacted canopy photosynthesis at a higher layer within the canopy during ELIP might be due to slower response of stomatal opening (than closing) to the light intensity above the canopy.     

Effects of atmospheric CO2 concentration and defoliation on the growth of Themeda triandra

The effects of elevated atmospheric carbon dioxide (CO₂) concentration (700 μmol mol^?1) on defoliated (three clippings at 3‐week intervals) and undefoliated plants were determined for the C₄ grass Themeda triandra, Forsk. The elevated CO₂ concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO₂ concentration treatment. The primary effect of the elevated CO₂ concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down‐regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO₂ concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO₂ concentration treatment were lost following a final 3‐week reversion to ambient CO₂ concentration, but occurred in plants exposed to the elevated CO₂ concentration for the final 3‐week period only. In conclusion, elevated atmospheric CO₂ concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO₂ responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation.     

Impacts of early-season square abscission on the growth and yield of transgenic Bt cotton under elevated CO2

A field study was carried out to quantify the compensation capacity of Bacillus thuringiensis (Bt)-transgenic cotton to simulated damage by manually removing squares during the early growing season in 2004 and 2005 in combination with CO₂ levels (ambient CO₂ and elevated CO₂). Treatments included: initial squares were wholly (100%) removed manually for 1 week (i.e., SR1 treatment) and for 2 consecutive weeks (i.e., SR2 treatment). Plant leaf area was measured every 2 weeks, and plant root, stem, leaf, shatters, boll dry weight and lint yield and maturity were measured at harvest. Significantly higher leaf area per plant was observed on each sampling date for SR1 and SR2 treatments compared with control (SR0) treatment in 2004 and 2005 under elevated CO₂. Significantly higher lint yield and maturity were observed for SR0, SR1 and SR2 treatments under elevated CO₂ in 2004 and 2005. CO₂ concentration and square removal significantly affected plant lint yield and maturity. Moreover, the interaction between CO₂ concentration × square removal had a significant effect on plant leaf dry weight, lint yield and maturity. Our results indicated that transgenic cotton plants can compensate for the manual removal of 100% of the initial squares for 1 and 2 weeks under ambient and elevated CO₂.     

Effects of free air carbon dioxide enrichment and nitrogen supply on growth and yield of winter barley cultivated in a crop rotation

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate growth of C₃ crops. Although barley is one of the important cereals of the world, little information exists about the effect of elevated [CO₂] on grain yield of this crop, and realistic data from field experiments are lacking. Therefore, winter barley was grown within a crop rotation over two rotation cycles (2000 and 2003) at present and elevated [CO₂](375 ppm and 550 ppm) and at two levels of nitrogen supply (adequate (N2): 262 kg ha⁻¹ in 1st year and 179 kg ha⁻¹ in 2nd year) and 50% of adequate (N1)). The experiments were carried out in a free air CO₂ enrichment (FACE) system in Braunschweig, Germany. The reduction in nitrogen supply decreased seasonal radiation absorption of the green canopy under ambient [CO₂] by 23%, while CO₂ enrichment had a positive effect under low nitrogen (+8%). Radiation use efficiency was increased by CO₂ elevation under both N levels (+12%). The CO₂ effect on final above ground biomass was similar for both nitrogen treatments (N1: +16%; N2: +13%). CO₂ enrichment did not affect leaf biomass, but increased ear and stem biomass. In addition, final stem dry weight was higher under low (+27%) than under high nitrogen (+13%). Similar findings were obtained for the amount of stem reserves available during grain filling. Relative CO₂ response of grain yield was independent of nitrogen supply (N1: +13%; N2: +12%). The positive CO₂ effect on grain yield was primarily due to a higher grain number, while changes of individual grain weight were small. This corresponds to the findings that under low nitrogen grain growth was unaffected by CO₂ and that under adequate nitrogen the positive effect on grain filling rate was counterbalanced by shortening of grain filling duration.     

Comparison of petiole nitrate concentrations,SPAD chlorophyll readings,and QuickBird satellite imagery in detecting nitrogen status of potato canopies

Nitrogen (N) management is critical in optimizing potato yield and quality and reducing environmental pollution. Six N rates from 34 to 270 kg ha⁻¹, and different timing of N application were used in a 3-year field experiment to contrast SPAD-502 chlorophyll meter and QuickBird satellite imagery data against the conventional petiole sampling technique for assessing canopy N status. Overall treatment variations in SPAD readings were consistent with those in petiole nitrate-nitrogen (NO₃-N) concentrations. However, the ability of the SPAD meter to detect treatment differences varied with growth stage and growing season. Severe N deficiency was detected about 1 month after emergence with SPAD readings, but as early as 2 weeks after emergence with petiole NO₃-N concentrations. Petiole NO₃-N concentrations tended to differentiate more treatment variations than SPAD readings at all growth stages except at hilling. N deficiency was detected with QuickBird image-derived vegetation indices (VIs) at the hilling stage in 2002, but not in 2003. At the post-hilling stage, treatment differences in VI values were minimal and insignificant except very late in the growing season. SPAD meters could be used as an indirect method for detecting N deficiency at the hilling stage when making supplemental N applications, but they are not as sensitive as the petiole sampling method. The sensitivity of QuickBird imagery to canopy N variations needs to be further tested with more pixel data. However, cloud interference and high cost of images could limit the use of QuickBird data in making timely management decisions.     

Production Ecophysiology of Hungarian Green Pepper Under Elevated Air CO2 Concentration

SUMMARY

Production, dry matter (including reproductive) allocation, photosynthesis, transpiration, water use efficiency and carbon and nitrogen responses of a Hungarian sweet pepper (Capsicum annum L.) under continuous elevated CO₂ concentrations are reported. Plants were grown in open top chambers under a temperate-continental climate in Hungary from plantation at ambient (350 μmol mol^?1) and elevated (700 μmol mol^?1) CO₂ concentrations. The CO₂ assimilation responses of the green pepper plants grown in high CO₂ from plantation until final harvest reflected down-regulation of their photosynthesis. The integrated and combined effect of the increased net CO₂ assimilation rate and the unchanged rate of transpiration resulted in higher WUE at elevated CO₂ concentrations in the high CO₂ plants than in the control ones grown at ambientCO₂. However, the improved water use efficiency in the high CO₂ plants was not followed by an acclimation in C-trans-location and C-allocation to the reproductive organs in the required degree. This was reflected in a slightly increased overall plant production and higher reproductive allocation, but was not accompanied by an increased fresh or dry berry mass production. The acclimation discussed may be of advantage for plant growth in a high CO₂ environment with restricted water availability. We did not find worthy statistical difference between the yield mass of the control and elevated CO₂, although the dry matter production parameters of the high CO₂ plants had statistically not significantly higher values.     

Yield formation of CO2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice (Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO₂] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO₂ enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol⁻¹) [CO₂] under two levels of supplemental N (12.5 g Nm⁻² and 25 g Nm⁻²). Elevated [CO₂] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO₂] was independent of N fertilization, but varied among different years. On average, elevated [CO₂] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO₂], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO₂], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO₂] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO₂] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO₂] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO₂] levels.     

Simulation of the effects of genotype and N availability on rice growth and yield response to an elevated atmospheric CO2 concentration

The objective of this study was to identify physiological processes that result in genotypic and N fertilization effects on rice yield response to elevated atmospheric CO₂ concentrations ([CO₂]). This study conducted growth and yield simulations for 9 rice genotypes grown at 4 climatically different sites in Asia, assuming the current atmospheric [CO₂] (360 ppm) and elevated [CO₂] (700 ppm) using 5 levels of N fertilizer (4, 8, 12, 16, 20 g m⁻² N fertilizer). A rice growth model that was developed and already validated for 9 different genotypes grown under 7 sites in Asia was used for the simulation, integrating additional components into the model to explain the direct effect of [CO₂] on several physiological processes. The model predicted that the relative yield response to elevated [CO₂] (RY, the ratio of yield under 700 ppm [CO₂] to that under 360 ppm [CO₂]) increased with increasing N fertilizer, ranging from 1.12 at 4 g m⁻² N fertilizer to 1.22 at 20 g m⁻² N fertilizer, averaged overall genotypes and locations. The model also predicted a large genotypic variation in RY at the 20 g N treatment, ranging from 1.08 for ‘WAB450-I-B-P-38-HB’ to 1.41 for ‘Takanari’ averaged overall locations. Combining all genotypes grown at the 5N fertilization conditions, a close 1:1 relationship was predicted between RY and the relative [CO₂] response in spikelet number for crops with a small number of spikelets (less than 30,000 m⁻²) under the current atmospheric [CO₂] (n = 18, r = 0.89^***). In contrast, crops with a large number of spikelets under the current atmospheric [CO₂] showed a significantly larger RY than the relative [CO₂] response for spikelet number per unit area. The model predicted that crops with a larger number of spikelets under the current atmospheric [CO₂] derived great benefit from elevated [CO₂] by directly allocating increased carbohydrate to their large, vacant sink, whereas crops with a smaller number of spikelets primarily required an increased spikelet number to use the increased carbohydrate to fill grains. The simulation analyses suggested that rice with a larger sink capacity relative to source availability under the current atmospheric [CO₂] showed a larger yield response to elevated [CO₂], irrespective of whether genotype or N availability was the major factor for the large sink capacity under the current [CO₂]. The model predicted that the RY response to nitrogen was brought about through the N effects on spikelet number and non-structural carbohydrate accumulation. The genotypic variation in RY was related to differences in spikelet differentiation efficiency per unit plant N content. Further model validation about the effects of [CO₂] on growth processes is required to confirm these findings considering data from experimental studies.     

Enhanced dormancy release and emergence from potato tubers after exposure to a controlled atmosphere

The North American potato industry requires an effective and environmentally-appropriate, dormancy-release methodology. The present study examined dormancy release and subsequent sprout emergence based on a modified, controlled-atmosphere (CA) approach using such environmentallycompatible gases as nitrogen, carbon dioxide and oxygen with or without trace amounts of ethylene (50 ppm). This paper is the first published report of a semi-automated, controlled-atmosphere system for dormancy release of potato tubers. The system allows computer-controlled gas application and analysis for up to four gas mixtures simultaneously. Low oxygen concentrations (< 10%) for 10 days in the presence of 10 to 60% carbon dioxide or a high carbon dioxide (60%)/oxygen (40%) treatment caused tuber breakdown regardless of cultivar. The most effective mixtures for enhanced dormancy release and sprout emergence were 20% CO₂/40% O₂ or 60% CO₂/18-20% O₂ and their effects were further enhanced by 50 ppm C₂H₄ (ethylene). In the presence of 50 ppm C₂H₄ the 20% CO2/40% O₂ mixture was comparable to bromoethane in effectiveness. Temperature and light exposure affected subsequent Russet Burbank tuber responses to CO₂/O₂/C₂H₄ gas mixtures.     

Evaluation of the Effect of Photosynthesis on Biomass Production with Simultaneous Analysis of Growth and Continuous Monitoring of CO2 Exchange in the Whole Plants of Radish,cv Kosena under Ambient and Elevated CO2

Abstract

The effects of elevated CO₂ (approximate doubling of atmospheric CO₂ concentration) on the rate of photosynthesis estimated from continuous monitoring of CO₂ exchange in whole plants were investigated in radish cv. Kosena accompanied with simultaneous analysis of growth for 6 days from 15 to 21 days after planting (DAP). The elevated CO₂ increased the dry weights of hydroponically grown radish plants by 59% at 21 DAP.

The increase in dry weight was due to a combined effect of increased leaf area and increased photosynthetic rate per unit leaf area. Leaf area and the photosynthetic rate were increased by elevated CO₂ by 18-43% and 9-20%, respectively, during 15 to 21 DAP. Namely, an increase in the rate of photosynthesis is accompanied by an increase in leaf area, both having a significant effect on biomass production.     

CO2 Enrichment Effects on Forage and Grain Nitrogen Content of Pasture and Cereal Plants

SUMMARY

Increasing atmospheric CO₂ concentrations [CO₂] have the potential to enhance growth and yield of agricultural plants. Con-comitantly plants grown under high [CO₂] show significant changes of the chemical composition of their foliage and of other plant parts. Particularly, high [CO₂] result in a decrease of plant nitrogen (N) concentration, which may have serious consequences for crop quality. This presentation summarizes the results of a variety of CO₂ enrichment studies with pasture plants (Lolium spp., Trifolium repens) and cereal species (Triticum aestivum, Hordeum vulgare) which were conducted at our laboratory under different growth and CO₂ exposure conditions ranging from controlled environment studies to investigations under free air carbon dioxide enrichment (FACE). With the exception of clover in all experiments a CO₂-induced decline of forage and grain N concentration was observed. The magnitude of this reduction differed between species, cultivars, management conditions (N fertilization) and CO₂ exposure conditions. No unambiguous evidence was obtained whether N fertilization can contribute to meet the quality requirements for cereals and grass monocultures with respect to tissue N concentrations in a future high-CO₂ world. As shown in the FACE experiments current application rates of N fertilizers are inadequate to achieve quality standards.     

玉米氮、磷、钾、水和二氧化碳资源积累与利用的Meta分析

按照Meta分析原理,汇集近年来的玉米田间试验数据共722组,进行稳健统计、梯度和等值线分析。氮、磷、钾、水和二氧化碳共5个数据集的玉米产量中位数变化在7.91~10.61 t/hm2之间,生产百公斤玉米子粒N、P2O5、K2O、CO2、H2O的资源需求量分别为1.98、0.85、2.12、298.8 kg和44.2 m3。产量偏导数比值(资源利用效率的偏导数/积累量的偏导数)有3种表现,水与氮归为一类,产量偏导数比值大多数都在1/2以下,少数值为1,说明在大多数情况下,积累量的增产作用是资源利用效率的2倍以上,少数情况下二者作用相当;钾与磷为一类,产量偏导数比值以1最多,1/2和2次之,说明以资源利用效率和积累量的作用相当为主,但是,也有不少利用效率的作用是积累量的2倍以上,或者相反;二氧化碳绝大多数产量偏导数比值在2以上,较少部分的值为1,说明在绝大多数情况下资源利用效率的增产作用是积累量的2倍以上,少数情况下二者作用相当。当代玉米百公斤子粒的资源需求量明显下降,资源积累(消耗)量和利用效率对产量的相对重要性因二者组合所处的区域而异,不同资源因子对产量的作用格局不同。     

Implications of Elevated CO2-Induced Changes in Agroecosystem Productivity

SUMMARY

Since CO₂ is a primary input for crop growth, there is interest in how increasing atmospheric CO₂ will affect crop productivity and alter cropping system management. Effects of elevated CO₂ on grain and residue production will be influenced by crop selection. This field study evaluated soybean [C₃; Glycine max(L.) Merr.] and grain sorghum [C₄; Sorghum bicolor (L.) Moench.] cropping systems managed under conservation tillage practices and two atmospheric CO₂ concentrations (ambient and twice ambient) for three growing seasons. Elevated CO₂ increased soybean and sorghum yield by 53% and 17% increase, respectively; reductions in whole plant water use were also greater for soybean than sorghum. These findings suggest that increasing CO₂ could improve future food security, especially in soybean production systems. Elevated CO₂ increased aboveground residue production by > 35% for both crops; such shifts could complement conservation management by increasing soil surface cover, thereby reducing soil erosion. However, increased residue could negatively impact crop stand establishment and implement effectiveness during tillage operations. Elevated CO₂ increased total belowground dry weight for both crops; increased root proliferation may alter soil structural characteristics (e.g., due to increased number and extent of root channels) which could lead to increases in porosity, infiltration rates, and subsequent soil water storage. Nitrate leaching was reduced during the growing season (due to increased N capture by high CO₂-grown crops), and also during the fallow period (likely a result of altered decomposition patterns due to increased C:N ratios of the high CO₂-grown material). Enhanced crop growth (both above-and be-lowground) under elevated CO₂ suggests greater delivery of C to soil, more soil surface residue, and greater percent ground coverage which could reduce soil C losses, increase soil C storage, and help ameliorate the rise in atmospheric CO₂. Results from this study suggests that the biodegradability of crop residues and soil C storage may not only be affected by the environment they were produced in but may also be species dependent. To more fully elucidate the relationships between crop productivity, nutrient cycling, and decomposition of plant materials produced in elevated CO₂ environments, future studies must address species effects (including use of genetically modified crops) and must also consider other factors such as cover crops, crop rotations, soil series, tillage practices, weed management, and regional climatic differences.     

Interactive Effects of CO2 and O3 on the Growth of Trisetum flavescens and Trifolium pratense Grown in Monoculture or a Bi-Species Mixture

SUMMARY

Golden oat grass (Trisetum flavescens L.) and red clover (Trifolium pratense L.) were grown as monocultures or bi-species mixtures under controlled conditions and exposed to ambient (350 ppm) or elevated (580 ppm) CO₂, with or without addition of O₃ (diel profile with 150 ppb maximum). Shoot biomass measurements after the initial growth and two re-growth periods were used to determine the specific responses of both species, and the difference in the specific response between monocultures and mixtures. T. pratense was much more responsive to CO₂, O₃, and their combination, compared to T. flavescens. In the case of O₃ but not of CO₂, the difference in sensitivity between species was larger in mixture than in monoculture. In contrast to elevated CO₂, O₃ significantly reduced the root:shoot ratio in the mixture, which could explain the increasing negative effect of O₃ on clover with progressing harvests.

The relative CO₂ stimulation of T. pratense and of the cumulative mixture shoot biomass was larger in the presence than in the absence of O₃, which was due to an almost complete protection from O₃ stress by elevated CO₂. In the mixture, the fraction of T. flavescens was small and increased during the experiment; this increase was most pronounced with O3, but any change in mixture biomass was dominated by the response of T. repens.

The results confirm that in grass/legume mixtures legumes are most sensitive to elevated CO₂ and O₃, but the magnitude of specific responses depends on canopy structure and of plant development. Elevated CO₂ minimizes the negative impacts of O₃ stress on above- and below-ground plant growth.     

Design and Synthesis of Novel Xyloketal Derivatives and Their Protective Activities against H2O2-Induced HUVEC Injury

In this work, we designed and synthesized a series of amide derivatives (1–13), benzoxazine derivatives (16–28) and amino derivatives (29–30) from xyloketal B. All 28 new derivatives and seven known compounds (14, 15, 31–35) were evaluated for their protection against H₂O₂-induced HUVEC injury. 23 and 24 exhibited more potential protective activities than other derivatives; and the EC₅₀ values of them and the leading compound 31 (xyloketal B) were 5.10, 3.59 and 15.97 μM, respectively. Meanwhile, a comparative molecular similarity indices analysis (CoMSIA) was constructed to explain the structural activity relationship of these xyloketal derivatives. This 3D QSAR model from CoMSIA suggested that the derived model exhibited good predictive ability in the external test-set validation. Derivative 24 fit well with the COMSIA map, therefore it possessed the highest activity of all compounds. Compounds 23, 24 and 31 (xyloketal B) were further to examine in the JC-1 mitochondrial membrane potential (MMP) assay of HUVECs using flow cytometry (FCM). The result indicated that 23 and 24 significantly inhibited H₂O₂-induced decrease of the cell mitochondrial membrane potential (ΔΨm) at 25 μM. Collectively, the protective effects of xyloketals on H₂O₂-induced endothelial cells may be generated from oxidation action by restraining ROS and reducing the MMP.     

Carbon dioxide enrichment and temperature effects on cotton canopy photosynthesis,transpiration, and water-use efficiency

The objectives of this study were to evaluate effects of ambient and double ambient [CO₂] at a range of growing temperatures on photosynthesis, respiration, transpiration, water-use efficiency and dry matter accumulation of cotton plants (Gossypium hirsutum L., cv. DPL 50). In Experiment I, plants were grown outdoors until first bloom, then transferred into naturally lit growth chambers and grown for 22 days at 30/18°C with five CO₂ concentrations varying from 350 to 900 μl l⁻¹. In Experiment II, air temperatures were maintained at 20/12, 25/17, 30/22, and 35/27°C day/night during a 70-day experimental period with [CO₂] of 350 and 700 μl l⁻¹ at each temperature. Photosynthesis increased with [CO₂] from 350 to 700 μl l⁻¹ and with temperature. Plants grown at 35/27°C produced fewer bolls due to abscission compared with plants grown at optimum temperatures (30/20°C). At higher [CO₂], water-use efficiency increased at all temperatures due mainly to increased canopy photosynthesis but also to more limited extent to reduced canopy transpiration. Increased photosynthesis at higher [CO₂] resulted in greater dry matter accumulation at all temperatures except at 20/12°C. Respiration increased as dry matter and temperature increased. Plants grown at higher [CO₂] had less respiration per unit dry matter but more per unit area. These results indicate that future increases in [CO₂] are likely to benefit cotton production by increasing carbon assimilation under temperatures favorable for cotton growth. Reduced fruit weights at higher temperatures indicate potential negative effects on production if air temperatures increase as projected in a high-CO₂ world.     

Effects of elevated CO2 concentration on growth and photosynthesis of Chinese yam under different temperature regimes

Chinese yam (‘yam’) was grown at different carbon dioxide concentrations ([CO₂]), namely, ambient and elevated (ambient + 200 μmol mol^?1), under low- and high-temperature regimes in summer and autumn, separately. For comparison, rice was also grown under these conditions. Mean air temperatures in the low- and high-temperatures were respectively 24.1 and 29.1 °C in summer experiment and 20.2 and 24.9 °C in autumn experiment. In summer experiment, yam vine length, leaf area, leaf dry weight (DW), and total DW were significantly higher under elevated [CO₂] than ambient [CO₂] in both temperature regimes. Additionally, number of leaves, vine DW, and root DW were significantly higher under elevated [CO₂] than under ambient [CO₂] in the low-temperature regime. In autumn experiment, tuber DW was significantly higher under elevated [CO₂] than under ambient [CO₂] in the high-temperature regime. These results demonstrate that yam shows positive growth responses to elevated [CO₂]. Analysis of variance revealed that significant effect of [CO₂] × air temperature interaction on yam total DW was not detected. Elevated-to-ambient [CO₂] ratios of all growth parameters in summer experiment were higher in yam than in rice. The results suggest that the contribution of elevated [CO₂] is higher in yam than in rice under summer. Yam net photosynthetic rate was significantly higher under elevated [CO₂] than under ambient [CO₂] in both temperature regimes in summer. Elevated [CO₂] significantly affected on the rate in yam but not in rice in both experiments. These findings indicate that photosynthesis responds more readily to elevated [CO₂] in yam than in rice.     

Effect of Altitude on the Response of Net Photosynthetic Rate to Carbon Dioxide Increase by Spring Wheat

Abstract: The partial pressure of CO₂ in air decreases with the increase in altitude. Therefore, increase in molar concentration of CO₂ is smaller at higher altitudes than at lower altitudes for increases in molar fraction of CO₂. This study aimed to predict the effect of global CO₂ increase on net photosynthetic rateof spring wheat (Triticum aestivum L.) at high altitudes. The net photosynthetic rate of spring wheat grown in Lhasa (3688 m above sea level), China, was compared with that of the same cultivar grown in Sapporo (15 m above sea level), Japan. At the current level of CO₂, it was significantly lower in Lhasa than in Sapporo, and stomatal conductance, chlorophyll content (SPAD value) and apparent quantum yield were similar in both locations. The interaction ofCO₂ level and altitude was suggested; the amount of increase in net photosynthetic rate caused by increase in CO₂ was smaller at high altitudes than at low altitudes. Lower CO₂ partial pressure at higher altitude could explain the difference in net photosynthetic rate between altitudes, and the interaction of CO₂ level and altitude.     

Heat-tolerant rice cultivars retain grain appearance quality under free-air CO2 enrichment

Background

Heat-tolerant rice cultivars have been developed as a countermeasure to poor grain appearance quality under high temperatures. Recent studies showed that elevated CO₂ concentrations (E-[CO₂]) also reduce grain quality. To determine whether heat-tolerant cultivars also tolerate E-[CO₂], we conducted a free-air CO₂ enrichment (FACE) experiment with 12 rice cultivars differing in heat tolerance.

Results

The percentage of undamaged grains of five standard cultivars (Akitakomachi, Kinuhikari, Koshihikari, Matsuribare, Nipponbare) averaged 61.7% in the ambient [CO₂] (AMB) plot and 51.7% in the FACE plot, whereas that of heat-tolerant cultivars (Eminokizuna, Wa2398, Kanto 257, Toyama 80, Mineharuka, Kanto 259, Saikai 290) averaged 73.5% in AMB and 71.3% in FACE. This resulted in a significant [CO₂] by cultivar interaction. The percentage of white-base or white-back grains increased from 8.4% in AMB to 17.1% in FACE in the sensitive cultivars, but from only 2.1% in AMB to only 4.4% in FACE in the heat-tolerant cultivars.

Conclusion

Heat-tolerant cultivars retained their grain appearance quality at E-[CO₂] under present air temperatures. Further improvements in appearance quality under present conditions will be needed to achieve improvements under E-[CO₂], because E-[CO₂] will likely lower the threshold temperature for heat stress.