Temperature Gradient Chambers Research Articles

Effect of high night temperature on leaf senescence, physiological activity, and growth in soybean

Physiological processes that cause a negative growth response to high night temperatures (HNTs) were investigated in soybean. An HNT (28​°C) was established in a phytotron during the first (HL) and second (LH) halves of the reproductive stage and the entire (HH) reproductive stage, along with a continuously low (LL) night temperature (22​°C). Plant biomass was lower in HH than that in LL, whereas the harvest index was relatively stable. N accumulation in the plants tended to decline with HNT. The leaf area and leaf N concentration tended to be lower in HL and HH than in LL, suggesting an earlier onset of leaf senescence under HNT in the early reproductive stage. The light-saturated leaf photosynthetic rate was lower in HH than in LL during the late reproductive stage, associated with a low stomatal conductance and leaf photosynthetic rate per intercellular CO2 concentration. A slower rise in the leaf photosynthetic rate in the morning occurred likely because of the HNT, coinciding with the low leaf water potential at predawn and low leaf photosynthetic rate to intercellular CO2 concentration ratio. A moderately increasing gradient of night temperature from 21.7 to 23.9​°C was created in a mini-field in another experiment using a temperature gradient chamber, and in this experiment, crop growth and N dynamics were similar to those obtained in the phytotron study. These results suggest that the biomass growth of soybean is affected by HNT, particularly during the early reproductive stage.

Independent and interactive effects of eCO2 and eTemp. on Spodoptera frugiperda (J E Smith) on Maize-A major input for prediction of future pest scenario

Climate change is now unequivocal and influences crops and the incidence of insect pests. Understanding the spatially variable, species-specific, and complex effects of climate change is essential in developing an appropriate pest management strategy. The two dimensions of climate change i.e., elevated temperature (eTemp.) and elevated CO2 (eCO2) influence insect herbivores. In the present study, the growth and development of an invasive insect pest, fall armyworm, Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae) on maize at eCO2 and eTemp conditions using CO2 and temperature Gradient Chambers (CTGC) was estimated. Dilution of bio-chemical constituents was noted with lower leaf nitrogen (9%–14%), higher carbon (3%–11%), higher C : N (18%–26%), and higher tannins (13%) in maize foliage at eCO2+eTemp levels. A significant influence on primary parameters of insect viz., higher total consumption by larvae (38%), extended larval duration (13%) with increased larval weights (17%), and differential pupal weights (14%) in successive generations was recorded at eCO2 + eTemp compared to ambient. Their effect was continued on various insect performance indices also, with higher relative consumption rate, RCR (40%), lower relative growth rate, RGR (11%), and varied approximate digestibility (AD), the efficiency of conversion of ingested food (ECI) and digested food (ECD) of S frugiperda larvae. The interactive effect of eCO2 and eTemp led to a higher Potential Population Increase Index (PPII) (19%) due to higher fecund adults. The effect of eCO2 offsets the impact of eTemp when interacting together on some of the insect parameters. The present results indicate that eCO2 and eTemp play a key role in influencing the growth and development of S frugiperda indicating higher pest incidence in future climate change periods.

Factors causing the increase in arsenic concentration in brown rice due to high temperatures during the ripening period and its reduction by applying converted furnace slag

It has been pointed out that the concentration of arsenic (As) in brown rice increases due to high temperatures during the ripening period, and fertilization that can reduce As in brown rice even under high-temperature is required. The effectiveness of using converted furnace slag (CFS) to reduce the As concentration in brown rice was investigated. Rice plants were cultivated in Wagner pots (1/5000a) filled with gray lowland soil added CFS under ambient conditions up to 1 week after heading. Those pots were moved to a temperature gradient chamber set at four temperature levels (ambient, mildly-high, moderate-high, and super-high) and kept until harvest. An analysis of covariance using the mean daytime temperature as a covariate showed significant linearity of regression for As concentrations, indicating that high temperature increased the concentration of As in brown rice. The application of 30 g of CFS significantly reduced 20% of the As concentration in the rice, suggesting that CFS can be an effective countermeasure to reduce the As concentration in brown rice under high-temperature conditions. Since inorganic As flows into brown rice through sieve tubes, the cause of the increase in As concentration in brown rice due to high temperature was investigated by comparing the concentrations with carbon dynamics. The significant positive correlation between the As/carbon ratio and the As concentration in brown rice was observed, suggesting that high temperature reduces the rate of carbon translocation which is one of the essential factors in the increase in As concentration in brown rice due to high temperature.

Temperature-sensitive migration dynamics in neutrophil-differentiated HL-60 cells

Cell migration plays an essential role in wound healing and inflammatory processes inside the human body. Peripheral blood neutrophils, a type of polymorphonuclear leukocyte (PMN), are the first cells to be activated during inflammation and subsequently migrate toward an injured tissue or infection site. This response is dependent on both biochemical signaling and the extracellular environment, one aspect of which includes increased temperature in the tissues surrounding the inflammation site. In our study, we analyzed temperature-dependent neutrophil migration using differentiated HL-60 cells. The migration speed of differentiated HL-60 cells was found to correlate positively with temperature from 30 to 42 °C, with higher temperatures inducing a concomitant increase in cell detachment. The migration persistence time of differentiated HL-60 cells was higher at lower temperatures (30–33 °C), while the migration persistence length stayed constant throughout the temperature range. Coupled with the increased speed observed at high temperatures, this suggests that neutrophils are primed to migrate more effectively at the elevated temperatures characteristic of inflammation. Temperature gradients exist on both cell and tissue scales. Taking this into consideration, we also investigated the ability of differentiated HL-60 cells to sense and react to the presence of temperature gradients, a process known as thermotaxis. Using a two-dimensional temperature gradient chamber with a range of 27–43 °C, we observed a migration bias parallel to the gradient, resulting in both positive and negative thermotaxis. To better mimic the extracellular matrix (ECM) environment in vivo, a three-dimensional collagen temperature gradient chamber was constructed, allowing observation of biased neutrophil-like differentiated HL-60 migration toward the heat source.

Impact of Elevated CO2 and Temperature on Growth and Development of Helicoverpa armigera Hubner

Climate change is an imminent and inevitable circumstance largely driven by increase in CO2 and temperature. CO2 directly affects plants through positive effects on net photosynthetic rate. Higher temperature during the crop growth phase can diminish the yield, with a longer growing season. In the present study, adverse climate conditions i.e. elevated CO2 (550 ppm) and elevated temperatures (29, 31, 33 and 35 ± 1 °C) were simulated in carbon dioxide and temperature gradient chambers (CTG). Growth and development of Helicoverpa armigera on non-Bt and Bt cotton leaves from those CTG chambers were recorded and correlated with foliar carbohydrates and proteins.It was found that protein content decreased by almost 42 % in non-Bt cotton and by 36 % in Bt cotton, while larval weight and duration decreased significantly with elevated conditions particularly in Bt cotton. Relative Growth Rate (RGR) increased with eCO2+ eTemp and is relatively less in non-Bt cotton compared to Bt cotton by 4-13 mg g-1 day-1. Lower protein content is positively correlated significantly to larval growth rate (r = 0.9**). Effects of climate change on crops and their pests have to be further quantified precisely to develop plausible stress mitigation strategies.

Yield Response of Soybean [Glycine max (L.) Merrill] to High Temperature Condition in a Temperature Gradient Chamber

Yield Response of Soybean [Glycine max (L.) Merrill] to High Temperature Condition in a Temperature Gradient Chamber

Effects of elevated atmospheric CO2 concentration on growth and photosynthesis in eddo at two different air temperatures

ABSTRACT Future agricultural management programs should consider the responsiveness of crops to increasing atmospheric CO2 concentrations ([CO2]) and temperatures. Eddo is an important tuber crop widely grown in Asia, but its response to [CO2] and temperatures remains largely unknown. We investigated the responses of eddo and rice plants to elevated [CO2] (ambient [CO2] + 200 µmol mol−1) at low and high temperatures during the early-to-intermediate growth stage in temperature gradient chambers in 2018 and 2019. The dry weights (DWs) of the eddo leaf blades, petioles, roots, and above-ground parts as well as the DWs of the rice leaf blades, leaf sheaths and stems, above-ground parts, and whole plants significantly increased under elevated [CO2]. The number of leaves, leaf area, and SPAD value of eddo significantly increased under elevated [CO2], whereas the leaf area and SPAD value of rice did not. The net photosynthetic rate of eddo and rice tended to increase under elevated [CO2]. The increasing ratio of the total DW in elevated vs ambient [CO2] was significantly higher for eddo than for rice. The result indicates that elevated [CO2] increases the eddo biomass more than the rice biomass, possibly because of the increasing eddo leaf area and SPAD value induced by elevated [CO2]. The total DW of rice increased significantly in response to the high air temperature under elevated [CO2] conditions. However, the effect of [CO2] on the total DW of eddo was similar at both temperatures, reflecting the non-significant interaction between [CO2] and temperature. Abbreviations: [CO2]: atmospheric carbon dioxide concentration, DW: dry weight, FACE: free-air CO2 enrichment, g s: stomatal conductance, P N: net photosynthetic rate, TGC: temperature gradient chamber

The influence of high night temperature on yield and physiological attributes of Soybean cv. Fukuyutaka

ABSTRACT To evaluate soybean performance in response to high night temperature (HNT), a soybean cultivar, Fukuyutaka, was grown in 2 years under different night temperatures on a mini field in a temperature gradient chamber (TGC) at Kyoto, Japan. The average night temperature ranged from 21.7°C to 23.9°C and from 20.3°C to 22.8°C in 2017 and 2018, respectively. An additional experiment was conducted using a phytotron observing the same cv. under NT as high as 28°C (extreme HNT) and the control at 22 C from a R1 to R6.5 period. In the TGC yield tended to decline by 4.6% per °C when the results from the 2 years were combined. The responses of yield components tended to offset and the harvest index did not respond to varying NT. And thus the decrease in yield by HNT resulted from the change in biomass. The reduction of biomass was attributable more to branch growth than to main stem and more to leaf growth thant to other organs. Leaf area and leaf weight showed responses to NT as convex curves, suggesting that HNT may inhibit leaf growth. Reduction of biomass was more evident by extreme HNT in the phytotron. Pn was not significantly affected by HNT in TGC. The estimated maintenance respiration (Rm) increased with HNT but it seemed to explain the biomass response to HNT only partially. The results suggested that the growth and yield of soybean are potentially affected by increased NT through a negative impact on biomass production caused by multiple factors.

The Increase in the Arsenic Concentration in Brown Rice Due to High Temperature during the Ripening Period and Its Reduction by Silicate Material Treatment

We investigated the effect of temperature during the ripening period on the rice yield and arsenic (As) concentration in brown rice, using temperature gradient chambers (TGCs). Rice grown in Wagner pots (1/5000a) was placed in three TGCs (each TGC was set at four temperature levels: ambient, mildly-high temperature, moderately-high temperature, and super-high temperature) from one week after heading until harvest. In the TGCs, a range of mean air temperatures was observed in the range of 2 °C above the ambient temperature. There was a significant negative correlation between the brown rice yield and the air and soil temperatures, and the increase in air and soil temperatures resulted in a decrease in the yield. The reduction in yield was significantly mitigated by the application of calcium silicate. The concentration of As in the brown rice was significantly positively correlated with the air and soil temperature, and the concentration of As increased with increasing air and soil temperatures. When calcium silicate was applied, the concentration of As in brown rice was significantly lower at all temperature ranges, and its application was effective in reducing the arsenic concentration even at high temperatures. These results suggest that the application of silicate material may help mitigate the decrease in yield and the increasing As concentration in brown rice even under high-temperature conditions.

Phenotypic Plasticity Conditions the Response of Soybean Seed Yield to Elevated Atmospheric CO2 Concentration.

Selection for cultivars with superior responsiveness to elevated atmospheric CO2 concentrations (eCO2) is a powerful option for boosting crop productivity under future eCO2. However, neither criteria for eCO2 responsiveness nor prescreening methods have been established. The purpose of this study was to identify traits responsible for eCO2 responsiveness of soybean (Glycine max). We grew 12 Japanese and U.S. soybean cultivars that differed in their maturity group and determinacy under ambient CO2 and eCO2 for 2 years in temperature gradient chambers. CO2 elevation significantly increased seed yield per plant, and the magnitude varied widely among the cultivars (from 0% to 62%). The yield increase was best explained by increased aboveground biomass and pod number per plant. These results suggest that the plasticity of pod production under eCO2 results from biomass enhancement, and would therefore be a key factor in the yield response to eCO2, a resource-rich environment. To test this hypothesis, we grew the same cultivars at low planting density, a resource-rich environment that improved the light and nutrient supplies by minimizing competition. Low planting density significantly increased seed yield per plant, and the magnitude ranged from 5% to 105% among the cultivars owing to increased biomass and pod number per plant. The yield increase due to low-density planting was significantly positively correlated with the eCO2 response in both years. These results confirm our hypothesis and suggest that high plasticity of biomass and pod production at a low planting density reveals suitable parameters for breeding to maximize soybean yield under eCO2.

Genotypic differences in soybean yield responses to increasing temperature in a cool climate are related to maturity group

To adapt soybean production to climate change, a thorough understanding of its response to high temperature is required. Modeling studies have predicted that high temperature would shorten the growth period and hence lower seed yield of less day length-sensitive (early-maturing) soybean cultivars, whereas the magnitude of yield reduction by high temperature would be smaller in cultivars with higher day length sensitivity (late-maturing), suggesting that late-maturing cultivars would benefit from a future high-temperature environment. Current mean growing season temperature ranges from 19.4 to 22.6°C in the northern, cool regions of Japan, which is near or below the reported optimum temperature (22–24°C) for seed yield. We tested the hypothesis that adaptation by growing late-maturing cultivars will be successful in maintaining seed yield under a cool climate when temperature is increased during 21st century. We used three Japanese soybean cultivars, early-maturing Yukihomare and late-maturing cultivars Ryuhou and Enrei. Plants were grown over 3 years from June to September (a conventional season) under three temperature regimes, T1 (ambient), T2 (1.8–3.6°C above ambient), T3 (4.8–5.7°C above ambient), in a sunlit temperature gradient chamber. The leaf area at the full expansion stage, pod and seed numbers, and seed yield increased at elevated temperature in the late-maturing cultivars but not in the early-maturing one. The photosynthetic rate and effective quantum yield of photosystem II at the flowering stage increased at elevated temperature in all three cultivars. The period from sowing to the beginning of flowering (R1) decreased in all three cultivars at elevated temperature, whereas the period from R1 to the beginning of pod addition and the flowering period were prolonged in the late-maturing cultivars, but not in the early-maturing one. The differential response in post-flowering development in different maturity groups is probably related to the differences in the day length requirements of these cultivars. Our data clearly demonstrate that yield enhancement by increasing temperature in the late-maturing cultivars resulted from both the improvement in sources (leaf area and leaf photosynthesis) and the increase in sink size (number of flowers, pods and seeds) due to the longer flowering period. We conclude that the yield of the late-maturing cultivars sown during the conventional season in the cool regions of Japan will increase during the 21st century.

Planting geometry as a pre‐screening technique for identifying CO2 responsive rice genotypes: a case study of panicle number

Identifying CO(2) responsive genotypes is a major target for enhancing crop productivity under future global elevated atmospheric CO(2) concentration ([CO(2)]). However, [CO(2)]-fumigation facilities are extremely expensive and are not easily accessible, and are limited in space for large-scale screening. Hence, reliable donors for initiating [CO(2)]-responsive breeding programs are not in place for crops, including rice. We propose a simple and novel phenotyping method for identifying [CO(2)]-responsive genotypes, and quantify the responsiveness to low planting density over 4-year trials across both temperate and tropical conditions. Panicle number per plant is the key determinant of grain yield and hence was the focus trait across all our trials. In temperate climate, a 3-season field screening using 127 diverse rice genotypes and employing two planting densities (normal and low density) was conducted. Two japonica genotypes were selected based on their higher responsiveness to low planting density as candidates for validating the proposed phenotyping protocol as a pre-screen for [CO(2)]-responsiveness. The approach using the two selected candidates and three standard genotypes was confirmed using a free-air CO(2) enrichment facility and temperature gradient chambers under elevated [CO(2)]. In tropical climate, we grew three rice cultivars, previously identified for their [CO(2)]-responsiveness, at two planting densities. The experiments provided confirmation that responsiveness to low planting density was correlated with that of [CO(2)]-responsiveness across both the temperate and tropical conditions. The planting density would be useful pre-screening method for testing large panels of diverse germplasm at low cost complemented by available CO(2) -control facilities for final validation of candidates from the pre-screens.

The effects of increased temperature on crop growth and yield of soybean grown in a temperature gradient chamber

The global surface temperature is projected to rise and will affect crop performances. This study investigated the effects of increased temperature on yield and dry matter production in a controlled environment that mimicked field conditions using a temperature gradient chamber (TGC). Experiments were conducted from 2009 to 2012 using the soybean cultivar Enrei, which was grown in soil culture beds. Plants were grown in two TGCs as replicates for temperature treatment. Three temperature treatments, near ambient temperature (Ta), ambient temperature+1°C (Ta+1), and ambient temperature+3°C, in 2009 and 2010, and ambient temperature+2°C, in 2011 and 2012 (Ta+2/Ta+3), were established by dividing the rows along which the temperature gradient was created. The aboveground dry matter was significantly reduced by increased temperature from 11% in 2012 to 27% in 2009. Decrease of dry matter accumulation was obvious particularly from flowering to early seed filling and it was associated with decline of leaf photosynthetic rate, stomatal conductance and the carbon isotope discrimination. Reduced pod number, reduced seed number, and, to some extent, smaller seeds led to a decreased harvest index (HI). These phenomena might be associated with the delayed pod set and lower seed growth rate under warmer treatment. Seed yield was the most responsive parameter in 2009 and 2010, and in 2011 and 2012, it was still reduced under continuously wet conditions. Combined data showed that total dry matter, seed yield, and HI were consistently reduced by increased temperature. It is suggested that the concomitant increase of vapor pressure deficit with increased temperature exacerbated the temperature effects. In addition, reduced ambient CO2 and low light intensity as the artifacts of the facility might have accounted for the greater effect of high temperature.

Effects of Increasing Temperatures on Spikelet Fertility in Different Rice Cultivars based on Temperature Gradient Chamber Experiments

AbstractSpikelet sterility in rice (Oryza sativa L.) induced by high temperatures is a major concern given global warming predictions. We studied differences among eight rice cultivars in spikelet fertility at five different temperature levels in temperature gradient chamber (TGC) experiments. Six japonica and two indica cultivars were exposed to high‐temperature gradients in TGCs during the 2005 flowering season. Spikelet sterility increased with temperature in TGCs and differed among cultivars because of both variations in temperature tolerance and timing of heading. The correlation between spikelet fertility of individual panicles and both air temperature and panicle temperature during flowering was analyzed to compare tolerances among cultivars. The temperature (T75) at which spikelet fertility was 75 % of maximum ranged from 34 to 39 °C air temperature and differed significantly among cultivars. Indica varieties had higher T75 values than japonica varieties. The T75 values based on panicle temperature also differed among cultivars, but the difference between indica and japonica varieties were less significant. We concluded that the higher temperature tolerances of indica cultivars in our experiments could be attributed to lower spikelet temperatures, and cultivars with similar spikelet temperatures still had different heat tolerances due to differences in pollination ability.

Soybean yield and dry matter production as affected by increased temperature under near-field conditions in a temperature gradient chamber

Soybean yield and dry matter production as affected by increased temperature under near-field conditions in a temperature gradient chamber

Fertilizer N uptake of paddy rice in two soils with different fertility under experimental warming with elevated CO2

Only limited information is available in the research area on the effect of elevated CO2 concentration ([CO2]) and air temperature (Tair) on the fertilizer N uptake by rice. This study was conducted to investigate changes in rice uptake of N derived from fertilizer (NDFF) and soil (NDFS) as well as fertilizer N uptake efficiency (FUE) with elevated [CO2] and Tair in two soils with different fertility. Rice (Oryza sativa L.) plants were grown with 15N-urea for two growing seasons (2007 in the less fertile and 2008 in the more fertile soil) in temperature gradient chambers under two (ambient and elevated) levels of [CO2] and Tair regimes. At harvest, dry matter (DM) and N uptake amount of rice compartments (root, shoot, and grain) were determined. The DM of whole rice increased (P < 0.01) with co-elevation of [CO2] and Tair in both years (by 28.0 % in 2007 and by 27.4 % in 2008). The DM in 2008 was greater than that in 2007 by 48.1 to 63.1 % probably due to better soil fertility as well as longer sunshine hours (456 h vs. 568 h). Co-elevation of [CO2] and Tair increased total N uptake, NDFF, and NDFS by 19.4 to 29.1 % in general compared to the ambient conditions. The FUE increased with co-elevation of [CO2] and Tair from 46.5 to 59.5 % in 2007 and from 36.7 to 43.8 % in 2008. The projected global warming with elevated [CO2] is expected to increase FUE via enhanced DM accumulation with less increments in the soils that have higher indigenous soil N availabilities.

The response of soybean seed growth characteristics to increased temperature under near-field conditions in a temperature gradient chamber

Global warming and increasing soybean production in warm regions require a quantitative understanding of how yield-formation processes of this crop are affected by high temperatures. The response of soybean growth to increased temperature was examined under a controlled environment that mimics field conditions using a temperature gradient chamber (TGC). In 2009 and 2010, the (cv) Enrei cultivar was grown in soil culture beds (1m×24m) in two TGCs. Three temperature treatments, Ta (near ambient temperature), Ta+1 (ambient temperature +1°C) and Ta+3 (ambient temperature +3°C), were established by dividing the rows along which the temperature gradient was created. In 2009, only cvs. Ryuho and Suzuyutaka were grown under two temperature regimes. The mean temperatures in 2009 and 2010 for the entire growth period ranged from 25.9 to 28.7°C and from 27.1 to 30.1°C for Ta and Ta+3, respectively. The individual seed growth rate (SGR) was determined as the linear coefficient of the single-seed weight vs. time (d), based on periodic plant harvesting. The effective seed-filling period (EFP) was calculated by dividing the final single-seed weight by the SGR. The flowering date was affected by increased temperature only in 2010. The days to beginning of seed fill and maturity were longer under higher temperatures. The SGR was slower at Ta+3 (7.1 and 5.9mg seed−1d−1 in 2009 and 2010, respectively) than at Ta (8.5 and 7.5mg seed−1 d−1 in 2009 and 2010, respectively), whereas the EFP was longer under high temperatures than at near ambient temperature. The final single-seed weight was reduced by increased temperatures. The temperature had no significant effect on cell volume, but the number of cells per cotyledon was smaller at Ta+3 (3.4×106 and 2.6×106 in 2009 and 2010, respectively) than at Ta (5.0×106 and 4.3×106). The results indicated that an increase in temperature by 3°C in warm regions decreased the seed size of soybean by decreasing the cell number and SGR.

Effects of elevated CO2 concentration and temperature on seed production and nitrogen concentration in soybean (Glycine max (L.) Merr.)

The effects of elevated carbon dioxide concentration ([CO2]) and temperature and their interactions on leaf photosynthesis, reproductive processes, seed weight and seed nitrogen concentration ([N]) of soybeans (Glycine max (L.) Merr.) were investigated using temperature gradient chambers. Plants were grown under four regimes comprising two levels of [CO2], ambient (LC) and ambient +200 μmol mol-1 (HC), and two levels of temperature, low (LT) and high (HT, LT +∼3°C). Plant and seed weights were significantly increased by elevated [CO2] in both temperature regimes. Increased seed weight under elevated [CO2] was mainly because of the production of more nodes and seeds per plant. Increased temperature significantly increased the number of seeds per plant but decreased individual seed weight in both [CO2] regimes. Increased temperature therefore had no effect on seed weight. The increased seed number per plant in the HT regimes resulted from increased pod numbers per node. The light-saturated photosynthetic rate increased with increasing [CO2] and temperature, presumably resulting in more seeds per plant. The reduction in individual seed weight with increased temperature was attributed mainly to lower individual seed growth rate and fewer cotyledon cells per seed. The reduction in individual seed weight with increased temperature was less pronounced in the HC regime than in the LC regime, and there was a significant interaction between [CO2] and temperature. However, there was no interaction between [CO2] and temperature for seed weight. Neither individual effects nor interaction of [CO2] and temperature were observed for seed [N]. This study raises the possibility that projected increases in atmospheric [CO2] during the 21st century will increase the yield of soybeans without decreasing seed [N] in regions that have near or below optimum temperatures (near 25°C or above) for soybean yield.

Down-regulation of Rubisco activity under combined increases of CO2 and temperature minimized by changes in Rubisco kcat in wheat

Increases in growth temperature have been observed to affect photosynthesis differently under long-term exposure to ambient- and twice ambient-air CO2 concentrations. This study investigates the causes of this interaction in wheat (Triticum aestivum L.) grown in the field over two consecutive years under temperature gradient chambers in ambient (370 μmol mol−1) or elevated (700 μmol mol−1) atmospheric CO2 concentrations and at ambient or ambient +4°C temperatures, with either a low or a high nitrogen supply. The photosynthesis-internal CO2 response curves and the activity, activation state, kcat and amount of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were measured, as well as the soluble protein concentration in flag leaves at ear emergence and 8–15 days after anthesis. A high nitrogen supply increased Vcmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco kcat. Both elevated CO2 and above ambient temperatures had negative effects on Vcmax and Rubisco activity, but at elevated CO2, an increase in temperature did not decrease Vcmax or Rubisco activity in relation to ambient temperature. The amounts of Rubisco and soluble protein decreased with elevated CO2 and temperature. The negative impact of elevated CO2 on Rubisco properties was somewhat counteracted at elevated temperatures by an increase in kcat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO2 and temperature.

Is yield enhancement by CO 2 enrichment greater in genotypes with a higher capacity for nitrogen fixation?

Yield responsiveness to elevated CO 2 concentration [CO 2] was previously found to be greater when nitrogen (N) was supplied in adequate amounts; however, it remains unclear whether genotypic differences in N 2-fixing capacity affect yield responsiveness in soybean. We tested the hypothesis that yield responsiveness to elevated [CO 2] in soybean is greater in a genotype with a higher capacity for N 2 fixation. We used three near-isogenic genotypes with contrasting nodulation capacities: super-nodulating, normally nodulating and non-nodulating genotypes. Plants were subjected to two levels of [CO 2] (ambient or elevated: ambient + 200 μmol mol −1) and two temperature regimes (low or high: low + ca. 4–5 °C) using temperature gradient chambers. The super-nodulating genotype exhibited a higher N content in leaves, regardless of [CO 2] and temperature. Photosynthetic rates were enhanced by CO 2 enrichment at earlier growth stages, but not at later growth stages, regardless of genotype. This photosynthetic acclimation was reflected in biomass production in all the genotypes examined. Yield responsiveness to elevated [CO 2] was greater in the nodulating genotypes than in the non-nodulating genotype, but the genotypic differences were obscured between the normally nodulating and super-nodulating genotype, thus our hypothesis was not fully verified.