Acclimation of peanut (Arachis hypogaea L.) leaf photosynthesis to elevated growth CO2 and temperature

Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO₂ concentrations ([CO₂]) of 360 μmol mol⁻¹ (ambient) and 720 μmol mol⁻¹ (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO₂] and temperature, and to assess whether elevated [CO₂] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO₂] had higher midday photosynthetic CO₂ exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO₂]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO₂]. Declines in Rubisco under elevated growth [CO₂] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO₂], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO₂] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO₂] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO₂] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO₂]. Under elevated [CO₂], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO₂] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO₂]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO₂] and temperature as predicted for this century.     

Elevated CO2 and water-availability effect on gas exchange and nodule development in N2-fixing alfalfa plants

N₂-fixing alfalfa plants were grown in controlled conditions at different CO₂ levels (350 μmol mol^?1 versus 700 μmol mol^?1) and water-availability conditions (WW, watered at maximum pot water capacity versus WD, watered at 50% of control treatments) in order to determine the CO₂ effect (and applied at two water regimes) on plant growth and nodule activity in alfalfa plants. The CO₂ stimulatory effect (26% enhancement) on plant growth was limited to WW plants, whereas no CO₂ effect was observed in WD plants. Exposure to elevated CO₂ decreased Rubisco carboxylation capacity of plants, caused by a specific reduction in Rubisco (EC 4.1.1.39) concentration (11% in WW and 43% in WD) probably explained by an increase in the leaf carbohydrate levels. Plants grown at 700 μmol mol^?1 CO₂ maintained control photosynthetic rates (at growth conditions) by diminishing Rubisco content and by increasing nitrogen use efficiency. Interestingly, our data also suggest that reduction in shoot N demand (reflected by the TSP and especially Rubisco depletion) affected negatively nodule activity (malate dehydrogenase, EC 1.1.1.37, and glutamate-oxaloacetate transaminase, EC 2.6.1.1, activities) particularly in water-limited conditions. Furthermore, nodule DM and TSS data revealed that those nodules were not capable to overcome C sink strength limitations.     

Gas exchange acclimation to elevated CO2 in upper-sunlit and lower-shaded canopy leaves in relation to nitrogen acquisition and partitioning in wheat grown in field chambers

Growth at elevated CO₂ often decreases photosynthetic capacity (acclimation) and leaf N concentrations. Lower-shaded canopy leaves may undergo both CO₂ and shade acclimation. The relationship of acclimatory responses of flag and lower-shaded canopy leaves of wheat (Triticum aestivum L.) to the N content, and possible factors affecting N gain and distribution within the plant were investigated in a wheat crop growing in field chambers set at ambient (360 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂, and with two amounts of N fertilizer (none and 70 kg ha⁻¹ applied on 30 April). Photosynthesis, stomatal conductance and transpiration at a common measurement CO₂, chlorophyll and Rubisco levels of upper-sunlit (flag) and lower-shaded canopy leaves were significantly lower in elevated relative to ambient CO₂-grown plants. Both whole shoot N and leaf N per unit area decreased at elevated CO₂, and leaf N declined with canopy position. Acclimatory responses to elevated CO₂ were enhanced in N-deficient plants. With N supply, the acclimatory responses were less pronounced in lower canopy leaves relative to the flag leaf. Additional N did not increase the fraction of shoot N allocated to the flag and penultimate leaves. The decrease in photosynthetic capacity in both upper-sunlit and lower-shaded leaves in elevated CO₂ was associated with a decrease in N contents in above-ground organs and with lower N partitioning to leaves. A single relationship of N per unit leaf area to the transpiration rate accounted for a significant fraction of the variation among sun-lit and shaded leaves, growth CO₂ level and N supply. We conclude that reduced stomatal conductance and transpiration can decrease plant N, leading to acclimation to CO₂ enrichment.     

Down-regulation of Rubisco activity under combined increases of CO<Subscript>2</Subscript> and temperature minimized by changes in Rubisco k<Subscript>cat</Subscript> 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, k_cat 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 V_cmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco k_cat. Both elevated CO₂ and above ambient temperatures had negative effects on V_cmax and Rubisco activity, but at elevated CO₂, an increase in temperature did not decrease V_cmax 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 k_cat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO₂ and temperature.     

Impact of in vitro CO2 enrichment and sugar deprivation on acclimatory responses of Phalaenopsis plantlets to ex vitro conditions

We assessed the effect of growth at either 400 μmol mol^?1 (ambient) or 1000 μmol mol^?1 (elevated) CO₂ and 0 g L^?1 (deprivation) or 30 g L^?1 (supplementation) sugar on morphological traits, photosynthetic attributes and intrinsic elements of the CAM pathway using the CAM orchid Phalaenopsis ‘Amaglade’. The growth of shoot (retarded) and root (induced) was differently affected by CO₂ enrichment and mixotrophic regime (+sugar). The Fv/Fm ratio was 14% more in CO₂-enriched treatment than at ambient level during in vitro growth. At elevated level of CO₂ and sugar treatment, the content of Chl(a + b), Chl a/b and Chl/Car was enhanced while carotenoid content remained unaltered. During in vitro growth, gas-exchange analysis indicated that increased uptake of CO₂ accorded with the increased rate of transpiration and unchanged stomatal conductance at elevated level of CO₂ under both photo- and mixotrophic growth condition. At elevated level of CO₂ and sugar deprivation, activities of Rubisco (26.4%) and PEPC (74.5%) was up-regulated. Among metabolites, the content of sucrose and starch was always higher under CO₂ enrichment during both in vitro and ex vitro growth. Our results indicate that plantlets grown under CO₂ enrichment developed completely viable photosynthetic apparatus ready to be efficiently transferred to ex vitro condition that has far-reaching implications in micropropagation of Phalaenopsis.     

Climate change,nutrition and immunity: Effects of elevated CO2 and temperature on the immune function of an insect herbivore

Balanced nutrition is fundamental to health and immunity. For herbivorous insects, nutrient-compositional shifts in host plants due to elevated atmospheric CO₂ concentrations and temperature may compromise this balance. Therefore, understanding their immune responses to such shifts is vital if we are to predict the outcomes of climate change for plant–herbivore–parasitoid and pathogen interactions. We tested the immune response of Paropsis atomaria Olivier (Coleoptera: Chrysomelidae) feeding on Eucalyptus tereticornis Sm. seedlings exposed to elevated CO₂ (640 μmol mol⁻¹; C_E) and temperature (ambient plus 4 °C; T_E). Larvae were immune-challenged with a nylon monofilament in order to simulate parasitoid or pathogen attack without other effects of actual parasitism or pathology. The cellular (in vivo melanisation) and humoral (in vitro phenoloxidase PO activity) immune responses were assessed, and linked to changes in leaf chemistry. C_E reduced foliar nitrogen (N) concentrations and increased C:N ratios and concentrations of total phenolics. The humoral response was reduced at C_E. PO activity and haemolymph protein concentrations decreased at C_E, while haemolymph protein concentrations were positively correlated with foliar N concentrations. However, the cellular response increased at C_E and this was not correlated with any foliar traits. Immune parameters were not impacted by T_E. Our study revealed that opposite cellular and humoral immune responses occurred as a result of plant-mediated effects at C_E. In contrast, elevated temperatures within the tested range had minimal impact on immune responses. These complex interactions may alter the outcomes of parasitoid and pathogen attack in future climates.     

Growth and development of cotton (Gossypium hirsutum L.) in response to CO2 enrichment under two different temperature regimes

An increase in atmospheric CO₂ concentration ([CO₂]) together with other climate change factors could greatly affect agricultural productivity. Understanding the impact of the change in atmospheric [CO₂] in conjunction with the ongoing global change is crucial to prepare for mitigation and any adaptation for future agricultural production. The main goal of this project was to study the time-course pattern of cotton plant growth in response to [CO₂] and temperature to investigate the hypothesis that whether response to elevated [CO₂] would change at different temperatures. An experiment was conducted in the controlled-environment chambers of the Georgia Envirotron with two different day/night temperatures levels, e.g., 25/15 °C and 35/25 °C, and three CO₂ concentrations, e.g., 400, 600 and 800 μmol l^?1. The experimental design was completely randomized with four replicates (plastic containers) per treatment. Growth analysis was conducted at bi-weekly intervals during the growing season. In addition, leaf area, leaf dry mass, root dry mass, square dry mass, boll dry mass and total above dry mass per plant were also measured at each sampling. Plant traits, including plant height, number of leaves, number of squares and number of bolls were recorded weekly. The number of days to emergence, squaring, flowering and maturity were also observed. The results showed that by increasing [CO₂] to 600 μmol l^?1 total biomass increased at both temperature levels, but a further increase of [CO₂] up to 800 μmol l^?1 increased total biomass only at the temperature of 35/25 °C. Throughout the growing season, there was no significant effect of [CO₂] levels on LAI. Increasing temperature from 25/15 °C to 35/25 °C had a positive impact on LAI across all CO₂ levels (P < 0.05). Increasing CO₂ from 400 to 600 μmol l^?1 significantly increased the number of squares by 31.4%, but a further increase to 800 μmol l^?1 caused a 6.6% decrease (non-significant) in the number of squares. The interactive effects of [CO₂] and temperature indicated that at a higher temperature, CO₂ would be more beneficial as we proceed towards the end of the growing season. However, further studies are needed to really understand the interaction between higher [CO₂] and temperature levels and cultivar characteristics.     

Interactive effects of elevated temperature and CO2 levels on metabolism and oxidative stress in two common marine bivalves (Crassostrea virginica and Mercenaria mercenaria)

Marine bivalves such as the hard shell clams Mercenaria mercenaria and eastern oysters Crassostrea virginica are affected by multiple stressors, including fluctuations in temperature and CO₂ levels in estuaries, and these stresses are expected to be exacerbated by ongoing global climate change. Hypercapnia (elevated CO₂ levels) and temperature stress can affect survival, growth and development of marine bivalves, but the cellular mechanisms of these effects are not yet fully understood. In this study, we investigated whether oxidative stress is implicated in cellular responses to elevated temperature and CO₂ levels in marine bivalves. We measured the whole-organism standard metabolic rate (SMR), total antioxidant capacity (TAOC), and levels of oxidative stress biomarkers in the muscle tissues of clams and oysters exposed to different temperatures (22 and 27 °C) and CO₂ levels (the present day conditions of ~ 400 ppm CO₂ and 800 ppm CO₂ predicted by a consensus business-as-usual IPCC emission scenario for the year 2100). SMR was significantly higher and the antioxidant capacity was lower in oysters than in clams. Aerobic metabolism was largely temperature-independent in these two species in the studied temperature range (22–27 °C). However, the combined exposure to elevated temperature and hypercapnia led to elevated SMR in clams indicating elevated costs of basal maintenance. No persistent oxidative stress signal (measured by the levels of protein carbonyls, and protein conjugates with malondialdehyde and 4-hydroxynonenal) was observed during the long-term exposure to moderate warming (+ 5 °C) and hypercapnia (~ 800 ppm CO₂). This indicates that long-term exposure to moderately elevated CO₂ and temperature minimally affects the cellular redox status in these bivalve species and that the earlier observed negative physiological effects of elevated CO₂ and temperature must be explained by other cellular mechanisms.     

Involvement of nitrogen and cytokinins in photosynthetic acclimation to elevated CO2 of spring wheat

Acclimation of photosynthetic capacity to elevated CO₂ involves a decrease of the leaf Rubisco content. In the present study, it was hypothesized that nitrogen uptake and partitioning within the leaf and among different aboveground organs affects the down-regulation of Rubisco. Given the interdependence of nitrogen and cytokinin signals at the whole plant level, it is also proposed that cytokinins affect the nitrogen economy of plants under elevated CO₂, and therefore the acclimatory responses. Spring wheat received varying levels of nitrogen and cytokinin in field chambers with ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂. Gas exchange, Rubisco, soluble protein and nitrogen contents were determined in the top three leaves in the canopy, together with total nitrogen contents per shoot. Growth in elevated CO₂ induced decreases in photosynthetic capacity only when nitrogen supply was low. However, the leaf contents of Rubisco, soluble protein and total nitrogen on an area basis declined in elevated CO₂ regardless of nitrogen supply. Total nitrogen in the shoot was no lower in elevated than ambient CO₂, but the fraction of this nitrogen located in flag and penultimate leaves was lower in elevated CO₂. Decreased Rubisco: chlorophyll ratios accompanied losses of leaf Rubisco with CO₂ enrichment. Cytokinin applications increased nitrogen content in all leaves and nitrogen allocation to senescing leaves, but decreased Rubisco contents in flag leaves at anthesis and in all leaves 20 days later, together with the amount of Rubisco relative to soluble protein in all leaves at both growth stages. The results suggest that down regulation of Rubisco in leaves at elevated CO₂ is linked with decreased allocation of nitrogen to the younger leaves and that cytokinins cause a fractional decrease of Rubisco and therefore do not alleviate acclimation to elevated CO₂.     

Pea plant responsiveness under elevated [CO2] is conditioned by the N source (N2 fixation versus NO3− fertilization)

The main goal of this study was to test the effect of [CO₂] on C and N management in different plant organs (shoots, roots and nodules) and its implication in the responsiveness of exclusively N₂-fixing and NO₃⁻-fed plants. For this purpose, exclusively N₂-fixing and NO₃⁻-fed (10 mM) pea (Pisum sativum L.) plants were exposed to elevated [CO₂] (1000 μmol mol⁻¹ versus 360 μmol mol⁻¹ CO₂). Gas exchange analyses, together with carbohydrate, nitrogen, total soluble proteins and amino acids were determined in leaves, roots and nodules. The data obtained revealed that although exposure to elevated [CO₂] increased total dry mass (DM) in both N treatments, photosynthetic activity was down-regulated in NO₃⁻-fed plants, whereas N₂-fixing plants were capable of maintaining enhanced photosynthetic rates under elevated [CO₂]. In the case of N₂-fixing plants, the enhanced C sink strength of nodules enabled the avoidance of harmful leaf carbohydrate build up. On the other hand, in NO₃⁻-fed plants, elevated [CO₂] caused a large increase in sucrose and starch. The increase in root DM did not contribute to stimulation of C sinks in these plants. Although N₂ fixation matched plant N requirements with the consequent increase in photosynthetic rates, in NO₃⁻-fed plants, exposure to elevated [CO₂] negatively affected N assimilation with the consequent photosynthetic down-regulation.     

Effects of gradual versus step increases in carbon dioxide on Plantago photosynthesis and growth in a microcosm study

This study investigated the effects of a gradual versus step increases in carbon dioxide (CO₂) on plant photosynthesis and growth at two nitrogen (N) levels. Plantago lanceolata were grown for 80 days and then treated with the ambient CO₂ (as the control), gradual CO₂ increase and step CO₂ increase as well as low and high N additions for 70 days. While [CO₂] were kept at constant 350 and 700 μmol mol⁻¹ for the ambient and step CO₂ treatments, respectively, [CO₂] in the gradual CO₂ treatment was raised by 5 μmol mol⁻¹ day⁻¹, beginning at 350 μmol mol⁻¹ and reaching 700 μmol mol⁻¹ by the end of experiment. The step CO₂ treatment immediately resulted in an approximate 50% increase in leaf photosynthetic carbon fixation at both the low and high N additions, leading to a 20–24% decrease in leaf N concentration. The CO₂-induced nitrogen stress, in return, resulted in partial photosynthetic downregulation since the third week at the low N level and the fourth week at the high N level after treatments. In comparison, the gradual CO₂ treatment induced a gradual increase in photosynthetic carbon fixation, leading to less reduction in leaf N concentration. In comparison to the ambient CO₂, both the gradual and step CO₂ increases resulted in decreases in specific leaf area, leaf N concentration but an increase in plant biomass. Responses of plant shoot:root ratio to CO₂ treatments varied with N supply. It decreased with low N supply and increased with high N supply under the gradual and step CO₂ treatments relative to that under the ambient CO₂. Degrees of those changes in physiological and growth parameters were usually larger under the step than the gradual CO₂ treatments, largely due to different photosynthetic C influxes under the two CO₂ treatments.     

Exposures to elevated CO2, elevated temperature and enhanced UV-B radiation modify activities of polyphenol oxidase and guaiacol peroxidase and concentrations of chlorophylls,polyamines and soluble proteins in the leaves of Betula pendula seedlings

The activity of polyphenol oxidase (PPO) and guaiacol peroxidase (POD) and the concentrations of chlorophylls, free polyamines and soluble proteins were determined from the leaves of six genotypes of silver birch (Betula pendula Roth) seedlings exposed to short-term elevated carbon dioxide (CO₂), temperature (T), ultraviolet-B irradiation (UV-B, 280-315 nm) and their combinations. Results showed that the activity of PPO in the leaves was low but increased by elevated CO₂ and elevated T. The POD activity varied between the genotypes due to an interactive effect of CO₂ × UV-B. The soluble proteins were clearly decreased by elevated CO₂, but the level of response varied among the genotypes. The concentrations of chl a and total chlorophylls were lower in the leaves treated with elevated CO₂ than in leaves grown at ambient CO₂. An interactive effect of CO₂ × UV-B on the chl a/b ratio was found. Elevated T increased chl b concentration and decreased chl a/b ratio. Temperature treatments also caused variation in the concentrations of chl a, chl b and total chlorophylls among the genotypes. Polyamine analyses showed that the concentrations of putrescine were increased and spermine decreased in leaves treated with elevated T. However, the change in putrescine by elevated T was clearer at ambient CO₂ than in eCO₂ environment (significant effect of T × CO₂). In conclusion, the defensive enzymes, photosynthetic pigments, soluble proteins and growth-regulating polyamines in silver birch leaves were not susceptible to enhanced UV-B radiation. In contrast, all the variables responded to elevated T and/or elevated CO₂, reflecting the enhancive effects of climate change conditions not only on leaf productivity, but also on leaf turn-over rate. Most of these climate-driven changes were not regulated by UV-B radiation.     

Response of nodulated alfalfa to water supply,temperature and elevated CO2: productivity and water relations

Exposing plants to long-term CO₂ enrichment generally leads to increases in plant biomass, total leaf area and alterations on leaf net photosynthetic rates, stomatal conductance and water use efficiency. However, the magnitude of such effects is dependent on the availability of other potentially limiting resources. The aim of our study was to elucidate the effects of elevated CO₂, applied at different temperature and water availability regimes, on nodulated alfalfa plants. Regardless of water supply, elevated CO₂ enhanced plant growth, especially when combined with increased temperature although no differences were detected until 30 days of treatment. Absence of differences in leaf relative growth rate, and gas exchange measurements, suggested that plants grown in a low water regime adjusted their growth to the amount of available water. Elevated CO₂ enhanced water use efficiency because of reduced water consumption and a greater dry mass production. Increased dry matter production of plants grown under elevated CO₂ and temperature was the result of stimulated photosynthetic rates, greater leaf area and water use efficiency. Lack of CO₂ effect on photosynthesis of plants grown at ambient temperature might be consequence of down-regulation phenomena. Plants grown at 700 μmol mol⁻¹ CO₂ maintained control nitrogen levels, discarding enhanced nitrogen availability as the main factor explaining enhanced dry matter.     

The mechanism(s) involved in the photoprotection of PSII at elevated CO2 in nodulated alfalfa plants

In a previous study, we found that enhanced CO₂ subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO₂ levels in this plant. Elevated CO₂ reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H₂O₂ and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol⁻¹ CO₂ compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO₂ induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.     

The mechanism(s) involved in the photoprotection of PSII at elevated CO2 in nodulated alfalfa plants

In a previous study, we found that enhanced CO₂ subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4 °C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO₂ levels in this plant. Elevated CO₂ reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H₂O₂ and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700 μmol mol^?1 CO₂ compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO₂ induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.     

Plasticity of rice tiller production is related to genotypic variation in the biomass response to elevated atmospheric CO2 concentration and low temperatures during vegetative growth

Appropriate resource partitioning to either production of new tillers or growth of individual tillers is a critical factor for increasing rice biomass production and facilitating adaptation to climate change. We examined the contributions of genotypic variation to the tiller number and individual tiller growth of 24 rice cultivars in response to an elevated atmospheric CO₂ concentration [CO₂] (control + 191 μmol mol⁻¹) and a low air temperature (control minus 4.7 °C) during 56 days of vegetative growth after transplanting. For all genotypes combined, biomass increased by 27% under elevated [CO₂] and decreased by 34% at low temperature, with a significant genotype × temperature interaction. The increase caused by elevated [CO₂] resulted from increased tiller number, and the decrease caused by low temperature resulted from decreased growth of individual tillers. Despite the different overall responses to elevated [CO₂] and low temperature, most of the genotypic variation in biomass at elevated [CO₂] and low temperature was explained by the responses of tiller number rather than by individual tiller growth. The genotypes with the highest biomass response to elevated [CO₂] had a smaller reduction of biomass under low temperature. These results highlight the greater importance of genotypic variation in tiller number than in individual tiller growth in the response of biomass to environmental change.     

Increased feeding damage under elevated Co2: The case of the Russian wheat aphid

We report the results of a baseline study on the effects of Russian wheat aphid infestation on barley lines grown under ambient and elevated (450 and 550 μmol mol^− 1) CO₂ concentrations [CO₂]. Elevated CO₂ impacted on plant biomass, C:N ratios and leaf nitrogen concentrations. Visible manifestation of aphid feeding related damage was assessed by examining resultant chlorosis and leaf roll under ambient and two elevated [CO₂] levels using a control and three resistant barley host combinations. Elevated [CO₂] had a significant positive effect on the growth of the four barley lines that were not infested by the aphids. However under the same conditions aphid feeding under elevated CO₂ conditions caused very high biomass loss, which was more noticeable in experiments involving non-resistant PUMA than in the resistant barley lines. The results of this study demonstrate that CO₂ enrichment substantially increases aphid populations of RWASA1 and RWASA2 on the four barley lines investigated. Furthermore, aphid populations were higher on non-resistant PUMA than the three resistant lines and the RWASA2 biotype out-performed RWASA1 in each case. Under elevated [CO₂], aphid feeding, resulted in a significant increase in the leaf C:N ratios (as a percentage change) in most treatments, compared to levels recorded on uninfested plants. The resistant lines also showed a significant reduction in leaf nitrogen (~ 40% for PUMA and not less than 30% for the resistant STARS lines tested). C:N ratio changes and N loss correlated to [CO₂] and aphid biotype. By 28 days of infestation, most of the non-resistant PUMA line in particular showed significant irrecoverable levels of leaf chlorosis. At level 9 rating on the chlorosis scale (i.e. plant death when recovery was not possible), experiments were terminated. As aphid success is unlikely to be the sole product of [CO₂], but also of other limiting nutrients such as N, it may be worth further investigating the effect of plant quality and ultimately plant nutrition on the population growth of aphids.     

Elevated atmospheric CO2 decreases oxidative stress and increases essential oil yield in leaves of Thymus vulgaris grown in a mini-FACE system

Potted one-year-old plants of Thymus vulgaris L. (thyme, Lamiaceae, C3 metabolism), were grown for three months (10 June–10 September, 2004) in a “mini-free-air-CO₂-enrichment” (“mini-FACE”) system, under 500 μmol mol^?1 and ambient concentrations of atmospheric carbon dioxide (CO₂). Compared to ambient CO₂, elevated CO₂ stimulated leaf superoxide dismutase (SOD, EC 1.15.1.1) activity only at the first sampling-time (July), followed by no variation or even a trend of decreased activity on the other two sampling-times (August and September). Under high CO₂, guaiacol peroxidase (GPX, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) leaf activities showed no variation or drop throughout the duration of the experiment. By contrast, under elevated CO₂, leaf glutathione reductase (GR, EC 1.6.4.2) activity increased on all the sampling-times, and also a duration-dependent upward trend of glutathione (GSH) content was recorded, with this increase becoming significant – compared with ambient CO₂ – at the third sampling-time (September). Simultaneously, leaves from plants grown under high CO₂ showed a marked increase in essential oil yield, with slight increments in phenolic component and decrements in mono- and sesquiterpene components. Also, a drop in thiobarbituric acid reactive substances (TBARS) content under elevated CO₂ was displayed. Thus, in general, the results reported here point to a downregulation of leaf antioxidant enzymes under elevated CO₂, supporting the notion of reduced reactive oxygen species (ROS) formation under these circumstances. Relying instead on antioxidant-regenerating enzymes, namely GR, fairly high GSH content and essential oils, might be a ‘low cost’ life strategy for growth under elevated CO₂, not requiring synthesis/activation of energy-intensive and expensive metabolic processes.     

Interacting effects of CO2 concentration, temperature and nitrogen supply on the photosynthesis and composition of winter wheat leaves

Winter wheat (Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO₂ concentrations (350 and 700 μmol mol⁻¹), two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4°C] and two rates of nitrogen supply (equivalent to 489 kg ha⁻¹ and 87 kg ha⁻¹). Leaves grown at 700 μmol mol⁻¹ CO₂ had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO₂ concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long-term exposure to elevated CO₂ concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO₂ concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO₂ concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity.     

Temperature dependence of growth,development, and photosynthesis in maize under elevated CO2

Global atmospheric carbon dioxide concentrations (C_a) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4–5.8 °C with the doubling of C_a by the end of the century. Because, changes in C_a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C_a in major crop plants including maize (Zea mays L.), a globally important grain crop with C₄ photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 °C under current (370 μmol mol⁻¹) and doubled (750 μmol mol⁻¹) C_a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C_a. Leaf and canopy photosynthetic rates, C₄ enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C_a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C_a was not changed in response to CO₂ enrichment. Carboxylation efficiency and the activities of C₄ enzymes were reduced with CO₂ enrichment indicating possible photosynthetic acclimation of the C₄ cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 °C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C₄ enzyme activities on growth temperatures was comparable between current and elevated C_a. The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C_a compared with current C_a in maize.