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C sink/source balance and N assimilation have been identified as target processes conditioning crop responsiveness to elevated CO2. However, little is known about phenology-driven modifications of C and N primary metabolism at elevated CO2 in cereals such as wheat. Here, we examined the differential effect of elevated CO2 at two development stages (onset of flowering, onset of grain filling) in durum wheat ( Triticum durum, var. Sula) using physiological measurements (photosynthesis, isotopes), metabolomics, proteomics and 15 N labelling. Our results show that growth at elevated CO2 was accompanied by photosynthetic acclimation through a lower internal (mesophyll) conductance but no significant effect on Rubisco content, maximal carboxylation or electron transfer. Growth at elevated CO2 altered photosynthate export and tended to accelerate leaf N remobilization, which was visible for several proteins and amino acids, as well as lysine degradation metabolism. However, grain biomass produced at elevated CO2 was larger and less N rich, suggesting that nitrogen use efficiency rather than photosynthesis is an important target for improvement, even in good CO2-responsive cultivars. [ABSTRACT FROM AUTHOR]

Although climate scenarios have predicted an increase in [CO2] and temperature conditions, to date few experiments have focused on the interaction of [CO2] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO2. The main goal of this study was to analyze the effect of interacting [CO2] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO2] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO2] (400 vs 700 µmol mol−1) and temperature (ambient vs ambient + 4°C) in CO2 gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO2] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO2] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO2] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity. [ABSTRACT FROM AUTHOR]

The natural 15N/14 N isotope composition (d N) of a tissue is a consequence of its N source and N physiological mechanisms in response to the environment. It could potentially be used as a tracer of N metabolism in plants under changing environmental conditions, where primary N metabolism may be complex, and losses and gains of N fluctuate over time. In order to test the utility of δ15N as an indicator of plant N status in N2-fixing plants grown under various environmental conditions, alfalfa (Medicago sativa L.) plants were subjected to distinct conditions of [CO2] (400 vs. 700µmol-1 mol-1), temperature (ambient vs. ambient 4°C) and water availability (fully watered vs. water deficiency--WD). As expected, increased [CO2] and temperature stimulated photosynthetic rates and plant growth, whereas these parameters were negatively affected by WD. The determination of δ15N in leaves, stems, roots, and nodules showed that leaves were the most representative organs of the plant response to increased [CO2] and WD. Depletion of heavier N isotopes in plants grown under higher [CO2] and WD conditions reflected decreased transpiration rates, but could also be related to a higher N demand in leaves, as suggested by the decreased leaf N and total soluble protein (TSP) contents detected at 700µmol mol-1 [CO2] and WD conditions. In summary, leaf δ15N provides relevant information integrating parameters which condition plant responsiveness (e.g., photosynthesis, TSP, N demand, and water transpiration) to environmental conditions. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 is a major contributor to the greenhouse effect and is one of the main inducers of climate change. Previous studies with nodulated alfalfa plants have shown that elevated CO2 increased the growth of plants grown under well-watered or limited water supply conditions. The beneficial effects of atmospheric CO2 enrichment included higher photosynthetic rates, growth and water-use efficiency and an increase in the root/shoot ratio. However, at the moment, we do not have information on the possible implications of the beneficial effect of elevated CO2 as it may relate to a higher capacity of the violaxanthin–antheraxanthin–zeaxanthin (VAZ) cycle, the dissipation of excess radiation as heat and the effect on photooxidation, and to an improved leaf antioxidant system (Halliwell–Asada cycle). The aim of the present study was to determine the effects of the interaction between CO2 (ambient, around 350 vs 700 μmol mol−1), temperature (ambient vs ambient + 4°C) and water availability (well irrigated vs partially irrigated) on the leaf antioxidant status of nodulated alfalfa during regrowth. Parameters measured in this study included relative growth rate (RGR), H2O2 content, oxidative damage [measured as thiobarbituric acid-reacting substances (TBARS)], leaf pigment composition (chlorophylls and xanthophylls), ascorbate (ASA) and glutathione pool levels and antioxidant enzymes. Our results revealed that during alfalfa regrowth, the effects of elevated CO2, limited water supply, temperature and their interactions on growth were not related to significant or general changes in leaf antioxidant capacity, H2O2 accumulation or oxidative stress (TBARS concentrations). The beneficial effects of CO2 enrichment in well-watered and limited water-subjected plants were not associated with an increase in the capacity of alfalfa leaves to dissipate excess radiation as heat through the VAZ cycle or with an increase in the antioxidant capacity, measured in terms of Halliwell–Asada cycle enzymes and antioxidant compounds. Furthermore, elevated CO2 did not affect RGRs during the last 15 days of regrowth and reduced the activity of several antioxidant enzymes (catalase, superoxide dismutase and glutathione reductase and ASA peroxidase in limited water-subjected plants), suggesting a lower basal rate of oxygen activation and H2O2 formation, leading to a relaxation of the antioxidant system. [ABSTRACT FROM AUTHOR]

Abstract: The rising atmospheric CO2 concentration resulting from industrial development may enhance photosynthesis and plant growth. However, there is a lack of research concerning the effect of combined factors such as CO2, temperature and water availability on plant regrowth following cutting or grazing, which represent the usual methods of managing forage legumes like alfalfa. Elevated CO2, temperature and drought can interact with cutting factors (e.g. cutting frequency or height), and source-sink balance differences before and after defoliation can modify photosynthetic behaviour and dry matter accumulation, as well as dry matter partitioning between above- and belowground organs. The aim of our study was to determine the interactive effect of CO2 (ambient, around 350μmolmol−1 versus 700μmolmol−1), temperature (ambient versus ambient+4°C) and water availability (well-irrigated versus partially irrigated) on dry matter partitioning and photosynthesis in nodulated alfalfa after vegetative normal growth and during regrowth. At the end of vegetative normal growth, CO2 enhanced dry matter accumulation despite photosynthesis being down-regulated at the end of this period. Photosynthesis was stimulated by elevated CO2 and resulted in greater dry matter accumulation during the regrowth period. Aboveground organs were affected more by drought than belowground organs during the entire experiment, particularly during vegetative normal growth. The higher drought tolerance (greater growth) observed during the regrowth period may be related to higher mass and greater reserves accumulated in the roots of plants. [Copyright &y& Elsevier]

Rising atmospheric CO2 may increase potential net leaf photosynthesis under short-term exposure, but this response decreases under long-term exposure because plants acclimate to elevated CO2 concentrations through a process known as downregulation. One of the main factors that may influence this phenomenon is the balance between sources and sinks in the plant. The usual method of managing a forage legume like alfalfa requires the cutting of shoots and subsequent regrowth, which alters the source/sink ratio and thus photosynthetic behaviour. The aim of this study was to determine the effect of CO2 (ambient, around 350 vs. 700 µmol mol−1), temperature (ambient vs. ambient + 4° C) and water availability (well-irrigated vs. partially irrigated) on photosynthetic behaviour in nodulated alfalfa before defoliation and after 1 month of regrowth. At the end of vegetative normal growth, plants grown under conditions of elevated CO2 showed photosynthetic acclimation with lower photosynthetic rates, Vcmax and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) activity. This decay was probably a consequence of a specific rubisco protein reduction and/or inactivation. In contrast, high CO2 during regrowth did not change net photosynthetic rates or yield differences in Vcmax or rubisco total activity. This absence of photosynthetic acclimation was directly associated with the new source-sink status of the plants during regrowth. After cutting, the higher root/shoot ratio in plants and remaining respiration can function as a strong sink for photosynthates, avoiding leaf sugar accumulation, the negative feed-back control of photosynthesis, and as a consequence, photosynthetic downregulation. [ABSTRACT FROM AUTHOR]

Abstract: 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 700μmolmol−1 CO2 maintained control nitrogen levels, discarding enhanced nitrogen availability as the main factor explaining enhanced dry matter. [Copyright &y& Elsevier]

We investigated the effectiveness of pre-drought treatment to acclimate a chilling-sensitive variety of maize (Errazu) against chilling injury. We tested two methods of applying drought: (a) withholding water during 17 d in perlite culture, and (b) suppressing water by keeping plants out of the nutrient solution at time intervals (2, 4. 6, 8 and 10 h) on five successive days in hydroponic culture. Drought treatments were applied to maize seedlings either in perlite or hydroponic culture before chilling (5 d at 5°C and 150 μmol m-2 s-1 photosynthetic photon fluence rate and then 5 d of recovery at 25 °C). Both experiments were carried out under low irradiance to avoid photo-oxidation damage during chilling. Plant growth (relative growth rate, RGR; net assimilation rate, NAR; leaf area ratio, LAR, specific leaf area, SLA; and leaf weight ratio, LWR), percentage of necrotic leaf area, leaf relative water content (RWC), leaf water (Ψleaf) and osmotic (Ψs) potentials, specific plant transpiration, total water absorption and CO2 exchange rate (CER) were examined in drought-treated and non-treated maize seedlings during chilling and after a 5 d recovery period. RGR and NAR of droughted maize seedlings were higher than those of non-droughted seedlings during recovery, irrespective of the growth medium (perlite or hydroponic). Chilling-induced leaf necrosis was significantly lower in droughted than in non-droughted seedlings. Droughted plants had higher water status (higher leaf RWC, Ψleaf and Ψs) after 5 d of chilling, mainly owing to stomatal closure induced by drought. The CER declined to a similar extent in droughted and non-droughted maize seedlings on chilling, but during recovery droughted seedlings showed significantly higher CO2 fixation rate than non-droughted seedlings. Leaf conductance of water vapour (g) and CO2 intercellular concentration (C1) analysis led to the conclusion that chilling-induced CER inhibition was not due to a stomatal limitation. Droughted seedlings of maize had a better water use efficiency of photosynthesis (WUEPh) than non-droughted plants. We conclude that pre-drought treatment hardened the chilling sensitive variety of maize Errazu against chilling injury. [ABSTRACT FROM AUTHOR]

Abstract: 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 700μmolmol−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. [Copyright &y& Elsevier]

The increase in the atmospheric CO 2 concentration is predicted to influence wheat production and grain quality and nutritional properties. In the present study, durum wheat ( Triticum durum Desf. cv. Sula) was grown under two different CO 2 (400 versus 700 μmol mol -1 ) concentrations to examine effects on the crop yield and grain quality at different phenological stages (from grain filling to maturity). Exposure to elevated CO 2 significantly increased aboveground biomass and grain yield components. Growth at elevated CO 2 diminished the elemental N content as well as protein and free amino acids, with a typical decrease in glutamine, which is the most represented amino acid in grain proteins. Such a general decrease in nitrogenous compounds was associated with altered kinetics of protein accumulation, N remobilization, and N partitioning. Our results highlight important modifications of grain metabolism that have implications for its nutritional quality.

C sink/source balance and N assimilation have been identified as target processes conditioning crop responsiveness to elevated CO2 . However, little is known about phenology-driven modifications of C and N primary metabolism at elevated CO2 in cereals such as wheat. Here, we examined the differential effect of elevated CO2 at two development stages (onset of flowering, onset of grain filling) in durum wheat (Triticum durum, var. Sula) using physiological measurements (photosynthesis, isotopes), metabolomics, proteomics and (15) N labelling. Our results show that growth at elevated CO2 was accompanied by photosynthetic acclimation through a lower internal (mesophyll) conductance but no significant effect on Rubisco content, maximal carboxylation or electron transfer. Growth at elevated CO2 altered photosynthate export and tended to accelerate leaf N remobilization, which was visible for several proteins and amino acids, as well as lysine degradation metabolism. However, grain biomass produced at elevated CO2 was larger and less N rich, suggesting that nitrogen use efficiency rather than photosynthesis is an important target for improvement, even in good CO2 -responsive cultivars., (© 2015 John Wiley & Sons Ltd.)

Many of the studies analysing the CO 2 effect on plant development have been conducted in optimal growth conditions. Furthermore, although some of those studies suggest that legumes might show a steady productivity increase with rising CO 2 , the role of nodule activity on the plant responsiveness to predicted atmospheric CO 2 enhancement is not well understood. In this study, C (metabolism and allocation) and N (nodule activity) interaction between the plant and the bacterial symbiont during the photosynthetic acclimation of N 2 -fixing alfalfa (Medicago sativa L. cv. Aragón) plants exposed to elevated CO 2 and temperature conditions was analysed. The plants were grown in temperature gradient greenhouses (TGG) where, in the case of elevated CO 2 treatments, the isotopic 13 C/ 12 C composition (δ 13 C) inside the TGG was modified. Compared with the corresponding temperature treatment, exposure to 700 μmol mol -1 CO 2 enhanced dry mass (DM) of plants in elevated temperature treatments (26%), whereas no significant effect was detected in ambient temperature treatments. The δ 13 C data revealed that although all the carbon corresponding to leaf total organic matter (TOM) came from newly assimilated C, plants exposed to elevated CO 2 did not develop strong sink activity (especially in ambient temperature conditions). Leaf carbohydrate build-up induced reduction in the Rubisco (E.C. 4.1.1.39) carboxylation capacity of plants. Despite this reduction in Rubisco content, plants exposed to elevated CO 2 conditions maintained (at ambient temperature) or increased (at elevated temperature) photosynthetic rates (measured at growth conditions) by increasing N use efficiency. The larger C sink strength of nodules in plants grown at elevated CO 2 and temperature conditions did not contribute towards overcoming photosynthetic acclimation. Further, the inhibitory effect of CO 2 on nodule total activity was caused by a large depletion in total soluble protein (TSP) of nodules. Depletion of leaf N demand, together with the reduction in nodule carbohydrate availability (as reflected by the nodule starch concentration), negatively affected the nodule TSP content and enzymatic activity.