Is vegetative area,photosynthesis, or grape C uploading involved in the climate change-related grape sugar/anthocyanin decoupling in Tempranillo?

Foreseen climate change is expected to impact on grape composition, both sugar and pigment content. We tested the hypothesis that interactions between main factors associated with climate change (elevated CO₂, elevated temperature, and water deficit) decouple sugars and anthocyanins, and explored the possible involvement of vegetative area, photosynthesis, and grape C uploading on the decoupling. Tempranillo grapevine fruit-bearing cuttings were exposed to CO₂ (700 vs. 400 ppm), temperature (ambient vs. +?4 °C), and irrigation levels (partial vs. full) in temperature-gradient greenhouses. In a search for mechanistic insights into the underlying processes, experiments 1 and 2 were designed to maximize photosynthesis and enlarge leaf area range among treatments, whereas plant growth was manipulated in order to deliberately down-regulate photosynthesis and control vegetative area in experiments 3 and 4. Towards this aim, treatments were applied either from fruit set to maturity with free vegetation and fully irrigated or at 5–8% of pot capacity (experiments 1 and 2), or from veraison to maturity with controlled vegetation and fully irrigated or at 40% of pot capacity (experiments 3 and 4). Modification of air ¹³C isotopic composition under elevated CO₂ enabled the further characterization of whole C fixation period and C partitioning to grapes. Increases of the grape sugars-to-anthocyanins ratio were highly and positively correlated with photosynthesis and grape ¹³C labeling, but not with vegetative area. Evidence is presented for photosynthesis, from fruit set to veraison, and grape C uploading, from veraison to maturity, as key processes involved in the establishment and development, respectively, of the grape sugars to anthocyanins decoupling.     

外源ALA对克瑞森无核葡萄叶片光合特性及果实品质的影响

以日光温室栽培的欧亚葡萄品种克瑞森无核为试验材料,在果实膨大期和始熟期采用不同浓度(50、100和150mg·L~(-1))5-氨基乙酰丙酸(ALA)喷施叶片和果穗,研究外源ALA处理对葡萄叶片光合特性、果实着色效果及果实品质的影响。结果表明:(1)各浓度ALA处理后葡萄叶片胞间CO_2浓度(Ci)、气孔导度(Gs)、蒸腾速率(Tr)、净光合速率(Pn)都有不同程度的增加,并以100mg·L~(-1) ALA处理效果最好。(2)50~150mg·L~(-1) ALA处理均能不同程度提高葡萄果皮花青素、叶绿素及类胡萝卜素含量,且各ALA处理的果实可溶性糖含量显著高于对照,但可滴定酸含量低于对照。(3)100和150mg·L~(-1) ALA处理能够显著改善果实成熟期的着色参数,且果实着色指数(CIRG)与花青素的积累呈现出良好的一致性。研究发现,在葡萄果实膨大期及始熟期喷施适宜浓度(100mg·L~(-1))ALA能够有效提高叶片光合性能,同时促进果实着色,显著改善果实外观色泽和果实品质。     

Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean

Effects of elevated atmospheric CO₂ (elevated CO₂ vs. ambient CO₂) and temperature (+0.67–0.79°C vs. ambient temperature) on the developmental life cycle of Spodoptera litura and the food utilization of the fourth‐instar larvae fed on soybean (resistant cultivar Lamar vs. susceptible landrace JLNMH) grown in open‐top chambers were studied from 2013 to 2015. The results indicated that: (i) compared with ambient CO₂, elevated CO₂ significantly prolonged the duration of larva and pupa, and adult longevity; significantly decreased the pupation rate, pupal weight, fecundity, the relative growth rate (RGR), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD); and increased the relative consumption rate (RCR) and approximate digestibility (AD). (ii) Compared with ambient temperature, elevated temperature significantly shortened the duration of larva and pupa; significantly decreased the pupal weight; and increased the RGR, RCR, ECD and ECI. (iii) Compared with the susceptible soybean accession JLNMH, the resistant soybean cultivar Lamar significantly prolonged the duration of larva and pupa; significantly decreased the pupation rate, pupal weight, adult longevity, fecundity and RGR, RCR and AD; and increased the indexes of ECD. (iv) At elevated temperature, S. litura fed on resistant vs. susceptible cultivars showed opposite trends in the RGR, RCR, AD, ECD and ECI. In addition, elevated temperature under elevated CO₂ significantly decreased the RGR (2014), ECD (2013 & 2014) and ECI (2013) and increased the AD (2013 & 2014) compared with other treatment combinations when S. litura fed on Lamar. Future climatic change of temperature and CO₂ concentration would likely affect growth and food utilization of S. litura, with increased food intake, but the reduced fecundity may compensate for the increased food consumption, resulting in no significant reduction in insect‐induced yield loss in soybean production. Nevertheless, use of insect resistant soybean cultivars will aid in ecological management of S. litura and reduce the insecticide load in soybean production.     

Temperature and enzymic control of malate metabolism in berries of Vitis vinifera

The specific activities of grape enzymes concerned with malic acid metabolism were determined at various stages of berry development under two temperature regimes. It was found that the lower acidity levels occurring in high temperature grapes at maturity are due to a changed pattern in acid breakdown rather than to reduced malic acid accumulation. The differences in acid disappearance cannot be explained by a shift in relative enzyme activities towards malate consumption with rising temperature.     

Berry composition and climate: responses and empirical models

Climate is a strong modulator of berry composition. Accordingly, the projected change in climate is expected to impact on the composition of berries and of the resultant wines. However, the direction and extent of climate change impact on fruit composition of winegrape cultivars are not fully known. This study utilised a climate gradient along a 700 km transect, covering all wine regions of Western Australia, to explore and empirically describe influences of climate on anthocyanins, pH and titratable acidity (TA) levels in two or three cultivars of Vitis vinifera (Cabernet Sauvignon, Chardonnay and Shiraz). The results showed that, at a common maturity of 22° Brix total soluble solids, berries from the warmer regions had low levels of anthocyanins and TA as well as high pH compared to berries from the cooler regions. Most of these regional variations in berry composition reflected the prevailing climatic conditions of the regions. Thus, depending on cultivar, 82–87 % of TA, 83 % of anthocyanins and about half of the pH variations across the gradient were explained by climate-variable-based empirical models. Some of the variables that were relevant in describing the variations in berry attributes included: diurnal ranges and ripening period temperature (TA), vapour pressure deficit in October and growing degree days (pH), and ripening period temperatures (anthocyanins). Further, the rates of change in these berry attributes in response to climate variables were cultivar dependent. Based on the observed patterns along the climate gradient, it is concluded that: (1) in a warming climate, all other things being equal, berry anthocyanins and TA levels will decline whereas pH levels will rise; and (2) despite variations in non-climatic factors (e.g. soil type and management) along the sampling transect, variations in TA and anthocyanins were satisfactorily described using climate-variable-based empirical models, indicating the overriding impact of climate on berry composition. The models presented here are useful tools for assessing likely changes in berry TA and anthocyanins in response to changing climate for the wine regions and cultivars covered in this study.     

Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modeling climate-induced geographic range shifts

Despite predictions that both atmospheric CO₂ concentrations and air temperature will rise together, very limited data are currently available to assess the possible interactive effects of these two global change factors on temperate forest tree species. Using yellow birch (Betula alleghaniensis) as a model species, we studied how elevated CO₂ (800 vs. 400 μl l⁻¹) influences seedling growth and physiological responses to a 5°C increase in summer air temperatures (31/26 vs. 26/21°C day/night), and how both elevated CO₂ and air temperature during the growing season influence seedling ability to survive freezing stress during the winter dormant season. Our results show that while increased temperature decreases seedling growth, temperature-induced growth reductions are significantly lower at elevated CO₂ concentrations (43% vs. 73%). The amelioration of high-temperature stress was related to CO₂-induced reductions in both whole-shoot dark respiration and transpiration. Our results also show that increased summer air temperature, and to a lesser degree CO₂ concentration, make dormant winter buds less susceptible to freezing stress. We show the relevance of these results to models used to predict how climate change will influence future forest species distribution and productivity, without considering the direct or interactive effects of CO_2. Received: 5 June 1997 / Accepted: 16 December 1997     

Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature

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.     

The physiological role of malic enzyme in grape ripening

The high specificity of malic enzyme (ME; EC 1.1.1.40) from grape berries (Vitis vinifera L.) for the naturally occurring l-enantiomer of malic acid, its very selective C₄-decarboxylation, and certain allosteric properties, reported previously, favour the conjecture of a regulatory function of ME in fruit malic acid degradation. On the other hand, high ME activity was detected even during the acid-accumulating phase of berry development. Also, the in vitro reversibility of the reaction supports the possibility of malate formation under conditions facilitating carboxylation of pyruvate, notably high CO₂/HCO ₃ ^- and NADPH/NADP ratios. However, a very limited incorporation of ¹⁴C into malate and the uniform labeling pattern of the dicarboxylic acid after administration of [U-¹⁴C] alanine to grape berries before and after the onset of ripening, indicate that the reverse reaction does not contribute essentially to grape malate synthesis. A regulatory mechanism mediating malic acid remetabolization on the basis of cosubstrate availability, comparable to the control of the hexose monophosphate shunt, is discussed.Abbreviation ME Malic enzyme (l-malate: NADP oxidoreductase)     

Responses of grape berry anthocyanin and titratable acidity to the projected climate change across the Western Australian wine regions

More than a century of observations has established that climate influences grape berry composition. Accordingly, the projected global climate change is expected to impact on grape berry composition although the magnitude and direction of impact at regional and subregional scales are not fully known. The aim of this study was to assess potential impacts of climate change on levels of berry anthocyanin and titratable acidity (TA) of the major grapevine varieties grown across all of the Western Australian (WA) wine regions. Grape berry anthocyanin and TA responses across all WA wine regions were projected for 2030, 2050 and 2070 by utilising empirical models that link these berry attributes and climate data downscaled (to ～5 km resolution) from the csiro_mk3_5 and miroc3_2_medres global climate model outputs under IPCC SRES A2 emissions scenario. Due to the dependence of berry composition on maturity, climate impacts on anthocyanin and TA levels were assessed at a common maturity of 22 °Brix total soluble solids (TSS), which necessitated the determination of when this maturity will be reached for each variety, region and warming scenario, and future period. The results indicate that both anthocyanin and TA levels will be affected negatively by a warming climate, but the magnitude of the impacts will differ between varieties and wine regions. Compared to 1990 levels, median anthocyanins concentrations are projected to decrease, depending on global climate model, by up to 3–12 % and 9–33 % for the northern wine regions by 2030 and 2070, respectively while 2–18 % reductions are projected in the southern wine regions for the same time periods. Patterns of reductions in the median Shiraz berry anthocyanin concentrations are similar to that of Cabernet Sauvignon; however, the magnitude is lower (up to 9–18 % in southern and northern wine regions respectively by 2070). Similarly, uneven declines in TA levels are projected across the study regions. The largest reductions in median TA are likely to occur in the present day warmer wine regions, up to 40 % for Chardonnay followed by 15 % and 12 % for Shiraz and Cabernet Sauvignon, respectively, by 2070 under the high warming projection (csiro_mk3_5). It is concluded that, under existing management practices, some of the key grape attributes that are integral to premium wine production will be affected negatively by a warming climate, but the magnitudes of the impacts vary across the established wine regions, varieties, the magnitude of warming and future periods considered.     

Interactive direct and plant‐mediated effects of elevated atmospheric [CO2] and temperature on a eucalypt‐feeding insect herbivore

Understanding the direct and indirect effects of elevated [CO₂] and temperature on insect herbivores and how these factors interact are essential to predict ecosystem‐level responses to climate change scenarios. In three concurrent glasshouse experiments, we measured both the individual and interactive effects of elevated [CO₂] and temperature on foliar quality. We also assessed the interactions between their direct and plant‐mediated effects on the development of an insect herbivore of eucalypts. Eucalyptus tereticornis saplings were grown at ambient or elevated [CO₂] (400 and 650 μmol mol^?1 respectively) and ambient or elevated ( + 4 °C) temperature for 10 months. Doratifera quadriguttata (Lepidoptera: Limacodidae) larvae were feeding directly on these trees, on their excised leaves in a separate glasshouse, or on excised field‐grown leaves within the temperature and [CO₂] controlled glasshouse. To allow insect gender to be determined and to ensure that any sex‐specific developmental differences could be distinguished from treatment effects, insect development time and consumption were measured from egg hatch to pupation. No direct [CO₂] effects on insects were observed. Elevated temperature accelerated larval development, but did not affect leaf consumption. Elevated [CO₂] and temperature independently reduced foliar quality, slowing larval development and increasing consumption. Simultaneously increasing both [CO₂] and temperature reduced these shifts in foliar quality, and negative effects on larval performance were subsequently ameliorated. Negative nutritional effects of elevated [CO₂] and temperature were also independently outweighed by the direct positive effect of elevated temperature on larvae. Rising [CO₂] and temperature are thus predicted to have interactive effects on foliar quality that affect eucalypt‐feeding insects. However, the ecological consequences of these interactions will depend on the magnitude of concurrent temperature rise and its direct effects on insect physiology and feeding behaviour.     

Growth dynamics and genotypic variation in tropical, field-grown paddy rice (Oryza sativa L.) in response to increasing carbon dioxide and temperature

While previous studies have examined the growth and yield response of rice to continued increases in CO₂ concentration and potential increases in air temperature, little work has focused on the long-term response of tropical paddy rice (i.e. the bulk of world rice production) in situ, or genotypic differences among cultivars in response to increasing CO₂ and/or temperature. At the International Rice Research Institute, rice (cv IR72) was grown from germination until maturity for 4 field seasons, the 1994 and 1995 wet and the 1995 and 1996 dry seasons at three different CO₂ concentrations (ambient, ambient + 200 and ambient + 300 μL L^–1 CO₂) and two air temperatures (ambient and ambient + 4 °C) using open-top field chambers placed within a paddy site. Overall, enhanced levels of CO₂ alone resulted in significant increases in total biomass at maturity and increased seed yield with the relative degree of enhancement consistent over growing seasons across both temperatures. Enhanced levels of temperature alone resulted in decreases or no change in total biomass and decreased seed yield at maturity across both CO₂ levels. In general, simultaneous increases in air temperature as well as CO₂ concentration offset the stimulation of biomass and grain yield compared to the effect of CO₂ concentration alone. For either the 1995 wet and 1996 dry seasons, additional cultivars (N-22, NPT1 and NPT2) were grown in conjunction with IR72 at the same CO₂ and temperature treatments. Among the cultivars tested, N-22 showed the greatest relative response of both yield and biomass to increasing CO₂, while NPT2 showed no response and IR72 was intermediate. For all cultivars, however, the combination of increasing CO₂ concentration and air temperature resulted in reduced grain yield and declining harvest index compared to increased CO₂ alone. Data from these experiments indicate that (a) rice growth and yield can respond positively under tropical paddy conditions to elevated CO₂, but that simultaneous exposure to elevated temperature may negate the CO₂ response to grain yield; and, (b) sufficient intraspecific variation exists among cultivars for future selection of rice cultivars which may, potentially, convert greater amounts of CO₂ into harvestable yield.     

Interactive effects of elevated CO2 and temperature on the leaf-miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson's Curse, Echium plantagineum (Boraginaceae)

Doubling of the current atmospheric CO₂ concentration, and an increase in global mean annual temperatures of 1.5–6 °C, have been predicted to occur by the end of this century. Whilst the separate effects of CO₂ and temperature on plant–insect interactions have been examined in a number of studies, few have investigated their combined impact. We carried out a factorial experiment to explore the effect of a doubling of CO₂ concentration and a 3 °C temperature increase on the development of a complete generation of the leaf‐miner, Dialectica scalariella, in the host plant Paterson's Curse, Echium plantagineum. Elevated CO₂ increased biomass, reduced leaf N and increased C:N ratios in the host plants. Leaf thickness also increased under elevated CO₂, but only in the high‐temperature treatment. Female D. scalariella did not discriminate between plants grown at the different CO₂ levels when ovipositing, despite the reduction in foliage quality under elevated CO₂. Overall, the negative response of D. scalariella to elevated CO₂ was greater than for many species of free‐living insects, presumably because of the limited mobility imposed by the leaf‐mining habit. Development was accelerated at the high temperature and slowed under elevated CO₂. The net result was a reduction in development time of ～14 days in the elevated CO₂/high temperature treatment, compared to the ambient CO₂/low temperature treatment. Larval survivorship and adult moth weight were both affected by a significant interaction between CO₂ and temperature. At the low temperature, CO₂ had little effect on survivorship, but at the high temperature, survivorship was significantly reduced under elevated CO₂. Similarly, elevated CO₂ had a stronger negative effect on adult moth weight when combined with the high‐temperature treatment. A possible explanation for these results is that the high temperature accelerated insect development to such an extent that the larvae did not have sufficient feeding time to compensate for the poorer quality of the foliage. The frequency with which interactions between CO₂ and temperature affected both plant and insect performance in this study highlights the need for caution when predicting the effects of future climate change on plant–insect interactions from single‐factor experiments.     

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.     

Interacting effects of CO2 partial pressure and temperature on photosynthesis and calcification in a scleractinian coral

We show here that CO₂ partial pressure (pCO₂) and temperature significantly interact on coral physiology. The effects of increased pCO₂ and temperature on photosynthesis, respiration and calcification rates were investigated in the scleractinian coral Stylophora pistillata. Cuttings were exposed to temperatures of 25°C or 28°C and to pCO₂ values of ca. 460 or 760 μatm for 5 weeks. The contents of chlorophyll c₂ and protein remained constant throughout the experiment, while the chlorophyll a content was significantly affected by temperature, and was higher under the ‘high‐temperature–high‐pCO₂’ condition. The cell‐specific density was higher at ‘high pCO₂’ than at ‘normal pCO₂’ (1.7 vs. 1.4). The net photosynthesis normalized per unit protein was affected by both temperature and pCO₂, whereas respiration was not affected by the treatments. Calcification decreased by 50% when temperature and pCO₂ were both elevated. Calcification under normal temperature did not change in response to an increased pCO₂. This is not in agreement with numerous published papers that describe a negative relationship between marine calcification and CO₂. The confounding effect of temperature has the potential to explain a large portion of the variability of the relationship between calcification and pCO₂ reported in the literature, and warrants a re‐evaluation of the projected decrease of marine calcification by the year 2100.     

Effects of elevated CO2 and O3 on the rate and duration of grain growth and harvest index in spring wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) cv. Minaret was grown in open-top chambers (OTCs) in 1995 and 1996 under three carbon dioxide (CO₂) and two ozone (O₃) levels. Plants were harvested regularly between anthesis and maturity to examine the rate of grain growth (dG/dt; mg d^–1) and the rate of increase in harvest index (dHI/dt;% d^–1). The duration of grain filling was not affected by elevated CO₂ or O₃, but was 12 days shorter in 1995, when the daily mean temperature was over 3 °C higher than in 1996. Season-long exposure to elevated CO₂ (680 μmol mol^–1) significantly increased the rate of grain growth in both years and mean grain weight at maturity (MGW) was up to 11% higher than in the chambered ambient air control (chAA; 383 μmol mol^–1). However, the increase in final yield obtained under elevated CO₂ relative to the chAA control in 1996 resulted primarily from a 27% increase in grain number per unit ground area. dG/dt was significantly reduced by elevated O₃ under ambient CO₂ conditions in 1995, but final grain yield was not affected because of a concurrent increase in grain number. Neither dG/dt nor dHI/dt were affected by the higher mean O₃ concentrations applied in 1996 (77 vs. 66 nmol mol^–1); the differing effects of O₃ on grain growth in 1995 and 1996 observed in both the ambient and elevated CO₂ treatments may reflect the contrasting temperature environments experienced. Grain yield was nevetheless reduced under elevated O₃ in 1996, primarily because of a substantial decrease in grain number. The data obtained show that, although exposure to elevated CO₂ and O₃ individually or in combination may affect both dG/dt and dHI/dt, the presence of elevated CO₂ does not protect against substantial O₃-induced yield losses resulting from its direct deleterious impact on reproductive processes. The implications of these results for food production under future climatic conditions are considered.     

Rising atmospheric CO2 may affect oil quality and seed yield of sunflower (Helianthus annus L.)

The impact of rising atmospheric CO₂ on crop productivity and quality is very important for global food and nutritional security under the changing climatic scenario. A study was conducted to investigate the effect of elevated CO₂ on seed oil quality and yield in a sunflower hybrid DRSH 1 and variety DRSF 113, raised inside open top chambers and exposed to elevated CO₂ (550 ± 50 µl l^?1). Elevated CO₂ exposure significantly influenced the rate of photosynthesis, seed yield and the quality traits in both hybrid and variety. Plants grown under elevated CO₂ concentration showed 61–68 % gain in biomass and 35–46 % increase in seed yield of both the genotypes, but mineral nutrient and protein concentration decreased in the seeds. The reduction in seed protein was up to 13 %, while macro and micronutrients decreased drastically (up to 43 % Na in hybrid seeds) under elevated CO₂ treatment. However, oil content increased significantly in DRSF 113 (15 %). Carbohydrate seed reserves increased with similar magnitudes in both the genotypes under elevated CO₂ treatment (13 %). Fatty acid composition in seed oil contained higher proportion of unsaturated fatty acids (oleic and linoleic acid) under elevated CO₂ treatment, which is a desirable change in oil quality for human consumption. These findings conclude that rising atmospheric CO₂ in changing future climate can enhance biomass production and seed yield in sunflower and alter their seed oil quality in terms of increased concentration of unsaturated fatty acids compared with saturated fatty acids and lower seed proteins and mineral nutrients.     

Elevated CO2 may impair the beneficial effect of arbuscular mycorrhizal fungi on the mineral and phytochemical quality of lettuce

Arbuscular mycorrhizal fungi (AMF) can improve growth and nutritional quality of greenhouse‐grown lettuces cultivated at ambient CO₂. Moreover, mycorrhizal symbiosis is predicted to be important in defining plant responses to elevated atmospheric CO₂ concentrations. Our main objective was to assess the effects of elevated CO₂ on growth and nutritional quality of greenhouse‐grown lettuces inoculated or not with AMF. Results showed that the accumulation of mineral nutrients (e.g. P, Cu, Fe) and antioxidant compounds (carotenoids, phenolics, anthocyanins, ascorbate) induced by AMF in leaves of lettuces cultivated at ambient CO₂ may diminish or disappear under elevated CO₂. It is hypothesized that a relevant quantity of photoassimilates could be used for improving shoot growth and spreading mycorrhizal colonization in detriment to the secondary metabolism. However, important differences can be found among different cultivars of lettuces.     

Increased temperatures may safeguard the nutritional quality of crops under future elevated CO2 concentrations

Iron (Fe) and zinc (Zn) deficiencies are a global human health problem that may worsen by the growth of crops at elevated atmospheric CO₂ concentration (eCO₂). However, climate change will also involve higher temperature, but it is unclear how the combined effect of eCO₂ and higher temperature will affect the nutritional quality of food crops. To begin to address this question, we grew soybean (Glycine max) in a Temperature by Free‐Air CO₂ Enrichment (T‐FACE) experiment in 2014 and 2015 under ambient (400 μmol mol^?1) and elevated (600 μmol mol^?1) CO₂ concentrations, and under ambient and elevated temperatures (+2.7°C day and +3.4°C at night). In our study, eCO₂ significantly decreased Fe concentration in soybean seeds in both seasons (?8.7 and ?7.7%) and Zn concentration in one season (?8.9%), while higher temperature (at ambient CO₂ concentration) had the opposite effect. The combination of eCO₂ with elevated temperature generally restored seed Fe and Zn concentrations to levels obtained under ambient CO₂ and temperature conditions, suggesting that the potential threat to human nutrition by increasing CO₂ concentration may not be realized. In general, seed Fe concentration was negatively correlated with yield, suggesting inherent limitations to increasing seed Fe. In addition, we confirm our previous report that the concentration of seed storage products and several minerals varies with node position at which the seeds developed. Overall, these results demonstrate the complexity of predicting climate change effects on food and nutritional security when various environmental parameters change in an interactive manner.     

Stomatal responses of Douglas-fir seedlings to elevated carbon dioxide and temperature during the third and fourth years of exposure

Two major components of climate change, increasing atmospheric [CO₂] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO₂] and temperature on seasonal patterns of stomatal conductance (g_s), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO₂ (AC) or ambient + 180 µmol mol^?1 CO₂ (EC), and at ambient temperature (AT) or ambient + 3·5 °C (ET) in a full‐factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO₂] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO₂] significantly increased with seasonal increases in the needle‐to‐air vapour pressure deficit (D). Across CO₂ treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO₂] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO₂ supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between g_s and net photosynthetic rates. This study suggests that elevated [CO₂] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle‐level water loss and water use efficiency of Douglas‐fir seedlings.     

Seed production and seed quality in a calcareous grassland in elevated CO2

In diverse plant communities the relative contribution of species to community biomass may change considerably in response to elevated CO₂. Along with species‐specific biomass responses, reproduction is likely to change as well with increasing CO₂ and might further accelerate shifts in species composition. Here, we ask if, after 5 years of CO₂ exposure, seed production and seed quality in natural nutrient‐poor calcareous grassland are affected by elevated CO₂ (650 μ L L^?1 vs 360 μ L L^?1) and how this might affect long‐term community dynamics. The effect of elevated CO₂ on the number of flowering shoots (+ 24%, P < 0.01) and seeds (+ 29%, P = 0.06) at the community level was similar to above ground biomass responses in this year, suggesting that the overall allocation to sexual reproduction remained unchanged. Compared among functional groups of species we found a 42% increase in seed number (P < 0.01) of graminoids, a 33% increase (P = 0.07) in forbs, and no significant change in legumes (? 38%, n.s.) under elevated CO₂. Large responses particularly of two graminoid species and smaller responses of many forb species summed up to the significant or marginally significant increase in seed number of graminoids and forbs, respectively. In several species the increase in seed number resulted both from an increase in flowering shoots and an increase in inflorescence size. In most species, seeds tended to be heavier (+ 12%, P < 0.01), and N‐concentration of seeds was significantly reduced in eight out of 13 species. The fraction of germinating seeds did not differ between seeds produced in ambient and elevated CO₂, but time to germination was significantly shortened in two species and prolonged in one species when seeds had been produced in elevated CO₂. Results suggest that species specific increases in seed number and changes in seed quality will exert substantial cumulative effects on community composition in the long run.