Effects of manganese-excess on CO<Subscript>2</Subscript> assimilation,ribulose-1,5-bisphosphate carboxylase/oxygenase,carbohydrates and photosynthetic electron transport of leaves,and antioxidant systems of leaves and roots in <Emphasis Type="Italic">Citrus grandis</Emphasis>seedlings

Background  

Very little is known about the effects of manganese (Mn)-excess on citrus photosynthesis and antioxidant systems. Seedlings of sour pummelo (Citrus grandis) were irrigated for 17 weeks with nutrient solution containing 2 μM (control) or 500 μM (excess) MnSO₄. The objective of this study were to understand the mechanisms by which Mn-excess leads to a decrease in CO₂ assimilation and to test the hypothesis that Mn-induced changes in antioxidant systems differ between roots and leaves.     

Growth and photosynthetic response of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings to ozone and/or elevated carbon dioxide

We investigated the effects of ozone (O₃) and/or elevated CO₂ concentration ([CO₂]) on growth and photosynthetic traits of Fagus crenata seedlings. Two-year-old seedlings were grown in four experimental treatments comprising two O₃ treatments (charcoal-filtered air and 100 nmol mol⁻¹ O₃; 6 h/day, 3 days/week) in combination with two CO₂ treatments (350 and 700 μmol mol⁻¹) for 18 weeks in environmental control growth chambers. The four treatments were designated as control, elevated O₃, elevated CO₂, and elevated CO₂ + O₃. Dry matter growth of the seedlings was greater in elevated CO₂ + O₃ than in elevated CO₂. In elevated CO₂ + O₃, a marked increase of second-flush leaves, considered a compensative response to O₃, was observed. The net photosynthetic rate of first-flush leaves in elevated CO₂ + O₃ increased earlier and was maintained for a longer period of time than that in elevated CO₂. Because emergence of second-flush leaves of F. crenata is greatly affected by the amount of assimilation products of first-flush leaves in current year, we consider that an early increase in the net photosynthetic rate of first-flush leaves contributed to the marked increase in second-flush leaf emergence under elevated CO₂ + O₃. These results imply that we must account for changes in compensative capacity with respect to not only morphological traits but also phenological traits and physiological functions such as photosynthesis when evaluating effects of O₃ on F. crenata under elevated [CO₂].     

Elevated CO<Subscript>2</Subscript> reduces stomatal and metabolic limitations on photosynthesis caused by salinity in <Emphasis Type="Italic">Hordeum vulgare</Emphasis>

The future environment may be altered by high concentrations of salt in the soil and elevated [CO₂] in the atmosphere. These have opposite effects on photosynthesis. Generally, salt stress inhibits photosynthesis by stomatal and non-stomatal mechanisms; in contrast, elevated [CO₂] stimulates photosynthesis by increasing CO₂ availability in the Rubisco carboxylating site and by reducing photorespiration. However, few studies have focused on the interactive effects of these factors on photosynthesis. To elucidate this knowledge gap, we grew the barley plant, Hordeum vulgare (cv. Iranis), with and without salt stress at either ambient or elevated atmospheric [CO₂] (350 or 700 μmol mol⁻¹ CO₂, respectively). We measured growth, several photosynthetic and fluorescence parameters, and carbohydrate content. Under saline conditions, the photosynthetic rate decreased, mostly because of stomatal limitations. Increasing salinity progressively increased metabolic (photochemical and biochemical) limitation; this included an increase in non-photochemical quenching and a reduction in the PSII quantum yield. When salinity was combined with elevated CO₂, the rate of CO₂ diffusion to the carboxylating site increased, despite lower stomatal and internal conductance. The greater CO₂ availability increased the electron sink capacity, which alleviated the salt-induced metabolic limitations on the photosynthetic rate. Consequently, elevated CO₂ partially mitigated the saline effects on photosynthesis by maintaining favorable biochemistry and photochemistry in barley leaves.     

Effects of elevated CO2 on growth,calcification, and spectral dependence of photoinhibition in the coccolithophore Emiliania huxleyi (Prymnesiophyceae)1

We studied the effects of elevated CO₂ concentrations on cell growth, calcification, and spectral variation in the sensitivity of photosynthesis to inhibition by solar radiation in the globally important coccolithophore Emiliania huxleyi. Growth rates and chlorophyll a content per cell showed no significant differences between elevated (800 ppmv) and ambient (400 ppmv) CO₂ conditions. However, the production of organic carbon and the cell quotas for both carbon and nitrogen, increased under elevated CO₂ conditions, whilst particulate inorganic carbon production rates decreased under the same conditions. Biometric analyses of cells showed that coccoliths only presented significant differences due to treatments in the central area width. Most importantly, the size of the coccosphere decreased under elevated CO₂ conditions. The susceptibility of photosynthesis to inhibition by ultraviolet radiation (UVR) was estimated using biological weighting functions (BWFs) and a model that predicts photosynthesis under photosynthetically active radiation and UVR exposures. BWF results demonstrated that the sensitivity of photosynthesis to UVR was not significantly different between E. huxleyi cells grown under elevated and present CO₂ concentrations. We propose that the acclimation to elevated CO₂ conditions involves a physiological mechanism of regulation and allocation of energy and metabolites in the cell, which is also responsible for altering the sensitivity to UVR. In coccolithophores, this mechanism might be affected by the decrease in the calcification rates.     

A meta-analysis of plant physiological and growth responses to temperature and elevated CO<Subscript>2</Subscript>

Atmospheric carbon dioxide (CO₂) and global mean temperature are expected to be significantly higher by the end of the 21st century. Elevated CO₂ (eCO₂) and higher temperature each affect plant physiology and growth, but their interactive effects have not been reviewed statistically with respect to higher chronic mean temperatures and abrupt heat stress. In this meta-analysis, we examined the effect of CO₂ on the physiology and growth of plants subjected to different temperature treatments. The CO₂ treatments were categorized into ambient (<400 ppm) or elevated (>560 ppm) levels, while temperature treatments were categorized into ambient temperature (AT), elevated temperature (ET; AT + 1.4–6°C), or heat stress (HS; AT + >8°C). Plant species were grouped according to photosynthetic pathways (C₃, C₄), functional types (legumes, non-legumes), growth forms (herbaceous, woody), and economic purposes (crop, non-crop). eCO₂ enhanced net photosynthesis at AT, ET, and HS in C₃ species (especially at the HS level), but in C₄ species, it had no effect at AT, a positive effect at ET, and a negative effect at HS. The positive effect of eCO₂ on net photosynthesis was greater for legumes than for non-legumes at HS, for non-crops than crops at ET, and for woody than herbaceous species at ET and HS. Total (W _T) and above- (W _AG) and below-ground (W _BG) biomass were increased by eCO₂ for most species groups at all temperatures, except for C₄ species and W _BG of legumes at HS. Hence, eCO₂ × heat effects on growth were often not explained by effects on net photosynthesis. Overall, the results show that eCO₂ effects on plant physiology and growth vary under different temperature regimes, among functional groups and photosynthetic pathways, and among response variables. These findings have important implications for biomass accumulation and ecosystem functioning in the future when the CO₂ level is higher and climate extremes, such as heat waves, become more frequent.     

Changes in photosynthetic capacity,carboxylation efficiency,and CO2 compensation point associated with midday stomatal closure and midday depression of net CO2 exchange of leaves of Quercus suber

The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a standard time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO₂ pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO₂ uptake. Midday depression of CO₂ uptake is the result of i) a decrease in CO₂-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO₂ response curve (carboxylation efficiency), and iii) a substantial increase in the CO₂ compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO₂ pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO₂ may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.Abbreviations and symbols CE carboxylation efficiency - NP net photosynthesis rate - PAR photosynthetically active radiation - P_i leaf internal CO₂ partial pressure - W water vapor mole fraction difference between leaf and air - T CO₂ compensation pressure Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

Carbon balance in a monospecific stand of an annual herb <Emphasis Type="Italic">Chenopodium album</Emphasis> at an elevated CO<Subscript>2</Subscript> concentration

Elevated CO₂ enhances carbon uptake of a plant stand, but the magnitude of the increase varies among growth stages. We studied the relative contribution of structural and physiological factors to the CO₂ effect on the carbon balance during stand development. Stands of an annual herb Chenopodium album were established in open-top chambers at ambient and elevated CO₂ concentrations (370 and 700 μmol mol⁻¹). Plant biomass growth, canopy structural traits (leaf area, leaf nitrogen distribution, and light gradient in the canopy), and physiological characteristics (leaf photosynthesis and respiration of organs) were studied through the growing season. CO₂ exchange of the stand was estimated with a canopy photosynthesis model. Rates of light-saturated photosynthesis and dark respiration of leaves as related with nitrogen content per unit leaf area and time-dependent reduction in specific respiration rates of stems and roots were incorporated into the model. Daily canopy carbon balance, calculated as an integration of leaf photosynthesis minus stem and root respiration, well explained biomass growth determined by harvests (r ² = 0.98). The increase of canopy photosynthesis with elevated CO₂ was 80% at an early stage and decreased to 55% at flowering. Sensitivity analyses suggested that an alteration in leaf photosynthetic traits enhanced canopy photosynthesis by 40–60% throughout the experiment period, whereas altered canopy structure contributed to the increase at the early stage only. Thus, both physiological and structural factors are involved in the increase of carbon balance and growth rate of C. album stands at elevated CO₂. However, their contributions were not constant, but changed with stand development.     

Sensitivity of chickpea and faba bean to root‐zone hypoxia,elevated ethylene,and carbon dioxide

During soil waterlogging, plants experience O₂ deficits, elevated ethylene, and high CO₂ in the root‐zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L^?1), CO₂ (2–20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO₂ reduced root growth of both species, but O₂ deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO₂ inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas‐filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O₂ movement was more prominent in faba bean when in an O₂‐free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O₂, such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO₂ partially inhibited root extension in both species, but low O₂ in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O₂ condition than faba bean.     

Effects of desiccation and CO2 concentrations on emersed photosynthesis in Porphyra haitanensis (Bangiales,Rhodophyta), a species farmed in China

The effects on photosynthesis of CO₂ and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO₂ on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO₂ compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO₂ level (about 350?ml?m^?3), and doubling the CO₂ concentration (700?ml?m^?3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700?ml?m^?3 CO₂ was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO₂ concentration during emersion.     

Antagonistic actions of boron against inhibitory effects of aluminum toxicity on growth, CO2 assimilation, ribulose-1,5-bisphosphate carboxylase/oxygenase, and photosynthetic electron transport probed by the JIP-test, of Citrus grandis seedlings

Background  

Little information is available on the amelioration of boron (B) on aluminum (Al)-induced photosynthesis inhibition. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 4 B levels (2.5, 10, 25 and 50 μM H₃BO₃) × 2 Al levels (0 and 1.2 mM AlCl₃·6H₂O). The objectives of this study were to determine how B alleviates Al-induced growth inhibition and to test the hypothesis that Al-induced photosynthesis inhibition can be alleviated by B via preventing Al from getting into shoots.     

Genes and pathways for CO<Subscript>2</Subscript> fixation in the obligate,chemolithoautotrophic acidophile, <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis>, Carbon fixation in <Emphasis Type="Italic">A. ferrooxidans</Emphasis>

Background  

Acidithiobacillus ferrooxidans is chemolithoautotrophic γ-proteobacterium that thrives at extremely low pH (pH 1-2). Although a substantial amount of information is available regarding CO₂ uptake and fixation in a variety of facultative autotrophs, less is known about the processes in obligate autotrophs, especially those living in extremely acidic conditions, prompting the present study.     

Ozone effects on wheat in relation to CO2: modelling short‐term and long‐term responses of leaf photosynthesis and leaf duration

A combined stomatal–photosynthesis model was extended to simulate the effects of ozone exposure on leaf photosynthesis and leaf duration in relation to CO₂. We assume that ozone has a short‐term and a long‐term effect on the Rubisco‐limited rate of photosynthesis, A_c. Elevated CO₂ counteracts ozone damage via stomatal closure. Ozone is detoxified at uptake rates below a threshold value above which A_c decreases linearly with the rate of ozone uptake. Reduction in A_c is transient and depends on leaf age. Leaf duration decreases depending on accumulated ozone uptake. This approach is introduced into the mechanistic crop simulation model AFRCWHEAT2. The derived model, AFRCWHEAT2‐O3, is used to test the capability of these assumptions to explain responses at the plant and crop level. Simulations of short‐term and long‐term responses of leaf photosynthesis, leaf duration and plant and crop growth to ozone exposure in response to CO₂ are analysed and compared with experimental data derived from the literature. The model successfully reproduced published responses of leaf photosynthesis, leaf duration, radiation use efficiency and final biomass of wheat to elevated ozone and CO₂. However, simulations were unsatisfactory for cumulative radiation interception which had some impact on the accuracy of predictions of final biomass. There were responses of leaf‐area index to CO₂ and ozone as a result of effects on tillering which were not accounted for in the present model. We suggest that some model assumptions need to be tested, or analysed further to improve the mechanistic understanding of the combined effects of changes in ozone and CO₂ concentrations on leaf photosynthesis and senescence. We conclude that research is particularly needed to improve the understanding of leaf‐area dynamics in response to ozone exposure and elevated CO₂.     

Gas exchange and photosynthetic performance of the tropical tree <Emphasis Type="Italic">Acacia nigrescens</Emphasis> when grown in different CO<Subscript>2</Subscript> concentrations

The photosynthetic responses of the tropical tree species Acacia nigrescens Oliv. grown at different atmospheric CO₂ concentrations—from sub-ambient to super-ambient—have been studied. Light-saturated rates of net photosynthesis (A _sat) in A. nigrescens, measured after 120 days exposure, increased significantly from sub-ambient (196 μL L⁻¹) to current ambient (386 μL L⁻¹) CO₂ growth conditions but did not increase any further as [CO₂] became super-ambient (597 μL L⁻¹). Examination of photosynthetic CO₂ response curves, leaf nitrogen content, and leaf thickness showed that this acclimation was most likely caused by reduction in Rubisco activity and a shift towards ribulose-1,5-bisphosphate regeneration-limited photosynthesis, but not a consequence of changes in mesophyll conductance. Also, measurements of the maximum efficiency of PSII and the carotenoid to chlorophyll ratio of leaves indicated that it was unlikely that the pattern of A _sat seen was a consequence of growth [CO₂] induced stress. Many of the photosynthetic responses examined were not linear with respect to the concentration of CO₂ but could be explained by current models of photosynthesis.     

Seasonal physiological responses and biomass growth in a bioenergy crop (<Emphasis Type="Italic">Phalaris arundinacea</Emphasis> L.) under elevated temperature and CO<Subscript>2</Subscript>, subjected to different water regimes in boreal conditions

We investigated the seasonal variability of effects of elevated temperature (+3.5°C), CO₂ elevation (700 μmol mol⁻¹) and varying water regimes (high to low water content) on physiological responses and biomass growth of reed canary grass (Phalaris arundinacea L., local field-grown cultivar) grown in a boreal environment. In controlled environment greenhouses, various physiological and growth parameters of grass, i.e., light-saturated net photosynthetic rates (P _nmax), water use efficiency (WUE) and optimal photochemical efficiency of photosystem II (F _v/F _m), and leaf area development and biomass of plant organs (leaf, stem, coarse, and fine root) were measured. During the early measurement periods, elevated temperature enhanced leaf photosynthesis and above-ground biomass of reed canary grass; however, this resulted in earlier senescence and lower biomass at the end of measurement period, compared to ambient temperature. This effect was more pronounced under water limitation. Elevated CO₂ enhanced P _nmax, WUE, and leaf area and total plant biomass (above- and below-ground) over growing season. The explanation for imbalance between stimulated photosynthesis and increase in above-ground biomass was that CO₂ enrichment causes a greater increase in the plant’s root system. The combination of elevated temperature and CO₂ slightly increases the growth of plant. Adequate water availability favored photosynthesis and biomass growth of reed canary grass. The temperature- and drought-induced stresses were partially mitigated by elevated CO₂. Other cultivars should be tested in order to identify those that are better adapted to elevated temperatures and CO₂ and variable water levels.     

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.     

Combined effects of warming and elevated CO2 on the impact of drought in grassland species

Aims

Drought is a major growth limiting factor in the majority of terrestrial ecosystems and is expected to become more frequent in the future. Therefore, resolving the drought response of plants under changing climate conditions is crucial to our understanding of future ecosystem functioning. This study responds to the need for experimental research on the combined effects of warming, elevated CO₂ and drought, and aims to determine whether the response to drought is altered under future climate conditions.

Methods

Two grassland species, Lolium perenne L. and Plantago lanceolata L., were grown in sunlit climate-controlled chambers. Four climates were simulated: (1) current climate, (2) current climate with drought, (3) a warmer climate with drought, and (4) a climate with combined warming, elevated CO₂ and drought.

Results

Warming did not alter the drought response, neither directly through photosynthesis nor indirectly through changes in water consumption. Also for combined warming and elevated CO₂ there were no effects on the plant response to drought for any of the measured parameters. However, simultaneous warming and elevated CO₂ mitigated the biomass response to drought through a positive pre-drought effect on photosynthesis and biomass response.

Conclusions

Our results indicate that a positive pre-drought effect of combined warming and elevated CO₂ has the potential to compensate for drought-induced biomass losses under future climate conditions.     

C4 photosynthesis and water stress

Background

In contrast to C₃ photosynthesis, the response of C₄ photosynthesis to water stress has been less-well studied in spite of the significant contribution of C₄ plants to the global carbon budget and food security. The key feature of C₄ photosynthesis is the operation of a CO₂-concentrating mechanism in the leaves, which serves to saturate photosynthesis and suppress photorespiration in normal air. This article reviews the current state of understanding about the response of C₄ photosynthesis to water stress, including the interaction with elevated CO₂ concentration. Major gaps in our knowledge in this area are identified and further required research is suggested.

Scope

Evidence indicates that C₄ photosynthesis is highly sensitive to water stress. With declining leaf water status, CO₂ assimilation rate and stomatal conductance decrease rapidly and photosynthesis goes through three successive phases. The initial, mainly stomatal phase, may or may not be detected as a decline in assimilation rates depending on environmental conditions. This is because the CO₂-concentrating mechanism is capable of saturating C₄ photosynthesis under relatively low intercellular CO₂ concentrations. In addition, photorespired CO₂ is likely to be refixed before escaping the bundle sheath. This is followed by a mixed stomatal and non-stomatal phase and, finally, a mainly non-stomatal phase. The main non-stomatal factors include reduced activity of photosynthetic enzymes; inhibition of nitrate assimilation, induction of early senescence, and changes to the leaf anatomy and ultrastructure. Results from the literature about CO₂ enrichment indicate that when C₄ plants experience drought in their natural environment, elevated CO₂ concentration alleviates the effect of water stress on plant productivity indirectly via improved soil moisture and plant water status as a result of decreased stomatal conductance and reduced leaf transpiration.

Conclusions

It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C₄ photosynthesis. This may explain why C₄ photosynthesis is equally or even more sensitive to water stress than its C₃ counterpart in spite of the greater capacity and water use efficiency of the C₄ photosynthetic pathway.Key words: C₃ and C₄ photosynthesis, stomatal and non-stomatal limitation, high CO₂, water stress     

Physiological and biochemical aspects and molecular mechanisms of plant adaptation to the elevated concentration of atmospheric CO<Subscript>2</Subscript>

The review of publications concerning the impact of increasing CO₂ concentration in the Earths atmosphere (C_a) on higher terrestrial plants. The physiological changes in plants induced by increasing C_a, including growth and biochemical composition, the characteristics of photosynthesis and respiration, as well as the molecular mechanisms of the regulation of the activity of most important biosynthetic enzymes at early and late stages of the exposure to elevated C_a are under consideration. Various concepts of metabolic regulation during acclimation to increasing CO₂ concentration are critically reviewed. The pathways of possible involvement of carbonic anhydrase-mediated systems of CO₂ transport and concentration during C₃ photosynthesis of higher plants, the metabolic and signal mechanisms of photosynthesis inhibition by carbohydrates and the role of ethylene at elevated C_a are presented. The effect of elevated C_a on plant development and source-sink relations, as well as its interaction with other environmental factors, such as mineral, primarily nitrogen nutrition, light, temperature, and water regime, are discussed in with the context of potential forecasting of the consequences of increase in C_a and temperature for the activities of various higher plant forms in the rapidly changing climate.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 129–145.Original Russian Text Copyright © 2005 by Romanova.     

The influence of increased temperature and carbon dioxide levels on the benthic/sea ice diatom <Emphasis Type="Italic">Navicula</Emphasis><Emphasis Type="Italic">directa</Emphasis>

Polar oceans are very susceptible to increased levels of atmospheric CO₂ and may act as the world’s largest sink for anthropogenic CO₂. Simultaneously, as atmospheric CO₂ increases, sea surface temperature rises due to global warming. These two factors are important in regulating microalgal ecophysiology, and it has been suggested that future global changes may significantly alter phytoplankton species composition. This study aims to investigate potential consequences of global change in terms of increased temperature and CO₂ enrichment on the benthic/sea ice diatom Navicula directa. In a laboratory experiment, the physiological response to elevated temperature and partial pressure of CO₂ (pCO₂) was investigated in terms of growth, photosynthetic activity and photosynthetic pigment composition. The experiment was performed under manipulated levels of pCO₂ (380 and 960 ppm) and temperature (0.5 and 4.5°C) to simulate a change from present levels to predicted levels during a worst-case scenario by the year 2100. After 7 days of treatment, no synergetic effects between temperature and pCO₂ were detected. However, elevated temperature promoted effective quantum yield of photosynthesis (∆F/F￠_m F^\prime_{\rm m} ) and increased growth rates by approximately 43%. Increased temperature also resulted in an altered pigment composition. In addition, enrichment of CO₂ appeared to reduce specific growth rates of N. directa. Even though growth rates were only reduced by approximately 5%, we hereby report that increased pCO₂ levels might also have potential negative effects on certain diatom strains.     

An automated growth enclosure for metabolic labeling of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> with <Superscript>13</Superscript>C-carbon dioxide - an <Emphasis Type="Italic">in vivo</Emphasis> labeling system for proteomics and metabolomics research

Background  

Labeling whole Arabidopsis (Arabidopsis thaliana) plants to high enrichment with ¹³C for proteomics and metabolomics applications would facilitate experimental approaches not possible by conventional methods. Such a system would use the plant's native capacity for carbon fixation to ubiquitously incorporate ¹³C from ¹³CO₂ gas. Because of the high cost of ¹³CO₂ it is critical that the design conserve the labeled gas.