Elevated CO<Subscript>2</Subscript> influences herbivory-induced defense responses of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

We experimentally demonstrate that elevated CO₂ can modify herbivory-induced plant chemical responses in terms of both total and individual glucosinolate concentrations. Overall, herbivory by larvae of diamondback moths (Plutella xylostella) resulted in no change in glucosinolate levels of the annual plant Arabidopsis thaliana under ambient CO₂ conditions. However, herbivory induced a significant 28–62% increase in glucosinolate contents at elevated CO₂. These inducible chemical responses were both genotype-specific and dependent on the individual glucosinolate considered. Elevated CO₂ can also affect structural defenses such as trichomes and insect-glucosinolate interactions. Insect performance was significantly influenced by specific glucosinolates, although only under CO₂ enrichment. This study can have implications for the evolution of inducible defenses and coevolutionary adaptations between plants and their associated herbivores in future changing environments.     

Innate and evolutionarily increased advantages of invasive <Emphasis Type="Italic">Eupatorium adenophorum</Emphasis> over native <Emphasis Type="Italic">E. japonicum</Emphasis> under ambient and doubled atmospheric CO<Subscript>2</Subscript> concentrations

Both innate and evolutionarily increased ecophysiological advantages can contribute to vigorous growth, and eventually to invasiveness of alien plants. Little effort has been made to explore the roles of innate factors of alien plants in invasiveness and the effects of CO₂ enrichment on alien plant invasions. To address these problems, we compared invasive Eupatorium adenophorum, its native conspecific, and a native congener (E. japonicum) under ambient and doubled atmospheric CO₂ concentrations. Native E. adenophorum from Mexico grew slower than invasive E. adenophorum but faster than native E. japonicum under both CO₂ concentrations. The faster growth rate of invasive E. adenophorum was associated with higher photosynthetic capacity and leaf area ratio. For invasive E. adenophorum, the higher photosynthetic capacity was associated with higher nitrogen (N) allocation to photosynthesis, which was related to lower leaf mass per area; the higher leaf area ratio was due to lower leaf mass per area and higher leaf mass fraction. Tradeoff between N allocations to photosynthesis versus defenses was found. CO₂ enrichment significantly increased relative growth rate and biomass accumulation by increasing actual photosynthetic rate for all studied materials. However, the relative increase in growth was not significantly different among them. CO₂ enrichment did not influence N allocation to photosynthesis, but increased N allocation to cell walls. The reduced leaf N content decreased N content in photosynthesis, explaining the down-regulation of photosynthetic capacity under prolonged elevated CO₂ concentration. Our results indicate that both innate and evolutionary advantages in growth and related ecophysiological traits contribute to invasiveness of invasive E. adenophorum, and CO₂ enrichment may not aggravate E. adenophroum’s invasion in the future.     

Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) growth and nitrogen distribution under elevated CO<Subscript>2</Subscript> concentration and air temperature

A field experiment was conducted to investigate the effects of elevated atmospheric CO₂ concentration and temperature, singly and in combination, on grain yield and the distribution of nitrogen (N) in different rice organs. The rice ‘Wuyunjing 23’ was planted under four treatments: ambient CO₂ and temperature (ACT), elevated CO₂ (200 μmol mol^?1 higher than ambient CO₂) (EC), elevated temperature (1 °C above the ambient temperature) (ET), and the combination of elevated CO₂ and temperature (ECT) under T-FACE (temperature and CO₂ free air controlled enrichment) system. CO₂-induced increment and temperature-induced reduction in grain yield was 6.0 and 25.2% in 2013, and that was 9.8 and 10.8% in 2014, respectively. Dry matter (DM) production in different organs increased under EC at vegetative stage but decreased under ET at reproductive stage. The negative effects of temperature on grain yield and DM was weakened when combined with CO₂ enrichment. And the trends of decrease for yield and DM under ET and ECT in 2013 were more obvious than those in 2014 due to the annual temperature differences. Furthermore, ET led to greater distribution of N in root and stem but not for panicle than that under ACT. These mainly demonstrated that the rice production would be suffered varying degree of loss under global warming in future although the CO₂ enrichment could alleviate the effects of high temperature on rice growth.     

Strong effects of hydrologic environment and weak effects of elevated CO<Subscript>2</Subscript> on the invasive weed <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and the biocontrol beetle <Emphasis Type="Italic">Agasicles hygrophila</Emphasis>

Global change, such as elevated CO₂, may alter interactions between invasive plants and biocontrol agents, impacting biocontrol efficacy. Here, we conducted four experiments in Texas, USA to test how elevated CO₂ influences an invasive plant (Alternanthera philoxeroides) and its interactions with an introduced biocontrol beetle (Agasicles hygrophila) in terrestrial (well-watered) and flooded environments. We grew plants for 9 months in ambient or elevated CO₂ (800 ppm) chambers in continuously flooded or well-watered conditions. In no-choice trials, flooding increased leaf toughness and decreased beetle consumption but beetles only oviposited on ambient CO₂ leaves. In choice trials, beetles preferred to feed and oviposit on terrestrial plants but were also less likely to damage elevated CO₂ leaves. Caged beetle populations were larger in terrestrial conditions than aquatic conditions for a second set of plants grown in the chambers. With a third set of plants grown in the ambient or elevated CO₂ chambers, damage for plants placed in the field (aquatic setting) was higher for plants grown in terrestrial conditions vs. flooded conditions at ambient CO₂. Our results suggest that elevated CO₂ will have minor effects on the efficacy of this biocontrol agent by decreasing oviposition and number of leaves damaged, and hydrologic environment may affect invasive plant performance by altering herbivore oviposition and feeding preferences. A broader understanding of the effects of global change on biocontrol will help prevent and manage future spread of invasive plants.     

Different CO<Subscript>2</Subscript> acclimation strategies in juvenile and mature leaves of <Emphasis Type="Italic">Ottelia alismoides</Emphasis>

The freshwater macrophyte, Ottelia alismoides, is a bicarbonate user performing C4 photosynthesis in the light, and crassulacean acid metabolism (CAM) when acclimated to low CO₂. The regulation of the three mechanisms by CO₂ concentration was studied in juvenile and mature leaves. For mature leaves, the ratios of phosphoenolpyruvate carboxylase (PEPC) to ribulose-bisphosphate carboxylase/oxygenase (Rubisco) are in the range of that of C4 plants regardless of CO₂ concentration (1.5–2.5 at low CO₂, 1.8–3.4 at high CO₂). In contrast, results for juvenile leaves suggest that C4 is facultative and only present under low CO₂. pH-drift experiments showed that both juvenile and mature leaves can use bicarbonate irrespective of CO₂ concentration, but mature leaves have a significantly greater carbon-extracting ability than juvenile leaves at low CO₂. At high CO₂, neither juvenile nor mature leaves perform CAM as indicated by lack of diurnal acid fluctuation. However, CAM was present at low CO₂, though the fluctuation of titratable acidity in juvenile leaves (15–17 µequiv g^?1 FW) was slightly but significantly lower than in mature leaves (19–25 µequiv g^?1 FW), implying that the capacity to perform CAM increases as leaves mature. The increased CAM activity is associated with elevated PEPC activity and large diel changes in starch content. These results show that in O. alismoides, carbon-dioxide concentrating mechanisms are more effective in mature compared to juvenile leaves, and C4 is facultative in juvenile leaves but constitutive in mature leaves.     

Fine root turnover of Japanese white birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> var. <Emphasis Type="Italic">japonica</Emphasis>) grown under elevated CO<Subscript>2</Subscript> in northern Japan

Key message

Elevated CO ₂ reduced fine root dynamics (production and turnover) of white birch seedlings, especially grown in volcanic ash soil compared with brown forest soil.

Abstract

Increased atmospheric CO₂ usually enhances photosynthetic ability and growth of trees. To understand how increased CO₂ affects below-ground part of trees under varied soil condition, we investigated the responses of the fine root (diameter <2 mm) dynamics of Japanese white birch (Betula platyphylla var. japonica) which was planted in 2010. The three-year-old birch seedlings were grown in four experimental treatments comprising two levels of CO₂, i.e., ambient: 380–390 and elevated: 500 μmol mol^?1, in combination with two kinds of soil: brown forest (BF) soil and volcanic ash (VA) soil which has few nutrients. The growth and turnover of fine roots were measured for 3 years (2011–2013) using the Mini-rhizotron. In the first observation year, live fine root length (standing crop) in BF soil was not affected by CO₂ treatment, but it was reduced by the elevated CO₂ from the second observation year. In VA soil, live fine root length was reduced by elevated CO₂ for all 3 years. Fine root turnover tended to decrease under elevated CO₂ compared with ambient in both soil types during the first and second observation years. Turnover of fine root production and mortality was also affected by the two factors, elevated CO₂ and different soil types. Median longevity of fine root increased under elevated CO₂, especially in VA soil at the beginning, and a shorter fine root lifespan appeared after 2 years of observation (2011–2012). These results suggest that elevated CO₂ does not consistently stimulate fine root turnover, particularly during the plant seedlings stage, as it may depend on the costs and benefits of constructing and retaining roots. Therefore, despite the other uncontrollable environment factors, carbon sequestration to the root system may be varied by CO₂ treatment period, soil type and plant age.

     

Growth and reproduction of the alpine grasshopper <Emphasis Type="Italic">Miramella alpina</Emphasis> feeding on CO<Subscript>2</Subscript>-enriched dwarf shrubs at treeline

The consequences for plant-insect interactions of atmospheric changes in alpine ecosystems are not well understood. Here, we tested the effects of elevated CO₂ on leaf quality in two dwarf shrub species (Vaccinium myrtillus and V. uliginosum) and the response of the alpine grasshopper (Miramella alpina) feeding on these plants in a field experiment at the alpine treeline (2,180 m a.s.l.) in Davos, Switzerland. Relative growth rates (RGR) of M. alpina nymphs were lower when they were feeding on V. myrtillus compared to V. uliginosum, and were affected by elevated CO₂ depending on plant species and nymph developmental stage. Changes in RGR correlated with CO₂-induced changes in leaf water, nitrogen, and starch concentrations. Elevated CO₂ resulted in reduced female adult weight irrespective of plant species, and prolonged development time on V. uliginosum only, but there were no significant differences in nymphal mortality. Newly molted adults of M. alpina produced lighter eggs and less secretion (serving as egg protection) under elevated CO₂. When grasshoppers had a choice among four different plant species grown either under ambient or elevated CO₂, V. myrtillus and V. uliginosum consumption increased under elevated CO₂ in females while it decreased in males compared to ambient CO₂-grown leaves. Our findings suggest that rising atmospheric CO₂ distinctly affects leaf chemistry in two important dwarf shrub species at the alpine treeline, leading to changes in feeding behavior, growth, and reproduction of the most important insect herbivore in this system. Changes in plant-grasshopper interactions might have significant long-term impacts on herbivore pressure, community dynamics and ecosystem stability in the alpine treeline ecotone.     

Elevated CO<Subscript>2</Subscript> increases energy-use efficiency of invasive <Emphasis Type="Italic">Wedelia trilobata</Emphasis> over its indigenous congener

Increasing atmospheric CO₂ concentration is regarded as an important factor facilitating plants invasions by stimulating invasive species growth. However, the physiological mechanisms by which invasive plants increase at the expense of existing native plants are poorly understood. Plant growth is always related to energy-use process including energy assimilation and expenditure, and thus examination of energetic properties could provide mechanistic insight into growth responses to increased CO₂. The aims of this study were to examine the effect of rising CO₂ on the growth and energetic properties of alien invasive species (Wedelia trilobata (L.) Hitchc.) and its native congener (Wedelia chinensis (Osbeck.) Merr.) in South China, and to determine if the specific energetic properties of invasive species at elevated CO₂ favoring its growth. Elevated CO₂ stimulated a greater increase in biomass production for invasive W. trilobata (58.9%) than for its indigenous congener (48.1%). Meanwhile, elevated CO₂ altered the energetic properties differently upon species. For invasive W. trilobata, elevated CO₂ significantly increased total energetic gain via photosynthetic activity (A _total), but decreased energetic cost of biomass construction (CC), and thus enhanced photosynthetic energy-use efficiency (PEUE) by 85.3%. In contrast, the indigenous W. chinensis showed a slight increase in PEUE by 43.8%. Additionally, W. trilobata individuals grown in elevated CO₂ increased energy allocation towards stems. Statistic analysis revealed significant associations between growth characteristics (relative growth rate and biomass) and energetic properties (CC and PEUE), suggesting the greater growth stimulation in invasive species could be partly explained by its specific energetic properties in elevated CO₂ concentration. The invasive species showed a greater increase in energy-use efficiency under elevated CO₂, which consequently facilitated its growth. It might be a physiological mechanism promoting success of invasion with ongoing increase in atmospheric CO₂ concentration.     

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.     

Seedlings growth and antioxidative enzymes activities in leaves under heavy metal stress differ between two desert plants: a perennial (<Emphasis Type="Italic">Peganum harmala</Emphasis>) and an annual (<Emphasis Type="Italic">Halogeton glomeratus</Emphasis>) grass

The present study showed the toxicity caused by heavy metal and its detoxification responses in two desert plants: perennial Peganum harmala and annual Halogeton glomeratus. In pot experiments, 1-month-old seedlings were grown under control and three levels of combined heavy metal stress. Seedling growth as well as heavy metal accumulation, antioxidative enzymes [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)] activities and the contents of malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) in leaves was examined after 2 months of heavy metal exposure. Compared with H. glomeratus, growth of P. harmala was more severely inhibited. In leaves, the heavy metal accumulation pattern in both the plants was dose-dependent, being more in H. glomeratus. H. glomeratus exhibited a typical antioxidative defense mechanism, as evidenced by the elevated activities of all the three enzymes tested. P. harmala exhibited a different enzyme response pattern, with a significant reduction in CAT activity, and elevated SOD and APX activities, but significantly elevated APX activity was only at the lowest heavy metal concentration. MDA and H₂O₂ contents were significantly enhanced in leaves of heavy metal-treated P. harmala, but in H. glomeratus were elevated only at the highest heavy metal treatment. These results indicated that H. glomeratus had a greater capacity than P. harmala to adapt to oxidative stress caused by heavy metal stress, and antioxidative defense in H. glomeratus might play an important role in heavy metal tolerance.     

Prolonged Growth of Young Spruce (<Emphasis Type="Italic">Picea koraiensis</Emphasis> Nakai) Plants at Double Atmospheric CO<Subscript>2</Subscript> Concentration Stimulates the Preferential Growth of Thick Roots

Two-year-old young spruce (Picea koraiensis Nakai) plants were grown in a climatic chamber during three summer months at double atmospheric CO₂ concentration, sufficient content of soil inorganic nitrogen, and diurnal variation of temperature and illuminance, which simulate natural growth conditions. The control plants were grown in another climatic chamber under the same conditions, but at atmospheric CO₂ concentration (350 ppm). CO₂ exchange was measured with a Li-Cor 6400 infra-red gas analyzer in attached leaves placed in a climatic chamber in the morning under growth conditions and saturating light 1200 μE/(m² s) in June, July, and August. In addition, dry weights of needles, leafless shoot parts of plant, fraction of thick (more than 0.5 mm in diameter) and thin (less than 0.5 mm in diameter) roots were recorded. The data were used to plot CO₂ exchange rates as a function of carbon dioxide concentration and to calculate the increment of shoot and root phytomass. The maximum gas exchange rates in the treated and control plants similarly depended on CO₂ concentration. The slope of the CO₂ dependence curve, which corresponded to the kinetic characteristic V _m /K _M of photosynthetic carboxylation, increased monotonically during the experiment. To the end of observation period, the proportion of thick roots in plant phytomass significantly increased in the plants grown at double atmospheric CO₂ concentration, as compared to the control plants. Thus, the increase in the rate of photosynthetic gas exchange in plants grown for three months at double atmospheric CO₂ concentration was only due to the increase in CO₂, the substrate of Rubisco carboxylation activity. We found no differences in the CO₂ characteristic for Rubisco between the treated and control plants. The ratio of needle to thin roots in the treated and control plants was similar and did not change during the experiment. The excess of photoassimilates in the treated, as compared to the control plants, was preferentially used for thick root growth. This result shows that photosynthesis in young spruce forests can deposit excess atmospheric CO₂ in the soil horizon in the form of thick root phytomass. __________ Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 741–746. Original Russian Text Copyright ? 2005 by Mao, Y.-J. Wang, Zhu, X.-W. Wang, Sun, Zhou, Voronin.     

Elevated CO<Subscript>2</Subscript> ameliorated oxidative stress induced by elevated O<Subscript>3</Subscript> in <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Using open top chambers, the effects of elevated O₃ (80 nmol mol⁻¹) and elevated CO₂ (700 μmol mol⁻¹), alone and in combination, were studied on young trees of Quercus mongolica. The results showed that elevated O₃ increased malondialdehyde content and decreased photosynthetic rate after 45 days of exposure, and prolonged exposure (105 days) induced significant increase in electrolyte leakage and reduction of chlorophyll content. All these changes were alleviated by elevated CO₂, indicating that oxidative stress on cell membrane and photosynthesis was ameliorated. After 45 days of exposure, elevated O₃ stimulated activities of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11), but the stimulation was dampened under elevated CO₂ exposure. Furthermore, ascorbate (AsA) and total phenolics contents were not higher in the combined gas treatment than those in elevated O₃ treatment. It indicates that the protective effect of elevated CO₂ against O₃ stress was achieved hardly by enhancing ROS scavenging ability after 45 days of exposure. After 105 days of exposure, elevated O₃ significantly decreased activities of SOD, catalase (CAT, EC 1.11.1.6) and APX and AsA content. Elevated CO₂ suppressed the O₃-induced decrease, which could ameliorate the oxidative stress in some extent. In addition, elevated CO₂ increased total phenolics content in the leaves both under ambient O₃ and elevated O₃ exposure, which might contribute to the protection against O₃-induced oxidative stress as well.     

Combination of elevated CO<Subscript>2</Subscript> concentration and elevated temperature and elevated temperature only promote photosynthesis of <Emphasis Type="Italic">Quercus mongolica</Emphasis> seedlings

One-year-old oak (Quercus mongolica Fisch.) seedlings were grown in growth chambers for 30 days to investigate the effects of the combination of elevated CO₂ concentration ([CO₂], 700 μmol/mol) and temperature (ambient T + 4°C) and only elevated temperature (ambient T +4°C) on leaf gas exchange, chlorophyll a fluorescence, and chlorophyll content. In the growth chambers, natural conditions of the Maoershan mountain regions of Heilongjiang Province (45–46°N, 127–128°E) of China for the average growth season were simulated. The results showed that the maximum net photosynthetic rate (P _Nmax) was ≈ 1.64 times greater at elevated temperature than at ambient temperature. The irradiance saturation point (I _s), apparent quantum yield (AQY), maximum photosystem II efficiency (F _v/F _m), and chlorophyll content significantly increased, while irradiance compensation point (I _c) was not affected by elevated temperature. The combination of elevated [CO₂] and temperature also significantly increased P _Nmax by approximately 34% but much lower than that under elevated temperature only. In the case of factor combination, dark respiration (R _d), I _c, F _v/F _m, and total chlorophyll content increased significantly, while I _s and AQY were not affected. Moreover, under elevated [CO₂] and temperature, R _d and I _c, F _v/F _m were significantly higher than under elevated temperature only. The results indicated that the combination of elevated [CO₂] and temperature expected in connection with the further global climate change may affect carbon storage of the coenotype of Q. mongolica in this region of China. This text was submitted by the authors in English.     

Elevated CO<Subscript>2</Subscript> influences host plant defense response in chickpea against <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

Global atmospheric concentration of CO₂ is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO₂ on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteen-day-old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO₂. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO₂ concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO₂ than in plants kept under ambient conditions. The H. armigera-infested plants had higher H₂O₂ content; amounts of oxalic and malic acids were greater at 750 ppm CO₂ than at 350 ppm CO₂. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO₂. This information will be useful for understanding effects of increased levels of CO₂ on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change.     

Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Phytoextraction of cadmium and physiological changes in <Emphasis Type="Italic">Solanum nigrum</Emphasis> as a novel cadmium hyperaccumulator

It is still difficult to fully understand the physiological, biochemical, and molecular mechanisms involved in metal hyperaccumulation and how plants adjust to an adverse environment. Solanum nigrum L. is a novel Cd-hyperaccumulator, which antioxidant defense and photosynthetic CO₂ fixation were investigated in this study. The results showed that the elevated heavy metal concentration, inhibiting S. nigrum growth, was accompanied by a decrease in the photosynthetic CO₂ fixation. The presence of heavy metal in soil led to disturbances in the antioxidant responses, especially in superoxide dismutase, malondialdehyde, phytochelatins, and total acid-soluble thiols, which indices in S. nigrum were significantly correlated with the elevated heavy metal concentration. Whereas peroxidase activity in S. nigrum showed a slight difference and irregular change, reduced glutathione significantly decreased with increasing culturing time and elevated Cd concentration. Thus, the manipulation of antioxidant enzyme activities increases tolerance, thereby potentially increasing the uptake capacity of an organism.     

High-Level Expression of Heme-Dependent Catalase Gene <Emphasis Type="Italic">katA</Emphasis> from <Emphasis Type="Italic">Lactobacillus Sakei</Emphasis> Protects <Emphasis Type="Italic">Lactobacillus Rhamnosus</Emphasis> from Oxidative Stress

Lactic acid bacteria (LAB) are generally sensitive to hydrogen peroxide (H₂O₂), Lactobacillus sakei YSI8 is one of the very few LAB strains able to degrade H₂O₂ through the action of a heme-dependent catalase. Lactobacillus rhamnosus strains are very important probiotic starter cultures in meat product fermentation, but they are deficient in catalase. In this study, the effect of heterologous expression of L. sakei catalase gene katA in L. rhamnosus on its oxidative stress resistance was tested. The recombinant L. rhamnosus AS 1.2466 was able to decompose H₂O₂ and the catalase activity reached 2.85 μmol H₂O₂/min/10⁸ c.f.u. Furthermore, the expression of the katA gene in L. rhamnosus conferred enhanced oxidative resistance on the host. The survival ratios after short-term H₂O₂ challenge were increased 600 and 10⁴-fold at exponential and stationary phase, respectively. Further, viable cells were 100-fold higher in long-term aerated cultures. Simulation experiment demonstrated that both growth and catalase activity of recombinant L. rhamnosus displayed high stability under environmental conditions similar to those encountered during sausage fermentation.     

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.     

Comparison of tolerance of <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Vigna radiata</Emphasis> to cadmium

The effect of different cadmium concentrations (6–120 μM) on Hill reaction activity (HRA) of isolated chloroplasts, contents of chlorophylls (Chls) and carotenoids (Cars), and Cd uptake and accumulation in plant organs of Indian mustard (Brassica juncea L. cv. Vitasso) and mung bean [Vigna radiata (L.) Wilczek] were determined. The Cd stress inhibited photochemical activity of isolated chloroplasts of both species and in both tested developmental stages. On the basis of EC₅₀ values, the mung bean showed a higher sensitivity to Cd treatment than Indian mustard. The higher sensitivity of both species was determined in the earlier than in the older developmental stage. The leaves of Cd-treated plants possessed lower contents of Chls and Cars in both species and the negative effect increased with Cd concentration. A difference between species was also found in Cd uptake and accumulation. In both species, Cd was accumulated more in roots than in shoots, with higher accumulation in Indian mustard than in mung bean.     

Phototropic H<Subscript>2</Subscript> production by a newly isolated strain of <Emphasis Type="Italic">Rhodopseudomonas</Emphasis><Emphasis Type="Italic">palustris</Emphasis>

Rhodopseudomonas palustris TN1 was isolated from Songkhla Lake, Thailand. It phototrophically generates H₂ from the predominant volatile fatty acids (VFAs) produced from microbial dark-fermentations of palm oil milling effluent; yields from 20 mM butyrate, acetate and propionate were 4.7, 2.5, and 1.7 mol H₂ mol VFA⁻¹ with light efficiencies of 1.8, 1, and 0.2%, respectively. Optimum conditions were pH 7 and 3000 lux, although production was reduced by only 33% at 1000 lux. CO₂ evolution never exceeded 9 mmol mol VFA⁻¹.