The effect of elevated CO2 concentration on leaf chlorophyll and nitrogen contents in rice during post-flowering phases

The effect of elevated CO₂ concentration (CE) on leaf chlorophyll (Chl) and nitrogen (N) contents and photosynthetic rate (P_N) was evaluated during the post-flowering stages of rice grown at CE (570 ± 50 μmol mol⁻¹) in open top chamber (OTC), at ambient CO₂ concentration (∼ 365 μmol mol⁻¹) in OTC and at open field. Thirty-five day old seedlings were transplanted in OTCs or in field and allowed to grow till maturity. Chl and N contents were highest at the time of flowering and thereafter it started to decline. The rate of decline in Chl and N contents was faster in plants grown under CE mostly in later part of growth. Irrespective of treatment difference, flag leaf contained the highest amount of Chl and N than penultimate and third leaf. The higher P_N was observed in leaves under CE than in the leaves in other two growing conditions. Considering growth stage, P_N was the highest at flowering which reduced at the later part of growth due to degradation of Chl and N content of the leaf. Under CE it was 40.02 μmol m⁻² s⁻¹ at flowering and it reduced to only 14.77 μmol m⁻² s⁻¹ at maturity stage. The beneficial effect of CE in increasing leaf P_N may be maintained by applying extra dose of nitrogen at the later stages of plant growth.     

Impact of CO2 Enrichment and Variable Nitrogen Supplies on Composition and Partitioning of Essential Nutrients of Wheat

This study was conducted to determine effects of nitrogen supply (75 and 150 kg(N) ha⁻¹) and CO₂ enrichment on partitioning of macro and micro nutrients in wheat (Triticum aestivum L. cv. HD-2285). Plants were grown from seedling emergence to maturity inside open top chambers under ambient CO₂ (CA, 350 ± 50 μmol mol⁻¹) and elevated CO₂ (CE, 600 ± 50 μmol mol⁻¹). Leaves, stems and roots of the same physiological age were analyzed for carbon, nitrogen, calcium, copper, iron, zinc and manganese content at 40, 60 and 90 d after germination. C, Cu, Mn and Zn content was higher in the stem, leaves and roots on dry mass basis under CE than CA. However, N and Fe contents decreased in CE grown plants. Ca content was unaffected due to CE and variable N supplies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen and carbon partitioning in soybean under variable nitrogen supplies and acclimation to the prolonged action of elevated CO2

This study was conducted to determine reciprocal effects of low to high doses of nitrogenous fertilizer (N₃₀, N₄₀, N₅₀, N₆₀ and N₇₀ — 30, 40, 50, 60 and 70 kg ha⁻¹ respectively) and CO₂ enriched environment on C and N partitioning in soybean (Glycine max (L.) Merril cv JS-335). Plants were grown from seedling emergence to maturity inside open top chambers under ambient, AC (350±50 mol mol⁻¹) and elevated, EC (600±50 mol mol⁻¹) CO₂ and analyzed at seedling, vegetative, flowering, pod setting and maturity stages. Soybean responded to both CO₂ enrichment and N supply. Leaves, stem and root reserves at different growth stages were analyzed for total C and N contents. Consistent increase in the C contents of the leaf, stem and root was observed under EC than in AC. N contents in the different plant parts were found to be decreased under EC-grown plants specially at seedling and vegetative stage despite providing N doses to the soil. Significant increase observed for C to N dry mass ratio under EC in the root, stems and leaves at seedling and vegetative stage was decreased in the middle and later growth stages possibly due to combined impact of N doses to the soil and increased N₂ fixing activities due to EC conditions. Critical analysis of our findings reveals that the composition and partitioning of C and N of soybean under variable rates of N supply and CO₂ enrichment alter according to need under altered metabolic process. These changes eventually may lead to alteration in uptake of not only N but other essential nutrients also under changing atmosphere.     

Elevated CO2 enhances photosynthetic efficiency,ion uptake and antioxidant activity of Gynura bicolor DC. grown in a porous‐tube nutrient delivery system under simulated microgravity

It is well known that plants can grow under space conditions, however, perturbations of many biological phenomena have been highlighted due to the effect of altered gravity and its possible interaction with other factors (e.g., CO₂, ion radiation, etc. Our aim was to test whether elevated CO₂ could provide ‘protection’ to Gynura bicolor against the damaging effects of simulated microgravity (SM) on photosynthesis, ion uptake and antioxidant activity. As compared to G. bicolor grown in ambient CO₂ with no SM (ACO₂), growth and yield of the plants increased under elevated ambient CO₂ with no SM (ECO₂) and decreased under ACO₂+SM, whereas there was no significant effect on ECO₂+SM. Reductions in the content of Chl a, carotenoids and Chl a+b were 17.9%, 20.7% and 17.9% under ACO₂+SM, respectively, but under ECO₂ there was a significant effect on all photosynthetic pigments except Chl b, compared to ACO₂. Photosynthesis was improved under ECO₂ with SM and such an improvement was associated with improved water use efficiency and instantaneous carboxylation efficiency. Furthermore, SM caused a reduction in ion absorption rate, except for Ca²⁺, while ECO₂ increased the uptake rate. Finally, the activity of SOD, POD and the content of MDA and H₂O₂ were enhanced under SM treatments and were highest in ACO₂+SM. In contrast, T‐AOC activity and GSH content significantly declined in ACO₂+SM compared to other treatments. These results suggest that ACO₂ is not sufficient to counteract SM impact, but the increase is usually caused by improvement in CO₂ nutrition in ECO₂+SM in comparison with ACO₂+SM.     

Short-term effect of elevated CO2 concentration and high irradiance on the antioxidant enzymes in bean plants

The effect of short-term exposure to elevated CO₂ concentration and high irradiance on the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (GPX) and catalase (CAT), and on the extent of the lipid peroxidation was studied in bean (Phaseolus vulgaris L.) plants. Plants were exposed for 4 d (8 h a day) to irradiance of 100 (LI) or 1000 (HI) μmol m⁻² s⁻¹ at ambient (CA, 350 μmol mol⁻¹) or elevated (CE, 1300 μmol mol⁻¹) CO₂ concentration. Four-day exposure to CE increased the leaf dry mass in HI plants and RuBPC activity and chlorophyll content in LI plants. Total soluble protein content, leaf dry matter and RuBPC activity were higher in HI than in LI plants, although the HI and CE increased the contents of malonyldialdehyde and H₂O₂. Under CA, exposure to HI increased the activity of APX and decreased the total SOD activity. Under CE, HI treatment also activated APX and led to reduction of both, SOD and GPX, enzymes activities. CE considerably reduced the CAT activity at both irradiances, possibly due to suppressed rate of photorespiration under CE conditions.     

Response of Photosynthetic Apparatus of Spring Barley (Hordeum vulgare L.) to Combined Effect of Elevated CO2 Concentration and Different Growth Irradiance

The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO₂] [700 μmol (CO₂) mol⁻¹; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO₂] [350 μmol (CO₂) mol⁻¹; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m⁻² s⁻¹ (PPFD₇₃₀), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD₇₃₀ barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as F_V/F_M) for EC plants grown at 730 and 1 200 μmol m⁻² s⁻¹ in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD₇₃₀) to the photoinactivation of PS2. This revised version was published online in August 2006 with corrections to the Cover Date.     

A coupled model of stomatal conductance and photosynthesis for winter wheat

The model couples stomatal conductance (g _s) and net photosynthetic rate (P _N) describing not only part of the curve up to and including saturation irradiance (I _max), but also the range above the saturation irradiance. Maximum stomatal conductance (g _smax) and I _max can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum P _N (P _max) at 600 μmol mol⁻¹ was more than at 350 μmol mol⁻¹ under the same leaf temperature, which can not be explained by the stomatal closure at high CO₂ concentration because g _smax at 600 μmol mol⁻¹ was less than at 350 μmol mol⁻¹. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 μmol mol⁻¹ both P _N and g _s almost synchronously reached the maximum values at about 1 600 μmol m⁻² s⁻¹. At 25 °C and 600 μmol mol⁻¹ the I _max corresponding to P _max and g _smax was 2 080 and 1 575 μmol m⁻² s⁻¹, respectively.     

The effects of parental CO2 environment on seed quality and subsequent seedling performance in Bromusrubens

Seeds were collected and compared from parent plants of Bromusrubens L. (Poaceae), an exotic Mojave Desert annual grass, grown in ambient (360 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ to determine if parental CO₂ growth conditions affected seed quality. Performance of seeds developed on the above plants was evaluated to determine the influence of parental CO₂ growth conditions on germination, growth rate, and leaf production. Seeds of B. rubens developed on parents grown in elevated CO₂ had a larger pericarp surface area, higher C:N ratio, and less total mass than ambient-developed seeds. Parental CO₂ environment did not have an effect on germination percentage or mean germination time, as determined by radicle emergence. Seedlings from elevated-CO₂-developed seeds had a reduced relative growth rate and achieved smaller final mass over the same growth period. Elevated-CO₂-developed seeds had smaller seed reserves than ambient seeds, as determined by growing seedlings in sterile media and monitoring senescence. It appears that increased seed C:N ratios associated with plants grown under elevated CO₂ may have a major effect on seed quality (morphology, nutrition) and seedling performance (e.g., growth rate and leaf production). Since the invasive success of B. rubens is primarily due to its ability to rapidly germinate, increase leaf area and maintain a relatively high growth rate compared to native annuals and perennial grasses, reductions in seed quality and seedling performance in elevated CO₂ may have significant impacts on future community composition in the Mojave Desert. Received: 11 April 1997 / Accepted: 20 November 1997     

Is photosynthetic acclimation to free-air CO<Subscript>2</Subscript> enrichment (FACE) related to a strong competition for the assimilatory power between carbon assimilation and nitrogen assimilation in rice leaf?

Net photosynthetic rate (P _N) of leaves grown under free-air CO₂ enriched condition (FACE, about 200 μmol mol⁻¹ above ambient air) was significantly lower than P _N of leaves grown at ambient CO₂ concentration (AC) when measured at CO₂ concentration of 580 μmol mol⁻¹. This difference was found in rice plants grown at normal nitrogen supply (25 g m⁻²; NN-plants) but not in plants grown at low nitrogen supply (15 g m⁻²; LN-plants). Namely, photosynthetic acclimation to FACE was observed in NN-plants but not in LN-plants. Different from the above results measured in a period of continuous sunny days, such photosynthetic acclimation occurred in NN-plants, however, it was also observed in LN-plants when P _N was measured before noon of the first sunny day after rain. Hence strong competition for the assimilatory power between nitrogen (N) and carbon (C) assimilations induced by an excessive N supply may lead to the photosynthetic acclimation to FACE in NN-plants. The hypothesis is supported by the following facts: FACE induced significant decrease in both apparent photosynthetic quantum yield (Φ_c) and ribulose-1,5-bisphosphate (RuBP) content in NN-plants but not in LN-plants.     

Photosystem 2 activity of <Emphasis Type="Italic">Citrus volkameriana</Emphasis> (L.) leaves as affected by Mn nutrition and irradiance

Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 μM Mn (Mn₀, Mn₂, Mn₁₄, Mn₉₈, and Mn₆₈₆, respectively). To adequately investigate the combined effects of Mn nutrition and irradiance on photosystem 2 (PS2) activity, irradiance response curves for electron transport rate (ETR), nonphotochemical quenching (q_N), photochemical quenching (q_P), and real photochemical efficiency of PS2 (Φ_PS2) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1 211, 1 911, and 3 111 μmol m⁻² s⁻¹, I₆₆ to I₃₁₁₁, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn₆₈₆) compared to Mn₀; its highest values were recorded in the treatments Mn₂-Mn₉₈. However, ETR and Φ_PS2 values were significantly lower under Mn₀ compared to the other Mn treatments, when plants were exposed to irradiances ≥96 μmol m⁻² s⁻¹. Furthermore, Mn₀ plants had significantly higher values of q_N and lower values of q_P at irradiances ≤226 and ≥336 μmol m⁻² s⁻¹, respectively, than those grown under Mn₂-Mn₆₈₆. Irrespective of Mn treatment, the values of Φ_PS2 and q_N decreased, while those of q_P increased progressively by increasing irradiance from I₁₃₆ to I₃₁₁₁. Finally, Mn₂-Mn₉₈ plants were less sensitive to photoinhibition of photosynthesis (≥811 μmol m⁻² s⁻¹) than the Mn₆₈₆ (≥536 μmol m⁻² s⁻¹) and Mn₀ (≥336 μmol m⁻² s⁻¹) ones.     

Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes

To study whether responses of antioxidative enzymes to enhanced atmospheric CO₂ concentrations are affected by plant nutrition, the activities of superoxide dismutase, catalase and peroxidase were investigated in leaves of 3-year-old beech trees grown with low (0.1 × optimum), intermediate (0.5 × optimum) and high (2 × optimum) nutrient supply rates in open-top chambers at either ambient (～ 355 μmol mol^?1) or elevated (700 μmol mol^?1) CO₂ concentrations. These treatments resulted in foliar C/N ratios of about 20 in the presence of high and > 30 in the presence of low nutrient supply rates. Pigment and malon-dialdehyde contents were determined to assess plant stress levels. Low nutrient supply rates caused pigment loss, whereas elevated CO₂ had no effect on pigmentation. Guaiacol peroxidase activities did not respond to either CO₂ or nutrient treatment. Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO₂. Superoxidase dismutase activity was affected by both nutrient supply and CO₂ concentration. In leaves from trees grown with the high-nutrient treatment, superoxide dismutase activity was low irrespective of CO₂ concentration. In chlorotic leaves, superoxide dismutase activity was increased, suggesting an enhanced need for detoxification of reactive oxygen species. Leaves from plants grown under elevated CO₂ with medium nutrient supply rates showed decreased malondialdehyde contents and superoxide dismutase activities. This suggests that the intrinsic oxidative stress of leaves was decreased under these conditions. These results imply that intrinsic oxidative stress is modulated by the balance between N and C assimilation.     

The impact of elevated CO2 on growth and photosynthesis in Agrostis canina L. ssp. monteluccii adapted to contrasting atmospheric CO2 concentrations

 The aim of this study was to characterise growth and photosynthetic capacity in plants adapted to long-term contrasting atmospheric CO₂ concentrations (C _a). Seeds of Agrostis canina L. ssp. monteluccii were collected from a natural CO₂ transect in central-western Italy and plants grown in controlled environment chambers at both ambient and elevated CO₂ (350 and 700 μmol mol⁻¹) in nutrient-rich soil. Seasonal mean C _a at the source of the plant material ranged from 610 to 451 μmol CO₂ mol⁻¹, derived from C₄ leaf stable carbon isotope discrimination (δ¹³C). Under chamber conditions, CO₂ enrichment stimulated the growth of all populations. However, plants originating from elevated C _a exhibited higher initial relative growth rates (RGRs) irrespective of chamber CO₂ concentrations and a positive relationship was found between RGR and C _a at the seed source. Seed weight was positively correlated with C _a, but differences in seed weight were found to explain no more than 34% of the variation in RGRs at elevated CO₂. Longer-term experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 μmol CO₂ mol⁻¹) indicated that differences in growth between populations were maintained when plants were grown at both 350 and 700 μmol CO₂ mol⁻¹. Analysis of leaf material revealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO₂, with plants originating from high C _a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO₂ saturated rates of photosynthesis and carboxylation efficiency between populations or with CO₂ treatment. Moreover, SDS-PAGE/ LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rubisco content between populations or CO₂ treatments. These findings suggest that long-term adaptation to growth at elevated CO₂ may be associated with a potential for increased growth, but this does not appear to be linked with differences in the intrinsic capacity for photosynthesis. Received: 16 August 1996 / Accepted: 19 October 1996     

Photosynthesis and photoinhibition in two differently coloured varieties of <Emphasis Type="Italic">Oxalis triangularis</Emphasis> — the effect of anthocyanin content

The purpose of this study was to clarify effects of anthocyanins on photosynthesis and photoinhibition in green and red leaves of Oxalis triangularis. Gas analysis indicated that green plants had the highest apparent quantum yield for CO₂ assimilation [0.051 vs. 0.031 μmol(CO₂) μmol⁻¹(photon)] and the highest maximum photosynthesis [10.07 vs. 7.24 μmol(CO₂) m⁻² s⁻¹], while fluorescence measurements indicated that red plants had the highest PSII quantum yield [0.200 vs. 0.143 μmol(e⁻) μmol⁻¹(photon)] and ETR_max [66.27 vs. 44.34 μmol(e⁻) m⁻² s⁻¹]. Red plants had high contents of anthocyanins [20.11 mg g⁻¹(DM)], while green plants had low and undetectable levels of anthocyanin. Red plants also had statistically significantly (0.05>p>0.01) lower contents of xanthophyll cycle components [0.63 vs. 0.76 mg g⁻¹(DM)] and higher activities of the reactive oxygen scavenging enzyme ascorbate peroxidase [41.2 vs. 10.0 nkat g⁻¹(DM)]. Anthocyanins act as a sunscreen, protecting the chloroplasts from high light intensities. This shading effect causes a lower photosynthetic CO₂ assimilation in red plants compared to green plants, but a higher quantum efficiency of photosystem II (PSII). Anthocyanins contribute to photoprotection, compensating for lower xanthophyll content in red plants, and red plants are less photoinhibited than green plants, as illustrated by the F_v/F_m ratio.     

Effects of atmospheric CO2 enrichment and root restriction on leaf gas exchange and growth of banana (Musa)

The effects of atmospheric CO₂ enrichment and root restriction on photosynthetic characteristics and growth of banana (Musa sp. AAA cv. Gros Michel) plants were investigated. Plants were grown aeroponically in root chambers in controlled environment glasshouse rooms at CO₂ concentrations of 350 or 1 000 μmol CO₂ mol^-1. At each CO₂ concentration, plants were grown in large (2001) root chambers that did not restrict root growth or in small (20 1) root chambers that restricted root growth. Plants grown at 350 μmol CO₂ mol^-1 generally had a higher carboxylation efficiency than plants grown at 1 000 μmol CO₂ mol^-1 although actual net CO₂ assimilation (A) was higher at the higher ambient CO₂ concentration due to increased intercellular CO₂ concentrations (C_i resulting from CO₂ enrichment. Thus, plants grown at 1 000 μmol CO₂ mol^-1 accumulated more leaf area and dry weight than plants grown at 350 μmol CO₂ mol^-1. Plants grown in the large root chambers were more photosynthetically efficient than plants grown in the small root chambers. At 350 μmol CO₂ mol^-1, leaf area and dry weights of plant organs were generally greater for plants in the large root chambers compared to those in the small root chambers. Atmospheric CO₂ enrichment may have compensated for the effects of root restriction on plant growth since at 1 000 μmol CO₂ mol^-1 there was generally no effect of root chamber size on plant dry weight.     

Growth of In vitro banana (Musa SPP.) shoots under photomixotrophic and photoautotrophic conditions

Summary In vitro banana (Musa spp.) shoots were cultured under photomixotrophic (30 gl⁻¹ sucrose and 0.2 h⁻¹ number of air exchanges of culture vessels) and photoautotrophic (0 gl⁻¹ sucrose and 3.9 h⁻¹ number of air exchanges) conditions for 28 d in 370 cm³ Magenta boxes (GA7-type) containing 70 ml of half-strength Murashige and Skoog (MS) medium with 22.2 μM N⁶-benzyladenine (BA). The effects of varying CO₂ concentration (475 or 1340 μmol mol⁻¹) and light intensity (photosynthetic photon flux (PPF) of 100 or 200 μmol m⁻² s⁻¹) were investigated. Fresh and dry weights of banana shoots grown photomixotrophically were significantly greater on day 28 than those grown photoautotrophically. Photoautorophic shoots had a larger number of unfolded leaves and greater leaf area than photomixotrophic plants by days 14 and 28, regardless of CO₂ concentration. The shoot fresh and dry weights on day 14 in photoautotrophic conditions were significantly greater at PPF of 200 μmol m⁻² s⁻¹ than at 100 μmol m⁻² s⁻¹. The increase in net photosynthetic rate of photoautotrophic banana shoots was significant compared with photomixotrophic shoots. The multiplication ratio of in vitro banana shoots grown photoautotrophically in a 28-d culture period was the greatest at 100 μmol m⁻² s⁻¹ PPF and 475 μmol mol⁻¹ CO₂.     

Water relations in Norway spruce trees growing at ambient and elevated CO2 concentrations

Water relations were studied in Norway spruce [Picea abies (L.) Karst.] trees grown at ambient (AC, 350 μmol mol⁻¹) and elevated (EC, 700 μmol mol⁻¹) CO₂ concentrations under temperate water stress. The results suggested that both crown position and variability in atmospheric CO₂ concentration are responsible for different patterns of crown water relations. Mean hourly sap flux density (FSA) showed higher values in upper crown position in comparison with the whole crown in both AC and EC treatments. Mean soil-to-leaf hydraulic conductance (G_Tsa) was 1.4 times higher for the upper crown than that calculated across the whole crown for the trees in AC. However, G_Tsa did not vary significantly with crown position in EC trees, suggesting that elevated CO₂ may mitigate differences in hydraulic supply for different canopy layers. The trees in EC treatment exhibited significantly higher values of F_SA measured on the whole crown level and slightly higher soil water content compared to AC treatment, suggesting more economical use of soil water and therefore an advantage under water-limited conditions.     

Effects of elevated CO<Subscript>2</Subscript> and/or O<Subscript>3</Subscript> on hormone IAA in needles of Chinese pine

This study examined the effects of season-long exposure of Chinese pine (Pinus tabulaeformis) to elevated carbon dioxide (CO₂) and/or ozone (O₃) on indole-3-acetic acid (IAA) content, activities of IAA oxidase (IAAO) and peroxidase (POD) in needles. Trees grown in open-top chambers (OTC) were exposed to control (ambient O₃, 55 nmol mol⁻¹ + ambient CO₂, 350 μmol mol⁻¹, CK), elevated CO₂ (ambient O₃ + high CO₂, 700 μmol mol⁻¹, EC) and elevated O₃ (high O₃, 80 ± 8 nmol mol⁻¹ + ambient CO₂, EO) OTCs from 1 June to 30 September. Plants grown in elevated CO₂ OTC had a growth increase of axial shoot and needle length, compared to control, by 20% and 10% respectively, while the growth in elevated O₃ OTC was 43% and 7% less respectively, than control. An increase in IAA content and POD activity and decrease in IAAO activity were observed in trees exposed to elevated CO₂ concentration compared with control. Elevated O₃ decreased IAA content and had no significant effect on IAAO activity, but significantly increased POD activity. When trees pre-exposed to elevated CO₂ were transferred to elevated O₃ (EC–EO) or trees pre-exposed to elevated O₃ were transferred to elevated CO₂ (EO–EC), IAA content was lower while IAAO activity was higher than that transferred to CK (EC–CK or EO–CK), the change in IAA content was also related to IAAO activity. The results indicated that IAAO and POD activities in Chinese pine needles may be affected by the changes in the atmospheric environment, resulting in the change of IAA metabolism which in turn may cause changes in Chinese pine’s growth. An erratum to this article can be found at     

The effect of elevated CO2 concentration and nutrient supply on carbon-based plant secondary metabolites in Pinus sylvestris L.

This study investigated changes in carbon-based plant secondary metabolite concentrations in the needles of Pinus sylvestris saplings, in response to long-term elevation of atmospheric CO₂, at two rates of nutrient supply. Experimental trees were grown for 3 years in eight open-top chambers (OTCs), four of which were maintained at ambient (∼350 μmol mol⁻¹) and four at elevated (700 μmol mol⁻¹) CO₂ concentrations, plus four open air control plots. Within each of these treatments, plants received either high (7.0 g N m⁻² year⁻¹ added) or low (no nutrients added) rates of nutrient supply for two years. Needles from lateral branches were analysed chemically for concentrations of condensed tannins and monoterpenes. Biochemical determinations of cellulase digestibility and protein precipitating capacity of their phenolic extracts were made because of their potential of importance in ecological interactions between pine and other organisms including herbivores and decomposers. Elevated CO₂ concentration caused an increase (P<0.05) in dry mass per needle, tree height and the concentration of the monoterpene α-pinene, but there were no direct effects of CO₂ concentration on any of the other chemical measurements made. High nutrient availability increased cellulase digestibility of pine needles. There was a significant negative effect of the OTCs on protein precipitating capacity of the needle extracts in comparison to the open-air controls. Results suggest that predicted changes in atmospheric CO₂ concentration will be insufficient to produce large changes in the concentration of condensed tannins and monoterpenes in Scots pine. Processes which are influenced by these compounds, such as decomposition and herbivore food selection, along with their effects on ecosystem functioning, are therefore unlikely to be directly affected through changes in these secondary metabolites. Received: 20 October 1997 / Accepted: 28 February 1998     

Intrinsic changes in photosynthetic parameters of carrot leaves under increasing CO<Subscript>2</Subscript> concentrations and soil moisture regimes

A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses of 30-d-old carrot seedlings to the combined effects of CO₂ concentration (50–1 050 μmol mol⁻¹) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola model. The estimated parameters were compared for effects of moisture deficit and elevated CO₂ concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC. Maximum net photosynthetic rate (P _Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced P _Nmax by nearly 85 % compared to controls. Dark respiration rate (R _D) showed no consistent response to moisture deficit. The CO₂ compensation concentration (Γ) was 324 μmol mol⁻¹ for −75 kPa and ranged 63–93 μmol mol⁻¹ for other moisture regimes. Interaction between moisture deficit and EC was noticed for P _N, ratio of intercellular and ambient CO₂ concentration (C _i/C _a), stomatal conductance (g _s ), and transpiration rate (E). P _N was maximum and C _i/C _a was minimum at −30 kPa moisture deficit and at C _a of 350 μmol mol⁻¹. The g _s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P _N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture deficits.     

Infection with the parasitic angiosperm Striga hermonthica influences the response of the C3 cereal Oryza sativa to elevated CO2

Upland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol^?1) and elevated (700 μmol mol^?1) CO₂ in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO₂ alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO₂ was 35% that of uninfected, control plants, while at elevated CO₂, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO₂ supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO₂. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO₂. There were significant CO₂ and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO₂] (A/C_i curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO₂ had significantly lower CO₂ saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO₂‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO₂, but had no impact on photosynthesis of hosts grown at ambient CO₂. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO₂ had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO₂. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO₂ or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO₂ concentrations. These results demonstrate that elevated CO₂ concentrations can alleviate the impact of infection with Striga on the growth of C₃ hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO₂.