Reduction of leaf photosynthesis and transpiration rates of potato plants by second-stage juveniles of Globodera pallida

Abstract. Net photosynthesis and transpiration rates of potato plants, grown in pots in the greenhouse, were measured at various light irradiances and ambient CO₂ concentrations, 3d after inoculation with second stage juveniles of Globodera pallida. Gas exchange rates, both in darkness and in light, and the initial light use efficiency were strongly reduced by nematodes. Stomatal conductance of infected plants was lower than that of control plants and showed little response to decreasing ambient CO₂ concentration. The maximum internal CO₂ concentration of infected plants was lower than that of control plants. Globodera pallida reduced photosynthesis also by apparent non-stomatal effects.
The effects of G. pallida on gas exchange rates are similar to the effects of abscisic acid in the transpiration stream and of abiotic stresses in the root environment. Apparently, there is a general response of plant roots to adverse conditions. The reduction of photosynthesis may be an important factor in yield reduction by potato cyst nematodes.     

Elevated CO2 and ozone reduce nitrogen acquisition by Pinus halepensis from its mycorrhizal symbiont

The effects of 700 μmol mol⁻¹ CO₂ and 200 nmol mol⁻¹ ozone on photosynthesis in Pinus halepensis seedlings and on N translocation from its mycorrhizal symbiont, Paxillus involutus, were studied under nutrient-poor conditions. After 79 days of exposure, ozone reduced and elevated CO₂ increased net assimilation rate. However, the effect was dependent on daily accumulated exposure. No statistically significant differences in total plant mass accumulation were observed, although ozone-treated plants tended to be smaller. Changes in atmospheric gas concentrations induced changes in allocation of resources: under elevated ozone, shoots showed high priority over roots and had significantly elevated N concentrations. As a result of different shoot N concentration and net carbon assimilation rates, photosynthetic N use efficiency was significantly increased under elevated CO₂ and decreased under ozone. The differences in photosynthesis were mirrored in the growth of the fungus in symbiosis with the pine seedlings. However, exposure to CO₂ and ozone both reduced the symbiosis-mediated N uptake. The results suggest an increased carbon cost of symbiosis-mediated N uptake under elevated CO₂, while under ozone, plant N acquisition is preferentially shifted towards increased root uptake.     

Effects of intermittent exposure to high atmospheric CO2 on vegetative growth in soybean

Short-term exposure to high CO₂ increases rates of photosynthesis and growth in soybeans, but with prolonged high CO₂ exposure, these high rates are sometimes not maintained. Growth of soybean (Glycine max (L.) Merrill cv. Fiskeby V) seedlings kept for 25 days at atmospheres of 350 or 1000 μ/l CO₂ was compared with growth of plants given 2, 4 or 6 day alternating exposure to high and low CO₂ levels (13 days of total exposure to each level). Final dry weight of plants increased with number of days in high CO₂ but leaf areas were not greatly affected. Thus dry weight gains per unit leaf area (net assimilation rates) were higher in high CO₂ than in low CO₂ throughout the entire period of the experiment and the pattern of exposure to high CO₂ did not affect the rate of dry weight gain in high CO₂.     

Effects of manganese toxicity on leaf CO2 assimilation of contrasting common bean genotypes

Parameters related to leaf photosynthesis were evaluated in three genotypes of common bean ( Phaseolus vulgaris L.) with contrasting tolerance to Mn toxicity. Two short-term studies in solution culture were used to assess the effect of excess Mn on CO₂ assimilation in mature and immature leaves. Mn toxicity decreased total chlorophyll content only in immature leaves, with a consequent reduction of leaf CO₂ assimilation. Mature leaves that showed brown speckles characteristic of Mn toxicity, did not suffer any detriment in their capacity to assimilate CO₂, at least in a 4-day experiment. Stomatal conductance and transpiration were not affected by the presence of high levels of Mn in leaf tissue. Lower stomatal conductance and transpiration rates were observed only in leaves with advanced chlorosis. Differences among genotypes were detected as increased chlorosis in the more sensitive genotype ZPV-292, followed by A-283 and less chlorosis in the tolerant genotype CALIMA. Since CO₂ assimilation expressed per unit of chlorophyll was not different between high-Mn plants and control plants, we conclude that the negative effect of Mn toxicity on CO₂ assimilation can be explained by a reduction in leaf chlorophyll content.     

Physiological changes of Fagus sylvatica seedlings infected with Phytophthora citricola and the contribution of its elicitin "citricolin" to pathogenesis

Beech seedlings were infected with the root rot pathogen Phytophthora citricola to study its impact on leaf physiology and water status. Net photosynthesis rate decreased two days after inoculation in infected seedlings. In contrast, electron quantum yield of photosystem II, leaf water potential, and total water consumption were only slightly impaired until 6 dpi. At the same time, wilt symptoms occurred on leaves. These results indicate the involvement of a mobile signal triggering the early changes in leaf physiology by root infection. As the elicitin gene of P. citricola was induced during root infection, we purified and characterised the elicitin protein and tested its ability to change leaf physiological parameters of beech and tobacco plants. P. citricola produced a single acidic elicitin (citricolin), which caused necrosis and decreased gas exchange of tobacco leaves. Furthermore, it induced an oxidative burst in tobacco cell suspension culture. However, none of these effects were observed in beech.     

Elevated atmospheric CO2 influences the interaction between the parasitic angiosperm Orobanche minor and its host Trifolium repens

The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO₂ concentrations (350 and 550 μmol mol⁻¹). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root:shoot ratios) and within tissues:infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO₂. Elevated CO₂ stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO₂ on growth, with infected plants showing a greater response, such that elevated CO₂ partly alleviated the effects of the parasite on host growth. Elevated CO₂ did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO₂ but was unaffected by O. minor . There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO₂ in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO₂ on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO₂.     

A relationship between carbon dioxide, photosynthetic efficiency and shade tolerance

Net photosynthesis and transpiration of seedlings from shade tolerant, moderately tolerant and intolerant tree species were measured in ambient carbon dioxide (CO₂) concentrations ranging from 312 to 734 ppm. The species used, Fagus grandifolia Ehrh. (tolerant), Quercus alba L., Q. rubra L., Liriodendron tulipifera L. (moderately tolerant), Liquidambar styraciflua L. and Pinus taeda L. (intolerant), are found co-occurring in the mixed pine-hardwood forests of the Piedmont region of the southeastern United States. When seedlings were grown in shaded conditions, photosynthetic CO₂ efficiency was significantly different in all species with the highest efficiency in the most shade tolerant species, Fagus grandifolia , and progressively lower efficiencies in moderately tolerant and intolerant species. Photosynthetic CO₂ efficiency was defined as the rate of increase in net photosynthesis with increase in ambient CO₂ concentration. When plants which had grown in a high light environment were tested, the moderately tolerant and intolerant deciduous species had the highest photosynthetic CO₂ efficiencies but this capacity was reduced when these species grew in low light. The lowest CO₂ efficiency and apparent quantum yield occurred in Pinus taeda in all cases. Water use efficiency was higher for all species in enriched CO₂ environments but transpiration rate and leaf conductance were not affected by CO₂ concentration. High photosynthetic CO₂ efficiency may be advantageous for maintaining a positive carbon balance in the low light environment under a forest canopy.     

The effect of nitrogen source on photosynthesis of carob at high CO2 concentrations

Carob seedlings ( Ceratonia siliqua L. cv. Mulata), fed with nitrate or ammonium, were grown in growth chambers containing two levels of CO₂ (360 or 800 μl l⁻¹), three root temperatures (15, 20 or 25°C), and the same shoot temperature (20/24°C, night/day temperature). The response of the plants to CO₂ enrichment was affected by environmental factors such as the type of inorganic nitrogen in the medium and root temperature. Increasing root temperature enhanced photosynthesis rate more in the presence of nitrate than in the presence of ammonium. Differences in photosynthetic products were also observed between nitrate- and ammonium-fed carob seedlings. Nitrate-grown plants showed an enhanced content of sucrose, while ammonium led to enhanced storage of starch. Increase in root temperature caused an increase in dry mass of the plants of similar proportions in both nitrogen sources. The enhancement of the rates of photosynthesis by CO₂ enrichment was proportionally much larger than the resulting increases in dry mass production when nitrate was the nitrogen source. Ammonium was the preferred nitrogen source for carob at both ambient and high CO₂ concentrations. The level of photosynthesis of a plant is limited not only by atmospheric CO₂ concentration but also by the nutritional and environmental conditions of the root.     

Ecophysiological responses to simulated canopy gaps of two tree species of contrasting shade tolerance in elevated CO2

1. One-year-old seedlings of shade tolerant Acer rubrum and intolerant Betula papyrifera were grown in ambient and twice ambient (elevated) CO₂, and in full sun and 80% shade for 90 days. The shaded seedlings received 30-min sun patches twice during the course of the day. Gas exchange and tissue–water relations were measured at midday in the sun plants and following 20 min of exposure to full sun in the shade plants to determine the effect of elevated CO₂ on constraints to sun-patch utilization in these species.
2. Elevated CO₂ had the largest stimulation of photosynthesis in B. papyrifera sun plants and A. rubrum shade plants.
3. Higher photosynthesis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology. Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade.
4. Betula papyrifera exhibited CO₂ responses that would facilitate tolerance to leaf water deficits in large sun patches, including osmotic adjustment and higher transpiration and stomatal conductance at a given leaf-water potential, whereas A. rubrum exhibited large increases in photosynthetic nitrogen-use efficiency.
5. Results suggest that species of contrasting successional ranks respond differently to elevated CO₂, in ways that are consistent with the habitats in which they typically occur.     

Relationships between nitrogen uptake and carbon assimilation in whole plants of tall fescue

Abstract. The present study investigates the relationships between nitrogen uptake, transpiration, and carbon assimilation. Plants growing on nutrient solution were enclosed for 10–16 d in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO₂ concentration were controlled. One of these factors was modified every 4 to 5 d. Shoot photosynthesis and root and shoot respiration were recorded every half-hour. Nitrogen uptake from the root medium and plant transpiration were measured daily. In most cases, an increase in photon flux density led to increases in transpiration, net daily carbon assimilation, and nitrogen uptake. By modifying transpiration rate without changing photosynthesis (varying vapour saturation deficit), or by modifying transpiration and carbon assimilation in opposite ways (varying CO₂ air concentration), it was shown that nitrogen uptake does not follow transpiration, but is linked to the carbon uptake of the plant. When light was increased from low to intermediate levels, the N uptake/C assimilation ratio remained constant. At higher photon flux density, this ratio declined markedly. It is proposed that in the first case, growth is limited by carbohydrate availability, thus any increase in carbon assimilation leads to a proportional increase in nitrogen uptake, in contrast to the second situation where carbohydrates may accumulate in the plant without further nitrogen requirement.     

Growth and physiological responses of canola (Brassica napus) to UV-B and CO2 under controlled environment conditions

Few studies have investigated the interaction of ultraviolet (UV)-B radiation and CO₂ concentration on plants. We studied the combined effects of UV-B radiation and CO₂ concentration on canola ( Brassica napus cv. 46A65) under four growth conditions – ambient CO₂ with UV-B (control), elevated CO₂ with UV-B, ambient CO₂ without UV-B, and elevated CO₂ without UV-B – to determine whether the adverse effects of UV-B are mitigated by elevated CO₂. Elevated CO₂ significantly increased plant height and seed yield, whereas UV-B decreased them. Elevated CO₂ ameliorated the adverse effects of UV-B in plant height. UV-B did not affect the physical characteristics of leaf but CO₂ did. Certain flower and fruit characteristics were affected negatively by UV-B and positively by CO₂. UV-B did not affect net photosynthesis, transpiration and stomatal conductance but decreased water use efficiency (WUE). Elevated CO₂ significantly increased net photosynthesis and WUE. Neither UV-B nor CO₂ affected chlorophyll (Chl) fluorescence. UV-B significantly decreased Chl b and increased the ratio of Chl a / b . Elevated CO₂ decreased only the ratio of Chl a / b . UV-B significantly increased UV-absorbing compounds while CO₂ had no effect on them. Both UV-B and CO₂ significantly increased epicuticular wax content. Many significant relationships were found between morphological, physiological, and chemical parameters. This study showed that elevated CO₂ can partially ameliorate some of the adverse effects of UV-B radiation in B . napus .     

Mycorrhiza formation and elevated CO2 both increase the capacity for sucrose synthesis in source leaves of spruce and aspen

The effects of mycorrhiza formation in combination with elevated CO₂ concentrations on carbon metabolism of Norway spruce ( Picea abies ) seedlings and aspen ( Populus tremula × Populus tremuloides ) plantlets were analysed. Plants were inoculated for 6 wk with the ectomycorrhizal fungi Amanita muscaria and Paxillus involutus (aspen only) in an axenic Petri-dish culture at 350 and 700 μl l⁻¹ CO₂ partial pressure. After mycorrhiza formation, a stimulation of net assimilation rate was accompanied by decreased activities of sucrose synthase, an increased activation state of sucrose-phosphate synthase, decreased fructose-2,6-bisphosphate and starch, and slightly elevated glucose-6-phosphate contents in source leaves of both host species, independent of CO₂ concentration. Exposure to elevated CO₂ generally resulted in higher net assimilation rates, increased starch as well as decreased fructose-2,6-bisphosphate (aspen only) content in source leaves of both mycorrhizal and nonmycorrhizal plants. Our data indicate only slightly improved carbon utilization by mycorrhizal plants at elevated CO₂. They demonstrate however, that both factors which modulate the sink-source properties of plants increase the capacity for sucrose synthesis in source leaves mainly by allosteric enzyme regulation.     

Physiological effects of sulphur dioxide. 1. The effect of SO2 on photosynthesis and stomatal regulation of Vicia faba L.

Abstract. The effect of short-term SO₂ fumigation on photosynthesis and transpiration of Vicia faba L. was measured at different irradiances and SO₂ concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO₂ and the magnitude of the reduction was linearly related to the rate of SO₂ uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.
The effect of SO₂ on photosynthesis was measured at different CO₂ concentrations to analyse the contribution of stomatal and non-stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO₂ diffusion increased as a result of SO₂ exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO₂ fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO₂ concentration.
Analysis of gas-exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO₂ exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO₂ than for O₂.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

How does the C4 grass Eragrostis pilosa respond to elevated carbon dioxide and infection with the parasitic angiosperm Striga hermonthica?

Eragrostis pilosa (Linn.) P Beauv., a C₄ grass native to east Africa, was grown at both ambient (350 μmol mol⁻¹ and elevated (700 μmol mol⁻¹) CO₂ in either the presence or absence of the obligate, root hemi-parasite Striga hermonthica (Del.) Benth. Biomass of infected grasses was only 50% that of uninfected grasses at both CO₂ concentrations, with stems and reproductive tissues of infected plants being most severely affected. By contrast, CO₂ concentration had no effect on growth of E. pilosa , although rates of photosynthesis were enhanced by 30–40% at elevated CO₂. Infection with S. hermonthica did not affect either rates of photosynthesis or leaf areas of E. pilosa , but did bring about an increase in root:shoot ratio, leaf nitrogen and phosphorus concentration and a decline in leaf starch concentration at both ambient and elevated CO₂. Striga hermonthica had higher rates of photosynthesis and shoot concentrations of soluble sugars at elevated CO₂, but there was no difference in biomass relative to ambient grown plants. Both infection and growth at elevated CO₂ resulted in an increase in the Δ¹³C value of leaf tissue of E. pilosa , with the CO₂ effect being greater. The proportion of host-derived carbon in parasite tissue, as determined from δ¹³C values, was 27% and 39% in ambient and elevated CO₂ grown plants, respectively. In conclusion, infection with S. hermonthica limited growth of E. pilosa , and this limitation was not removed or alleviated by growing the association at elevated CO₂.     

Inhibition of photosynthesis and transpiration in relation to mercury-induced root damage in spruce seedlings

Spruce seedlings [ Picea abies (L.) Karst.] were exposed in nutrient solutions to a range of concentrations of HgCl₂ and CH₃HgCl for 7 weeks. The mineral, chlorophyll and water contents of the needles, and dry weights of root and needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plants were determined using a Li-cor portable photosynthesis-measuring system. CO₂ uptake decreased as the supply of both forms of Hg increased. Rates of transpiration were significantly reduced only after exposure to CH₃HgCl. Similar concentrations of Hg were found in needles independent of the form of Hg supplied. Decreased rates of CO₂ uptake at 100 n M HgCl₂ and 1 n M CH₃HgCl could be explained by lower levels of chlorophyll, and by lower levels of chlorophyll and closed stomata at all other CH₃HgCl concentrations. Only at 1000 n M HgCl₂ were other photosynthetic parameters affected.
Decreased rates of transpiration and the lower chlorophyll levels in the needles did not appear to be due to the direct action of Hg, but rather to root damage that leads to a decrease in water supply and nutrient levels in the needles.     

Canopy photosynthesis of crops and native plant communities exposed to long-term elevated CO2

Abstract. There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO₂: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO₂ increased canopy photosynthesis in all cases. The relative effect of CO₂ was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10°C and the greatest in rice grown at 43°C. In soybean, effects of CO₂ were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO₂ treatment to date, monospecific stands of a C₃ sedge, Scirpus olneyi (Grey), and a C₄ grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO₂ concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO₂ exchange per unit green biomass (NCE_b) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO₂ increased net ecosystem carbon assimilation by 88% in the Scirpus olneyi community and 40% in the Spartina patens community.     

The response of nodulated alfalfa to water supply, temperature and elevated CO2: photosynthetic downregulation

Plants grown in an environment of elevated CO₂ and temperature often show reduced CO₂ assimilation capacity, providing evidence of photosynthetic downregulation. The aim of this study was to analyse the downregulation of photosynthesis in elevated CO₂ (700 µmol mol⁻¹) in nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4°C) and water availability regimes in temperature gradient tunnels. When the measurements were taken in growth conditions, a combination of elevated CO₂ and temperature enhanced the photosynthetic rate; however, when they were carried out at the same CO₂ concentration (350 and 700 µmol mol⁻¹), elevated CO₂ induced photosynthetic downregulation, regardless of temperature and drought. Intercellular CO₂ concentration measurements revealed that photosynthetic acclimation could not be accounted for by stomatal limitations. Downregulation of plants grown in elevated CO₂ was a consequence of decreased carboxylation efficiency as a result of reduced rubisco activity and protein content; in plants grown at ambient temperature, downregulation was also induced by decreased quantum efficiency. The decrease in rubisco activity was associated with carbohydrate accumulation and depleted nitrogen availability. The root nodules were not sufficiently effective to balance the source–sink relation in elevated CO₂ treatments and to provide the required nitrogen to counteract photosynthetic acclimation.     

The effect of an elevated atmospheric CO2 concentration on growth, photosynthesis and respiration of Plantago major

The effect of an elevated atmospheric CO₂ concentration on growth, photosynthesis and root respiration of Plantago major L. ssp. major L. was investigated. Plants were grown in a nutrient solution in growth chambers at 350 and 700 μl I⁻¹ CO₂ during 7 weeks. The total dry weight of the Co₂-enriched plants at the end of this period was 50% higher than that of control plants. However, the relative growth rate (RGR) was stimulated only during the first half of the growing period. The transient nature of the stimulation of the RGR was not likely to be due to end-product inhibition of photosynthesis. It is suggested that in P. major , a rosette plant, self-shading causes a decline in photosynthesis and results in an increase in the shoot: root ratio and a decrease in RGR. CO₂-enriched plants grow faster and cosequently suffer more from self-shading. Corrected for this ontogenetic drift, high CO₂ concentrations stimulated the RGR of P. major throughout the entire experiment.     

Effect of root zone carbon dioxide enrichment on ethylene inhibition of carbon assimilation in potato plants

Potato plants ( Solanum tuberosum L. var. Russet Burbank) treated with 1 μl ethylene 1⁻¹ of air showed an inhibition of CO₂ assimilation by 18%. The inhibition occurred after 3 h of exposure to ethylene and was not mediated through closure of the stomata. The enrichment of the root zone with CO₂ almost completely abolished the ethylene inhibition of CO₂ assimilation which was apparently due to an increase in the intercellular concentration of CO₂ in leaves following enrichment. The effect of application of CO₂ to the root zone on ethylene inhibition of CO₂ assimilation seemed to last for a few days. Potato plants treated with aminoethoxyvinlglycine (AVG) showed an increase in fresh and dry weight as compared to non-treated plants. Our results indicate that both CO₂ and AVG alter the effect of ethylene and promote growth in plants by inhibiting ethylene action and biosynthesis, respectively.