Effect of chromium species on phytochemical and physiological parameters in Datura innoxia

In soil, chromium can be found in two main valence states: hexavalent Cr(VI) and trivalent Cr(III). In this study, we investigated the impact of Cr on photosynthetic gas exchange, photosystem II (PSII) activity, Cr translocation and accumulation, proline content and alkaloids production, i.e. scopolamine and hyoscyamine, in Datura innoxia. Cr uptake was influenced by its oxidation state and its concentration in growth medium. The plant roots were determined as being the main organ of Cr accumulation. Cr(VI) was more toxic than Cr(III) as indicated by reduction in plant biomass and net photosynthesis. The stomatal conductance showed a similar trend to that of photosynthetic capacity. Cr(III) and Cr(VI) had a different impact on substomatal CO(2) concentration then Cr toxicity was related to its oxidation states. In plants stressed with a Cr(VI) excess, a down regulation of PSII activity was observed with an impairment of photochemical activity. Indeed, the maximum quantum yield of PSII (F(v)/F(m)), the quantum yield of PSII (PhiPSII) and the efficiency of excitation capture by open centers (F'(v)/F'(m)) decreased. Cr(III) had little effects on PSII primary photochemistry, whatever its form induces an increase of scopolamine content without changes in hyoscyamine content in leaves of D. innoxia. These results provide that chromium contamination can change the secondary metabolites composition of leaves, thereby, impacting the quality, safety and efficacy of natural plant products synthesized by D. innoxia plants.     

Comparative study of responses in four Datura species to a zinc stress

The effects of zinc toxicity on the growth and the photosynthetic activities of four Datura species (Datura metel, Datura innoxia, Datura sanguinea, Datura tatula) were studied using various ZnSO4 concentrations (0, 1, 2.5 and 5 mM) added in the Coic Lessaint solution. Growth, photosynthesis, chlorophyll fluorescence and chlorophyll concentration were measured after 20 days of zinc stress. These parameters were severely reduced by this heavy metal. The zinc excess involves the stomate closing, the increase of CO2 concentration in the leaves, the inhibition of certain enzyme of the Calvin cycle, a degradation of photosystem and the chlorophyll decomposition. These phenomena allow the decrease of the net photosynthesis to be partially explained. These key parameters to assess photosynthetic performance allow the plants to be classified according to their resistance to zinc. Compared with the three other species, D. innoxia showed a very strong capacity to protect itself against toxic zinc concentrations; a large amount of ZnSO4 (5 mM) was required to inhibit 43% of the photosynthesis.     

Multiple effects of chromate on the photosynthetic apparatus of Spirodela polyrhiza as probed by OJIP chlorophyll a fluorescence measurements

Chromate (Cr) decreases the growth of Spirodela polyrhiza. The fronds lost their pigments. The O2 evolution was also decreased. The Cr effect was found to be dose dependent. The toxic effects of Cr have further been studied on the photosynthetic activity of Spirodela polyrhiza by means of the chlorophyll a (Chl a) fluorescence transient O-J-I-P. The Chl a fluorescence transients were recorded in vivo with high time resolution and analyzed according to the JIP-test which can quantify the photosystem II behavior. Cr treated plants show a decrease in yield for primary photochemistry, phi Po. The performance index of PSII, PIABS, which is the combination of the indexes of three independent parameters, (1) the total number of active reaction centers per absorption (RC/ABS), (2) yield of primary photochemistry (phi Po) and (3) efficiency with which a trapped exciton can move an electron into the electron transport chain (psi 0), decreased due to Cr treatment. Chromate sensitivity varies within plant populations. In summary Cr affects several targets of PSII. More specifically, the main targets of Cr, according to the JIP-test, can be listed as a decrease in the number of active reaction centers and damage to the oxygen-evolving complex.     

The effects of coal dust on photosynthetic performance of the mangrove, Avicennia marina in Richards Bay, South Africa

Richards Bay, on the northern KwaZulu-Natal coast, is the largest coal exporting port in South Africa. The coal is stored at the Richards Bay Coal Terminal (RBCT) prior to export. Dust from coal operations is a major problem in the Richards Bay area. In this study, we tested the hypothesis that coal dust adversely affects photosynthetic performance of Avicennia marina (Forssk.) Vierh., the dominant mangrove species in the harbour. Photosynthetic performance was determined on 10 trees by measuring carbon dioxide uptake and chlorophyll fluorescence parameters at two elevation sites and on upper and lower leaf surfaces that were covered or uncovered with coal dust. Measurements were made on five clear, sunny days at saturating light (>1,000 micromol m(-2)s(-1)) and high temperature (28-30 degrees C). Coal dust significantly reduced carbon dioxide exchange of upper and lower leaf surfaces by 17-39%, the reduction being generally greater on the lower leaf surface that is covered by a dense mat of trichomes and salt glands. The reduction in carbon dioxide exchange by coal dust was higher at the high elevation site that supported isolated dwarfed trees. The chlorophyll fluorescence data indicated that leaves coated with dust exhibited significantly lower photosystem II (PS II) quantum yield, lower electron transport rate (ETR) through PSII and reduced quantum efficiency of PSII (FvFm). The chlorophyll fluorescence data supported the gas exchange measurements and are consistent with reduced photosynthetic performance of leaves coated with coal dust.     

Growth, photosynthetic and respiratory responses to sub-lethal copper concentrations in Scenedesmus incrassatulus (Chlorophyceae)

In the present paper we investigated the effects of sub-lethal concentrations of Cu²⁺ in the growth and metabolism of Scenedesmus incrassatulus. We found that the effect of Cu²⁺ on growth, photosynthetic pigments (chlorophylls and carotenoids) and metabolism do not follow the same pattern. Photosynthesis was more sensitive than respiration. The analysis of chlorophyll a fluorescence transient shows that the effect of sub-lethal Cu²⁺ concentration in vivo, causes a reduction of the active PSII reaction centers and the primary charge separation, decreasing the quantum yield of PSII, the electron transport rate and the photosynthetic O₂ evolution. The order of sensitivity found was: Growth > photosynthetic pigments content = photosynthetic O₂ evolution > photosynthetic electron transport > respiration. The uncoupled relationship between growth and metabolism is discussed.     

Effects of cadmium on the activities of photosystems of Chlorella pyrenoidosa and the protective role of cyclic electron flow

Cadmium (Cd) shows high toxicity to aquatic microalgae. Many studies showed that Cd inhibited activities of photosystem II (PSII) but the effects of heavy metals on photosystem I (PSI) and cyclic electron flow (CEF) were still controversial and unclear. The effects of CdCl₂ on the activities of PSI, PSII and CEF in Chlorella pyrenoidosa was measured simultaneously in the present study. In presence of 200 μM of Cd, ultrastructure of some cells was strongly modified. Cd exposure led to decrease of the activities of photosynthetic oxygen evolution and respiration. PSII was more sensitive to Cd treatment than PSI. Cd treatment showed significant inhibition on the photochemical quantum yield and electron transport rate of PSII. Cd increased the quantum yield of non-light-induced non-photochemical fluorescence quenching, indicating the damage of PSII. The activity of PSI showed tolerance to Cd treatment with concentration less than 100 μM in the experiment. Linear electron flow (LEF) made significant contribution to the photochemical quantum yield of PSI of the untreated cells, but decreased with increasing Cd concentration. The contribution of CEF to the yield of PSI increased with increasing Cd concentration. The activation of CEF after exposure to Cd played an essential role for the protection of PSI.     

Effect of the herbicide flumioxazin on photosynthetic performance of grapevine (Vitis vinifera L.)

Among the herbicides used in vineyards, the pre-emergence soil-applied flumioxazin (fmx) is a recently used molecule that inhibits chlorophyll biosynthesis in weed species. The aim of this work is to further characterize the effects of fmx on the non-target grapevine (Vitis vinifera L. cv. Chardonnay) using cutting as a model. Several photosynthesis parameters were estimated during 25 days after treatment with various fmx concentrations (from 0.5mM to 50mM). Measuring chlorophyll fluorescence it appeared that fmx or a by-product penetrated the plant throughout roots and spread throughout vessels. Besides the initial target, protox, fmx affected other functions related to photosynthesis. Fmx induced a simultaneous drop of both P(n), g(s) and T. Fmx caused stomatal closure, which partially explains the decrease of the net photosynthesis. The decline in F(v)/F(m) indicates that the photochemistry of PSII and its ability to reduce the primary acceptor Q(A) are also affected by fmx in grapevine. Fmx leads to a decrease in the coefficients of both photochemical and non-photochemical quenching. Simultaneous stomatal closure and decrease in the quantum yield of CO(2) assimilation indicate a change in energy metabolism following fmx stress. After ten days of fmx treatment, analyses of the response of net carbon assimilation in leaves to different intercellular CO(2) concentrations have shown a decrease of the maximum carboxylation velocity of RuBP. Stomatal closure, PSII photochemistry, change in energy metabolism and RuBP activity were affected by fmx treatment.     

Validation of photosynthetic-fluorescence parameters as biomarkers for isoproturon toxic effect on alga Scenedesmus obliquus

Photosynthetic-fluorescence parameters were investigated to be used as valid biomarkers of toxicity when alga Scenedesmus obliquus was exposed to isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] effect. Chlorophyll fluorescence induction of algal cells treated with isoproturon showed inactivation of photosystem II (PSII) reaction centers and strong inhibition of PSII electron transport. A linear correlation was found (R2>or=0.861) between the change of cells density affected by isoproturon and the change of effective PSII quantum yield (PhiM'), photochemical quenching (qP) and relative photochemical quenching (qP(rel)) values. The cells density was also linearly dependent (R2=0.838) on the relative unquenched fluorescence parameter (UQF(rel)). Non-linear correlation was found (R2=0.937) only between cells density and the energy transfer efficiency from absorbed light to PSII reaction center (ABS/RC). The order of sensitivity determined by the EC-50% was: UQF(rel)>PhiM'>qP>qP(rel)>ABS/RC. Correlations between cells density and those photosynthetic-fluorescence parameters provide supporting evidence to use them as biomarkers of toxicity for environmental pollutants.     

Interaction of bioaccumulation of heavy metal chromium with water relation, mineral nutrition and photosynthesis in developed leaves of Lolium perenne L

Contamination by chromium (Cr) is widespread in agricultural soils and industrial sites. This heavy metal represents a risk to human health. In order to gain fundamental insights into the nature of the adaptation to Cr excess, the characterisation of physiological indices, including responses of photosynthetic gas exchange and chlorophyll a fluorescence along with changes in mineral nutrient contents and water status were studied in ray grass (Lolium perenne L.). Increased concentrations of Cr(VI) (0-500 microM Cr) in the Co?c and Lessaint nutrient solution were applied. The growth of Lolium perenne is decreased by chromium and the leaves have lost their pigments. Chromium accumulation was greater in roots than in leaves and reached 2450 and 210 microg g(-1) DW, respectively with 500 microM Cr(VI) in nutrient medium. The physiological parameters were severely reduced by this heavy metal. Cr induced toxicity arising from 100 microM Cr(VI) and resulted in a modification of mineral content in roots and leaves, especially for Ca, Mg and Fe. The chromium stress decreased CO2 assimilation rates mainly due to stomatal closure, which reduced water loss by transpiration without decreasing the cellular available CO2. The fluorescence parameters associated with photosystem II (PSII) activity and the photochemical activity are modified by chromium. Non-radiative energy dissipation mechanisms were triggered during stress since non-photochemical quenching was increased and efficiency of excitation capture by open centers was reduced.     

Bioaccumulation and physiological effects of mercury in Sesbania drummondii

The accumulation of mercury and its effect on growth, photosynthesis and antioxidative responses were studied in Sesbania drummondii seedlings. Mercury concentration in shoots as well as in the roots increased with increasing Hg concentrations in the growth solution. The accumulation of Hg was more in roots than shoots. At 100 mg l-1 Hg concentration, shoots accumulated 998 mg Hg kg -1 dry weight (dw) while roots accumulated 41,403 mg Hg kg-1 dw. Seedlings growth was not significantly affected at lower concentrations of Hg. A concentration of 100 mg l-1 Hg inhibited growth by 36.8%, with respect to control. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was not affected up to 50 mg l-1 Hg concentration, however, concentrations higher than 50 mg l-1 affected photosynthetic integrity. Sesbania responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants [glutathione (GSH) and non-protein thiols (NPSH)] and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). Glutathione content and GSH/GSSG ratio increased up to a concentration of 50 mg l-1 while slight down at 100 mg l-1 Hg. The content of NPSH significantly increased with increasing Hg concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX and GR followed the same trends as antioxidants first increased up to a concentration of 50 mg l-1 Hg and then slight decreased. The results of present study suggest that Sesbania plants were able to accumulate and tolerate Hg induced stress using an effective antioxidative defense mechanisms.     

Effects of cadmium on the photosynthetic activity in mature and young leaves of soybean plants

Cadmium (Cd) is a widely spread pollutant and can be easily taken up by crop from soil, resulting in a serious health issue for humans. The objective of this study was to comparatively investigate the photosynthetic activity, chlorophyll a fluorescence, chlorophyll contents, and spectral reflectance in mature and young leaves of soybean plants after being treated with different concentrations of Cd for 10 days. The photosynthetic rate, chlorophyll contents, actual photochemical efficiency of PSII, and photochemical quenching in the young leaves decreased more significantly with increasing concentrations of Cd in the nutrient solution, compared with those in the mature leaves, though the young leaves had less Cd concentrations. Thus, there was more excessive excited energy produced in the young leaves than that in the mature leaves. In the young leaves, due to more excessive excited energy, more reactive oxygen species may be generated, which further damaged the photosynthetic apparatus. It was supported by the fact that the decrease of reflectance in near-infrared wavelengths of the young leaves was more noticeable than that of the mature leaves. In addition, the chlorophyll a fluorescence transients of the young leaves was significantly different from that in the mature leaves, indicating that the electron transport of young leaves were inhibited much more severely than that of the mature leaves. These observations imply that the responses of photosynthetic activity of soybean leaves to Cd stress depend on their growth stage, and the Cd-induced inhibition of photosynthetic activity might be attributed to the decrease in chlorophyll contents and the decrease in mesophyll CO₂ assimilation ability cause by the Cd, which further decreased the consumption of ATP and NADPH, leading to accumulation of NADPH on the acceptor sides of the PSI, and then feedback inhibited electron transport in chloroplasts.     

Intact anthracene inhibits photosynthesis in algal cells: a fluorescence induction study on Chlamydomonas reinhardtii cw92 strain

Short-term (24h) experiments were performed to examine the effect of anthracene (ANT) on Chlamydomonas reinhardtii cw92 grown in a batch culture system aerated with 2.5% CO(2). At concentrations ranging from 0.7 to 5.6 microM, ANT inhibited the growth of population in a concentration-dependent manner and EC(50) calculated amounted to 1.6 microM. At concentrations from 0.7 to 4.2 microM ANT stimulated respiration and inhibited the intensity of photosynthesis but did not affect chlorophyll content in the cells. ANT influenced chlorophyll a fluorescence parameters, measured by OJIP test (O, J, I and P are the different steps of fluorescence induction curve). ANT diminished the performance index (PI), the yield of primary photochemistry (phi(Po)), the yield of electron transport (phi(Epsilonomicron), the efficiency of moving the electron beyond Qa(-) (Psi(0)) and the fraction of active oxygen evolving complexes (OEC). The fraction of active PS II reaction centres in the treated samples dramatically dropped. The most pronounced changes in ANT-treated cells were observed in the stimulation of energy dissipation parameter (DI(0)/RC). The only OJIP parameter that was not influenced by ANT was energy absorption by photosynthetic antennae (ABS). The results lead to a conclusion that the inhibition of photosynthesis may be a consequence of unspecific ANT-membrane interaction, resulting from hydrophobic character of this hydrocarbon.     

Variation in oxidative stress and photochemical activity in Arabidopsis thaliana leaves subjected to cadmium and excess copper in the presence or absence of jasmonate and ascorbate

We have presented changes in the photosynthetic apparatus activity of Arabidopsis thaliana plants occurring within 15-144 h of 100 microM Cu or Cd action with regard to jasmonate (JA) as well as expression of the oxidative stress and non-enzymic defense mechanisms. The inhibitory effect of both heavy metals related to developing dissipative processes and lipid peroxide formation was expressed in dark-adapted state after the longest time as a decrease in potential quantum yield of PSII. In dark- and light-adapted state the heavy metals affected the enzymic phase of photosynthesis already from the 15th hour, which was related to the lipid peroxide formation. Photochemical quenching decrease was induced after 48th hour and did not show a close correlation with the JA pathway. Blockade of endogenously formed JA by propyl gallate decreased the effect of Cu and Cd on both the whole photosynthetic apparatus starting from the 48th hour and on the primary photochemistry of PSII after 144 h. In the case of Cu the effect was related to a lipid peroxidation decrease and to an increase in glutathione and phytochelatin (PC) levels, but in the case of Cd to lipid peroxidation, O.2- and especially to PCs increase. The obtained results indicated that JA after the longest time might enhance the sensitivity of A. thaliana to Cu and Cd stress. Asc enhanced toxic action of Cu and Cd after 15 h, but after a longer time it diminished the influence of Cd (but not Cu) on photosynthetic activity.     

Evaluation of different algal species sensitivity to mercury and metolachlor by PAM-fluorometry.

In this study, the pulse-amplitude-modulation (PAM)-fluorometric method was used to evaluate the difference in the sensitivity to mercury (Hg) and metolachlor of six algal species: Ankistrodesmus falcatus, Selenastrum capricornutum, Chlorella vulgaris, Nannoplankton (PLS), Microcystis aeruginosa and Pediastrum biwae. We found that the fluorescence parameters (phiM, the maximal photosystem II (PSII) quantum yield, phi'M, the operational PSII quantum yield at steady state of electron transport, Q(P), the photochemical quenching value, and Q(N), the non-photochemical quenching value) were appropriate indicators for inhibitory effects of mercury but only phi'M and Q(N) were useful for metolachlor. The examined algal species showed very different levels of sensitivity to the effect of Hg and of metolachlor. The most sensitive species to Hg and metolachlor were respectively M. aeruginosa and A. falcatus, while the least sensitive were C. vulgaris and P. biwae. We interpreted these differences by the action mode of pollutants and by the different metabolism properties and morphological characteristics between algal species. These results related to fluorescence parameters may offer useful tool to be used in bioassay for different pollutants. Heterogeneous algal sensitivity to the same pollutant suggests the need to use a battery of species to evaluate the effects of mixtures of pollutants in aquatic systems.     

Brassinosteroid alleviates phenanthrene and pyrene phytotoxicity by increasing detoxification activity and photosynthesis in tomato

The present study was carried out to investigate the effects of exogenously applied 24-epibrassinolide (BR) on growth, gas exchange, chlorophyll fluorescence characteristics, lipid peroxidation and antioxidant systems of tomato seedlings grown under different levels (0, 10, 30, 100 and 300 μM) of phenanthrene (PHE) and pyrene (PYR) in hydroponics. A concentration-dependent decrease in growth, photosynthetic pigment contents, net photosynthetic rate (Pn), stomatal conductance (Gs), maximal quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (Φ_PSII), photochemical quenching coefficient (qP) has been observed following PHE and PYR exposure. By contrast, non-photochemical quenching coefficient (NPQ) was increased. PHE was found to induce higher stress than PYR. However, foliar or root application of BR (50 nM and 5 nM, respectively) alleviated all those depressions with a sharp improvement in the activity of photosynthetic machinery. The activities of guaicol peroxidase (GPOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as content of malondialdehyde (MDA) were increased in a dose-dependent manner under PHE or PYR treatments. Compared with control the highest increments of GPOD, CAT, APX, GR and MDA by PHE/PYR alone treatments were observed following 300 μM concentration, which were 67%, 87%, 53%, 95% and 74% by PHE and 42%, 53%, 30%, 86% and 62% by PYR, respectively. In addition, both reduced glutathione (GSH) and oxidized glutathione (GSSG) were induced by PHE or PYR. Interestingly, BR application in either form further increased enzymatic and non enzymatic antioxidants in tomato roots treated with PHE or PYR. Our results suggest that BR has an anti-stress effect on tomato seedlings contaminated with PHE or PYR and this effect is mainly attributed by increased detoxification activity.     

Temperature influence on silver nanoparticles inhibitory effect on photosystem II photochemistry in two green algae, Chlorella vulgaris and Dunaliella tertiolecta

Purpose

In this study, the effect of silver nanoparticles (AgNPs) on the photosynthetic performance of two green algae, Chlorella vulgaris and Dunaliella tertiolecta, was investigated at 25°C and 31°C.

Methods

To induce AgNPs effect, algal cells were exposed for 24?h to concentrations varying from 0 to 10?mg/L. The polyphasic OJIP fluorescence transient was used to evaluate photosystem II (PSII).

Results

We show that growth media and temperature had different effects in AgNPs agglomerates formation and Zeta potential. When temperature conditions change, inhibitory effect of AgNPs also undergoes changes. Increase of temperature induced higher altering effects to PSII quantum yield, primary photosynthetic electron transport, and consequently higher decrease of total photosynthetic performance if compared to AgNPs effect alone. AgNPs has a negative effect on D. tertiolecta compared to C. vulgaris.

Conclusion

We conclude that temperature tends to enhance the toxic effects on aquatic alga and these alterations might have serious consequences on ecosystem equilibrium and aquatic plant communities.     

Chlorophyll a fluorescence, antioxidant enzymes and lipid peroxidation in tomato in response to ozone and benomyl.

Ozone is a widely distributed phytotoxic air pollutant and is known to reduce the yield of several important agricultural crops in Spain. However, benomyl has been found to lessen the adverse impact of ozone on plants. We studied the effects of ozone and benomyl on chlorophyll a fluorescence, antioxidant enzymes, and lipid peroxidation in tomato (Lycopersicon esculentum Mill. cv. Tiny Tim) grown in open-top chambers in the field. Our results indicate that benomyl prevented the peroxidation of membrane lipids and increased protection of PSII from ozone. There was also a significant reduction in the activity of the antioxidant enzyme superoxide dismutase in ozone-exposed plants that had not been treated with benomyl. Comparing plants treated with benomyl to untreated plants we found that, on exposure to ozone, a greater fraction of light absorption energy was cycled through the photosynthetic system in benomyl-treated plants, as shown by the higher PSII-mediated electron flow and the higher fraction of open PSII reaction centers. The values analyzed in the fluorescence parameters and lipid peroxidation were similar for plants without benomyl grown in a charcoal-filtered environment and benomyl-treated plants exposed to ozone.     

Effect of herbicide and soil amendment on growth and photosynthetic responses in olive crops

Diuron [3-(3,4-dichlorophenyl)- = 1,1-dimethylurea] and simazine (6-chloro-N(2), N(4)-diethyl-1,3,5-triazine-2,4-diamine) are soil-applied herbicides used in olive crops. The objective of this study is to investigate the combined effect of these herbicides and the amendment of soil with an organic waste (OW) from the olive oil production industry on the growth and photosynthetic apparatus of adult olive trees and to compare the results with those obtained by Redondo-Gómez et al. for two-year-old trees. For this purpose, growth rate, gas exchange and chlorophyll fluorescence parameters were measured in 38-year-old olive trees, after one and two months of soil herbicide treatment and/or OW amendment. Soil co-application of OW and herbicide increases the quantum efficiency of Photosystem II (PSII) and the assimilation of CO(2) in olive trees, which led to a higher relative growth rate of the branches and leaves in length. Herbicide treatment reduced the photosynthetic efficiency in olive trees after two months of soil application, while this reduction is evident from week one in younger trees.     

Physiological effects of mercury in the lichens Cladonia arbuscula subsp. mitis (Sandst.) Ruoss and Peltigera rufescens (Weiss) Humb

This study aimed at investigating the cellular distribution of Hg in the lichens Cladonia arbuscula subsp. mitis and Peltigera rufescens treated with Hg²⁺ and at testing if Hg treatment affects selected physiological parameters. In both species, increasing Hg accumulation under increasing Hg supply in the treatment solutions was found. P. rufescens showed a higher intracellular accumulation. Photosynthetic parameters were negatively affected in both species, as indicated by the decrease in photosynthetic pigments content, photosynthetic efficiency and chlorophyll integrity. Cell membranes of both species endured damage as indicated by the increase in the concentration of products of lipid peroxidation and decrease in ergosterol content. Nevertheless, differences between the two species were found, suggesting a differential sensitivity to Hg.     

Effects of elevated O3 and CO2 on chlorophyll fluorescence and gas exchange in Scots pine during the third growing season

Naturally regenerated, 30-year-old Scots pines (Pinus Sylvestris L.) were grown in open-top chambers and exposed in situ to doubled ambient O(3), doubled ambient CO(2) and a combination of elevated O(3) and CO(2) from 15 April to 15 September for three growing seasons (1994-1996). To examine the effects of O(3) and/or CO(2) on photosynthesis, chlorophyll a fluorescence and gas exchange were measured simultaneously. Doubled ambient O(3) significantly decreased the rates of photosynthesis at all levels of photon flux density. This was related mainly to a significant decrease in the photochemical efficiency of photosystem II (PS II) and the rate of whole electron transport, rather than to a decrease in stomatal conductance. When measurements were made at doubled ambient concentration of CO(2) (700 micromol mol(-1)), doubled ambient CO(2) treatment did not lead to a significant change in the intrinsic capacity of photosynthesis, as manifested by no changes in PS II, the rate of electron transport, the maximal rate of photosynthesis and the apparent quantum yield of CO(2) assimilation. However, elevated CO(2) increased the sensitivity of stomatal conductance to light and decreased maximal stomatal conductance. When O(3) and CO(2) were combined, the O(3)-induced decrease in photosynthesis rate was reduced significantly by a high concentration of CO(2). This may be partly related to the decrease in stomatal conductance induced by the high concentration of CO(2). The complete mechanism behind this interaction is, however, still unclear.