Influence of light fleck and low light on foliar injury and physiological responses of two hybrid poplar clones to ozone

Functional Leaf Traits and Diurnal Dynamics of Photosynthetic Parameters Predict the Behavior of Grapevine Varieties Towards Ozone

A comparative study on functional leaf treats and the diurnal dynamics of photosynthetic processes was conducted on 2-year-old potted plants of two grape (Vitis vinifera L.) varieties (Aleatico, ALE, and Trebbiano giallo, TRE), exposed under controlled conditions to realistic concentrations of the pollutant gas ozone (80 ppb for 5 h day^-1, 8:00–13:00 h, + 40 ppb for 5 h day^-1, 13:00–18:00 h). At constitutive levels, the morphological functional traits of TRE improved leaf resistance to gas exchange, suggesting that TRE is characterized by a potential high degree of tolerance to ozone. At the end of the treatment, both varieties showed typical visible injuries on fully expanded leaves and a marked alteration in the diurnal pattern of photosynthetic activity. This was mainly due to a decreased stomatal conductance (-27 and -29% in ALE and TRE, in terms of daily values in comparison to controls) and to a reduced mesophyllic functioning (+33 and +16% of the intercellular carbon dioxide concentration). Although the genotypic variability of grape regulates the response to oxidative stress, similar detoxification processes were activated, such as an increased content of total carotenoids (+64 and +30%, in ALE and TRE), enhanced efficiency of thermal energy dissipation within photosystem II (+32 and +20%) closely correlated with the increased de-epoxidation index (+26 and +22%) and variations in content of some osmolytes. In summary, we can conclude that: the daily photosynthetic performance of grapevine leaves was affected by a realistic exposure to ozone. In addition, the gas exchange and chlorophyll a fluorescence measurements revealed a different quali-quantitative response in the two varieties. The genotypic variability of V. vinifera and the functional leaf traits would seem to regulate the acclimatory response to oxidative stress and the degree of tolerance to ozone. Similar photoprotective mechanisms were activated in the two varieties, though to a different extent.

Responses of evergreen and deciduous Quercus species to enhanced ozone levels

Plants of one evergreen oak (Quercus ilex) and three deciduous oaks (Q. faginea, with small leaves; Q. pyrenaica and Q. robur, with large leaves) were exposed both to filtered air and to enhanced ozone levels in Open-Top Chambers. Q. faginea and Q. pyrenaica were studied for the first time. Based on visible injury, gas exchange, chlorophyll content and biomass responses, Q. pyrenaica was the most sensitive species, and Q. ilex was the most tolerant, followed by Q. faginea. Functional leaf traits of the species were related to differences in sensitivity, while accumulated ozone flux via stomata (POD1.6) partly contributed to the observed differences. For risk assessment of Mediterranean vegetation, the diversity of responses detected in this study should be taken into account, applying appropriate critical levels.

Gas exchange, antioxidants and foliar injuries in saplings of a tropical woody species exposed to ozone

Ozone (O(3)) reaches phytotoxical concentrations in the tropics, but the sensitivity of tropical plant species to O(3) remains unknown. Visible foliar injuries, carbon assimilation (A(sat)), stomatal conductance, superoxide dismutase enzyme (SOD) activity and ascorbic acid concentration (AA) were evaluated in different-aged leaves of Psidium guajava 'Paluma' saplings. We hypothesized that the old leaves are less capable of combating the stress induced by O(3) and hence exhibit more severe leaf injuries. Three O(3) exposure experiments were performed with 'Paluma' saplings in sites with high O(3) concentration and also under filtered air conditions. The exposure experiments corresponding to the seasons spring/2006, summer and autumn/2007. The decrease of A(sat) was greater in old leaves of saplings exposed to O(3), except in the second experiment, when the AA concentrations were more pronounced than in the other experiments. In second experiment, O(3) uptake was similar to that of the first experiment, but the injuries were less severe, probably due to the high AA concentrations. It was not possible to identify a pattern of superoxide dismutase enzyme (SOD) activity due to the high variability in the results from O(3) exposed and reference saplings. O(3) uptake/A(sat) was higher in leaves exhibiting greater injury, suggesting that decrease in A(sat) may have been the main feature associated with the visible foliar symptons.

Phenogenetic response of silver birch populations and half-sib families to elevated ozone and ultraviolet-B radiation at juvenile age

Phenogenetic response of silver birch populations and half-sib families to separate and combined elevated ozone (O(3)) concentrations and ultraviolet-B (UV-B) radiation dozes was studied at juvenile age in the climatic chambers. Significant population and family effects were found for seedling height, lamina width, and leaf damage. The exposure to UV-B radiation decreased genetic variation at the stage of seed germination. Complex exposure to UV-B and O(3) caused an increase of genetic variation at the stage of intensive seedling growth: seedling height genetic variation in separate treatments increased from 23.7-38.6 to 33.7-65.7%, the increase for lamina width was from 10.2-13.9 to 13.6-31.8%. Different populations and families demonstrated differing response to elevated complex UV-B and O(3) exposure. Changes of genetic intra-population variation were population-specific. Such changes in genetic variation under the impact of stressors can alter adaptation, stability, and competitive ability of regenerating populations in a hardly predictive way.

Stomatal characteristics and infection biology of Pyrenopeziza betulicola in Betula pendula trees grown under elevated CO2 and O3

Two silver birch clones were exposed to ambient and elevated concentrations of CO(2) and O(3), and their combination for 3 years, using open-top chambers. We evaluated the effects of elevated CO(2) and O(3) on stomatal conductance (g(s)), density (SD) and index (SI), length of the guard cells, and epidermal cell size and number, with respect to crown position and leaf type. The relationship between the infection biology of the fungus (Pyrenopeziza betulicola) causing leaf spot disease and stomatal characteristics was also studied. Leaf type was an important determinant of O(3) response in silver birch, while crown position and clone played only a minor role. Elevated CO(2) reduced the g(s), but had otherwise no significant effect on the parameters studied. No significant interactions between elevated CO(2) and O(3) were found. The infection biology of P. betulicola was not correlated with SD or g(s), but it did occasionally correlate positively with the length of the guard cells.

Ozone uptake (flux) as it relates to ozone-induced foliar symptoms of Prunus serotina and Populus maximowiziixtrichocarpa

Field studies were conducted during 2003 and 2004 from early June to the end of August, at 20 sites of lower or higher elevation within north-central Pennsylvania, using seedlings of black cherry (Prunus serotina, Ehrh.) and ramets of hybrid poplar (Populus maximowiziixtrichocarpa). A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance. The most significant factors explaining stomatal variance were tree species, air temperature, leaf vapor pressure deficit, elevation, and time of day. Overall, environmental factors explained less than 35% of the variation in stomatal conductance. Ozone did not affect gas exchange rates in either poplar or cherry. Ozone-induced foliar injury was positively correlated with cumulative ozone exposures, expressed as SUM40. Overall, the amount of foliar injury was better correlated to a flux-based approach rather than to an exposure-based approach. More severe foliar injuries were observed on plants growing at higher elevations.

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0-5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (psi(L)) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (g(wv)) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (P(n)), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g(wv) and P(n) demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.

Responses of hybrid poplar clones and red maple seedlings to ambient O(3) under differing light within a mixed hardwood forest

The responses of ramets of hybrid poplar (Populus spp.) (HP) clones NE388 and NE359, and seedlings of red maple (Acer rubrum, L.) to ambient ozone (O(3)) were studied during May-September of 2000 and 2001 under natural forest conditions and differing natural sunlight exposures (sun, partial shade and full shade). Ambient O(3) concentrations at the study site reached hourly peaks of 109 and 98 ppb in 2000 and 2001, respectively. Monthly 12-h average O(3) concentrations ranged from 32.3 to 52.9 ppb. Weekly 12-h average photosynthetically active radiation (PAR) within the sun, partial shade and full shade plots ranged from 200 to 750, 50 to 180, and 25 to 75 micromol m(-2) s(-1), respectively. Ambient O(3) exposure induced visible foliar symptoms on HP NE388 and NE359 in both growing seasons, with more severe injury observed on NE388 than on NE359. Slight foliar symptoms were observed on red maple seedlings during the 2001 growing season. Percentage of total leaf area affected (%LAA) was positively correlated with cumulative O(3) exposures. More severe foliar injury was observed on plants grown within the full shade and partial shade plots than those observed on plants grown within the sun plot. Lower light availability within the partial shade and full shade plots significantly decreased net photosynthetic rate (Pn) and stomatal conductance (g(wv)). The reductions in Pn were greater than reductions in g(wv), which resulted in greater O(3) uptake per unit Pn in plants grown within the partial shade and full shade plots. Greater O(3) uptake per unit Pn was consistently associated with more severe visible foliar injury in all species and/or clones regardless of differences in shade tolerance. These studies suggest that plant physiological responses to O(3) exposure are likely complicated due to multiple factors under natural forest conditions.

Influence of light fleck and low light on foliar injury and physiological responses of two hybrid poplar clones to ozone

Five-month old hybrid poplar clones NE388 and NE359 were exposed to square-wave 30, 55, and 80 ppb O(3) (8 h/day, 7 day/week) under constant high light (HL) and light fleck (LF) during 28 May-29 June 1999, and exposed to 30 and 55 ppb O(3) under HL, LF, and constant low light (LL) during 22 May-28 June 2000 within Continuously Stirred Tank Reactors (CSTR) in a greenhouse. Ramets of these two hybrid clones received similar total photosynthetically active radiation (PAR) within the LF and LL treatments. Visible foliar symptoms, leaf gas exchange, and growth were measured. More severe O(3) induced foliar symptoms were observed on ramets within the LF and LL treatments than within the HL treatment for both clones. The LF treatment resulted in significantly greater foliar injury than the LL treatment for NE388. The LF and LL treatments generally resulted in lower photosynthetic rates (Pn) for both clones, but did not affect stomatal conductance (g(wv)); therefore, the ratios of g(wv)/Pn and the O(3) uptake/Pn were greatest in plants grown under the LF treatment, followed by those grown under LL treatment; plants grown under HL had the lowest ratios of g(wv)/Pn and O(3) uptake/Pn. Greater ratios of g(wv)/Pn and O(3) uptake/Pn were consistently associated with more severe visible foliar symptoms. The negative impacts of the LF treatment on growth were greater than those of the LL treatment. Results indicate that not only the integral, but also the pattern of photo flux density, may affect carbon gain in plants. Increased foliar injury may be expected under light fleck conditions due to the limited repair capacity as a result of continuity of O(3) uptake while photosynthesis decreases under LL conditions.