Left Injury Research Articles

Relationship between cereal leaf beetle (Coleoptera: Chrysomelidae) egg and fourth-instar populations and impact of fourth-instar defoliation of winter wheat yields in North Carolina and Virginia.

Cereal leaf beetle, Oulema melanopus (L.), has become a serious pest of small grains in the mid-Atlantic region of the United States. Existing thresholds for implementing control measures allowed too much leaf damage and consequent yield loss to occur before recommending treatment. Information on beetle biology and crop response to injury, both prerequisites for developing new management strategies, was lacking for this region. A 3-yr project was initiated to generate an area wide cereal leaf beetle biological and yield impact database for winter wheat, and to evaluate the injury and yield loss potential of different population densities. Over the study period, beetle populations were evaluated at 26 winter wheat field locations in Virginia and North Carolina. Eggs and larvae, classified to instar, were counted twice each week from February to June. Replicated insecticide versus noninsecticide treatments were conducted at each location where leaf defoliation and yield were documented. Results showed that the relationship between 50th percentile egg and fourth-instar population estimates were in strong agreement (y = 0.36x - 0.01; r2 = 0.79). Potentially detrimental larval infestations were forecast before appearance of foliage injury from egg populations present during the stem elongation to flag leaf emergence developmental stages. A significant positive linear relationship between total fourth instar per stem population estimates and percent flag leaf defoliation was detected (y = 20.29x + 1.34; r2 = 0.60). A weaker but still significant relationship between the total fourth-instar population estimates and percent yield loss was found (y = 11.74x + 6.51; r2 = 0.26), indicating that factors in addition to flag leaf injury, primarily by fourth instars, also contributed to reduced yields.

Differences of Betula origins in ozone sensitivity based on open-field experiment over two growing seasons

One-year-old seedlings of nine different white birch seed origins (Betula pendula Roth, Betula platyphylla Sukatchev var. japonica Hara, two crossings of plus trees of B. pendula, and five two-way hybrids between B. pendula, Betula resinifera Britt., and B. platyphylla) were exposed to ambient ozone (control) and 1.3 × ambient ozone concentrations over two growing seasons. At the end of each growing season, the plants were measured for leaf, stem and root growth; visible leaf injuries; leaf senescence; and ribulose 1,5-bisphosphate carboxylase-oxygenase, starch, soluble protein, chlorophyll, carotenoid, and nutrient concentrations to determine the differences in ozone sensitivity among these species and hybrids and the relationship of ozone sensitivity to changes in growth pattern and tolerance to other abiotic stresses. There was a large variation in growth among seedlings of different birches (species and hybrids). In most birches, elevated ozone exposure resulted in altered resource allocation at the expense of roots, leading to reduced root/shoot ratio. In fast-growing birches, stimulated stem height and foliage growth in the second growing season indicated compensatory growth, which was accompanied by accelerated senescence of old leaves. Seedlings of B. platyphylla and those from crossings with Finnish plus trees (bred for growth) showed highest susceptibility to ozone. The hybrids between Alaskan B. resinifera and Finnish B. pendula were intermediate in ozone sensitivity, whereas the hybrids between Japanese B. platyphylla and Finnish B. pendula genotypes were of improved tolerance compared with parents. The results suggest that ozone-induced disturbances in carbon allocation favouring shoot growth pose a real risk factor for birch establishment, production, and sustainable forestry because of potential deteriorating belowground processess and long-term tree vitality.

Supraoptimal Soil Temperatures Induced Oxidative Stress in Leaves of Creeping Bentgrass Cultivars Differing in Heat Tolerance

High temperature is a major factor limiting growth of cool‐season grasses during summer months. The objective of this study was to determine whether oxidative stress is involved in leaf injury induced by high soil temperatures in two creeping bentgrass (Agrostis palustris Huds.) cultivars, heat‐tolerant L‐93 and heat‐sensitive Penncross. Shoots and roots were exposed to four differential temperature regimes in growth chambers and water baths: (i) 20/20°C (control); (ii) 20/35°C (high soil temperature); (iii) 35/20°C (high air temperature); and (iv) 35/35°C (high shoot/soil temperatures). Turf quality, leaf photochemical efficiency (Fv/Fm), electrolyte leakage (EL), content of a lipid peroxidation product (malondialdehyde, MDA), and activities of the antioxidants superoxide dismutase (SOD) and catalase (CAT) were determined. Turf quality and leaf Fv/Fm ratio decreased, whereas EL and MDA contents increased under high soil temperature alone or in combination with high air temperature regimes in both cultivars, but to a greater extent in Penncross than in L‐93. Decreases in turf quality and Fv/Fm ratio and increases in EL and MDA were more pronounced at 20/35°C than at 35/20°C. The activities of SOD and CAT decreased with prolonged periods of high temperatures and to a greater extent for Penncross than for L‐93. The reductions in SOD and CAT activities were more severe at 20/35 than at 35/20°C. These results suggest that high soil temperature caused more severe oxidative damage to leaves than high air temperature by limiting antioxidant activities and inducing lipid peroxidation. This oxidative stress was associated with accelerated leaf senescence under high temperature conditions. Maintenance of antioxidant activities and low levels of lipid peroxidation was related to the better tolerance of creeping bentgrass to high soil temperature stress imposed on roots or high air temperature on shoots.

Antioxidant capacity is correlated with susceptibility to leaf spot caused by a rapid temperature drop in Saintpaulia (African violet)

The relationship between the susceptibility to rapid temperature drop induced leaf injury, i.e. “leaf spot”, and the antioxidant capacities of several Saintpaulia (African violet) cultivars was examined. Cultivars ‘Ritali’ and ‘Tamiko’, that are more susceptible to leaf spot caused by a rapid drop in leaf temperature from 30 to 15°C than are cultivars ‘Maui’ and ‘New Jersey’. The susceptible cultivars were also more susceptible to oxidative stress caused by H 2O 2 and active chlorine than the tolerant cultivars. Reduction of available chlorine, considered to be accelerated by antioxidants of leaf tissue, was rapid in ‘Maui’ and ‘New Jersey’. Activity of the antioxidant enzymes superoxide dismutase and catalase were higher in the leaves of ‘Maui’ and ‘New Jersey’ than in the susceptible cultivars. These findings show a correlation between leaf spot injury and antioxidant capacity in Saintpaulia leaves.

Interactive effects of boron and salinity stress on the growth, membrane permeability and mineral composition of tomato and cucumber plants

A greenhouse study was conducted in order to determine interactive effects of NaCl salinity and B on the growth, sodium (Na), chloride (Cl), boron (B), potassium (K) concentrations and membrane permeability of salt resistant Tomato (Lycopersicon esculentum L. cv. Lale F1) and salt sensitive cucumber (Cucumis sativus L. cv. Santana F1) plants. Plants were grown in a factorial combination of NaCl (0 and 30 mM for cucumber and 0 and 40 mM for tomato) and B (0, 5, 10 and 20 mg kg−1 soil). Boron toxicity symptoms appeared at 5 mg kg−1 B treatments in both plants. Salinity caused an increase in leaf injury due to B toxicity, but it was more severe in cucumber. Dry weights of the plants decreased with the increasing levels of applied B in nonsaline conditions, but the decrease in dry weights due to B toxicity was more pronounced in saline conditions especially in cucumber. Salinity × B interaction on the concentration of B in both plants was found significant. However, increase in B concentrations of tomato decreased under saline conditions when compared to nonsaline conditions. Contrary to this, B concentration of cucumber increased as a result of increasing levels of applied B and salinity. Salinity increased Na and Cl concentrations of both plants. Potassium concentration of tomato was not affected by salinity and B treatments, but K concentration of cucumber was decreased by salinity. Membrane permeability of the plants was increased by salinity while toxic levels of B had no effect on membrane permeability in nonsaline conditions. Membrane permeability was significantly increased in the presence of salinity by the increasing levels of applied B.

Ozone sensitivity in herbaceous species as assessed by direct and modulated chlorophyll fluorescence techniques

Summary Seven plant species were exposed in open-top chambers to four levels of ozone (O 3 ) during two growing seasons and screened for treatment effects on the fast chlorophyll a (Chl) fluorescence transient kinetics of dark-adapted leaves, and on the fluorescence signals obtained from the same leaves in illuminated steady-state. The aim was to identify the nature of O 3 effects on PSII, and to determine inter-specific differences. In dark-adapted leaves, O 3 caused a reduction in variable fluorescence (F V : F 0 ), indicating an overall reduction in the efficiency of primary photochemistry. A large increase in excitation energy dissipation per active reaction centre (DI 0 /RC) and a smaller increase in the trapping rate of excitons (TR 0 /RC), showed that a fraction of the reaction centres was inactivated while the rest sustained full functionality. The magnitude of the effect increased in the order of Bromus erectus Centaurea jacea Trisetum flavescens Rumex obtusifolius Plantago lanceolata Trifolium pratense Knautia arvensis . The inter-specific variability in PSII responses could not be explained solely by specific differences in modelled O 3 uptake by the leaves. Visible leaf injury was not related to changes in fluorescence emission. In illuminated steady-state, O 3 sensitivity was most expressed in the change in quantum yield of photosynthetic electron transport (Φ PSII ). The ranking of species differed from the ranking obtained in dark-adapted leaves. These results suggest that the mechanistic basis for O 3 effects on PSII is similar in all species, but that inter-specific differences exist in the magnitude of change which cannot be explained solely by different O 3 uptake rates. The observed changes in fluorescence signals are not O 3 -specific.

Differences of <i>Betula</i> origins in ozone sensitivity based on open-field experiment over two growing seasons

One-year-old seedlings of nine different white birch seed origins (Betula pendula Roth, Betula platyphylla Sukatchev var. japonica Hara, two crossings of plus trees of B. pendula, and five two-way hybrids between B. pendula, Betula resinifera Britt., and B. platyphylla) were exposed to ambient ozone (control) and 1.3 × ambient ozone concentrations over two growing seasons. At the end of each growing season, the plants were measured for leaf, stem and root growth; visible leaf injuries; leaf senescence; and ribulose 1,5-bisphosphate carboxylase-oxygenase, starch, soluble protein, chlorophyll, carotenoid, and nutrient concentrations to determine the differences in ozone sensitivity among these species and hybrids and the relationship of ozone sensitivity to changes in growth pattern and tolerance to other abiotic stresses. There was a large variation in growth among seedlings of different birches (species and hybrids). In most birches, elevated ozone exposure resulted in altered resource allocation at the expense of roots, leading to reduced root/shoot ratio. In fast-growing birches, stimulated stem height and foliage growth in the second growing season indicated compensatory growth, which was accompanied by accelerated senescence of old leaves. Seedlings of B. platyphylla and those from crossings with Finnish plus trees (bred for growth) showed highest susceptibility to ozone. The hybrids between Alaskan B. resinifera and Finnish B. pendula were intermediate in ozone sensitivity, whereas the hybrids between Japanese B. platyphylla and Finnish B. pendula genotypes were of improved tolerance compared with parents. The results suggest that ozone-induced disturbances in carbon allocation favouring shoot growth pose a real risk factor for birch establishment, production, and sustainable forestry because of potential deteriorating belowground processess and long-term tree vitality.

Mechanisms of salt stress tolerance in two rose rootstocks: Rosa chinensis ‘Major’ and R. rubiginosa

The responses of two rose rootstocks Rosa chinensis ‘Major’ and R. rubiginosa were investigated under salt stress. The distribution of chloride and sodium ions in all plant parts was determined. The salt treatments were applied through irrigation water containing 0, 5, 10, 20 and 30 mM NaCl. Necrosis on the leaves as a result of the NaCl treatments was observed with in rootstocks after two months. Leaf injury was more pronounced in R. chinensis ‘Major’ than R. rubiginosa. The rootstock R. rubiginosa showed a higher tolerance to the NaCl stress than R. chinensis ‘Major’. The survival of the plants under increased NaCl stress as well as the extent of leaf injury could be used in the determination of tolerance of the rose genotypes. The lower older leaves contained higher concentrations of Cl − than the young upper leaves. Leaf samples had higher concentrations of Cl − than stem samples taken from the same positions. The roots contained higher amounts of Cl − than the stem samples. The plants accumulated higher amounts of Cl − in comparison with Na +. The lower leaves of R. chinensis ‘Major’ had higher amounts of Na + than in all other parts whereas R. rubiginosa had higher concentrations of Na + in the roots than in all other parts.

Factors that Affect Development of Collar Rot on Tobacco Seedlings Grown in Greenhouses.

Collar rot, caused by Sclerotinia sclerotiorum, is an important disease of tobacco transplants produced under greenhouse conditions. Factors that affect the development of the disease were studied, including age of seedlings, presence of an external source of nutrients (leaf extract), clipping (leaf removal) practices, exposure to low temperature, and leaf injury caused by heat and a chemical. Flue-cured tobacco seedlings, cultivar K-326, were grown in polystyrene cell trays floating on a nutrient solution. Trays were maintained in a phytotron growth chamber with a 28/18°C day/night temperature regime. Seedlings were inoculated with ascospores of S. sclerotiorum at the desired stage of growth by placing mature apothecia in the growth chamber and inducing ascospore release and deposition. Disease incidence was determined by examining seedlings for the presence of stem lesions over the next 15 to 21days. Seedlings between 35 and 53 days old were more susceptible to collar rot than younger or older seedlings. Inoculum efficiency was highest and disease was most severe when an external source of nutrients was present on leaf surfaces. Clipping of leaf tips did not increase disease, but if the leaf pieces created by clipping were left on seedlings, collar rot development was enhanced compared with treatments where debris was removed. Heat and chemical injuries that resulted in necrotic tissue provided highly susceptible infection courts for ascospores of S. sclerotiorum, but exposure to low temperature, which caused no visible injury, did not enhance infection. Adoption of cultural practices that minimize accumulation of leaf debris and eliminate factors that cause necrotic injury on leaves should greatly reduce the severity of collar rot of tobacco seedlings.

Effect of calcium spray materials, rate, time of spray application, and rootstocks on fruit quality of ‘red’ and ‘golden delicious’ apples

Calcium (Ca) spray materials improved fruit quality as measured by control of bitter pit, fruit finish (appearance), increased red skin color, reduced incidence of scald, increased juiciness, texture, and fruit firmness of ‘Red’ and ‘Golden Delicious’ apples (Malus domestica, Borkh.). Concentrations of Ca in leaf and fruit tissues were increased by Ca sprays, especially calcium chloride (CaCl2)‐containing spray materials. Improved fruit firmness and control of bitter pit occurred for either standard recommended or high rates of Ca spray materials. At high rates of application, the only significant difference that occurred between early and late applications of Ca spray materials was that less leaf injury occurred with the early applications. Unsprayed ‘Red Delicious’ fruit from M.7 rootstocks had greater fruit peel Ca concentrations and a lower incidence of bitter pit but smaller fruit than fruit from trees on M.26 rootstocks. The above information is strong evidence that Ca sprays are important for the improvement of apple quality.

Visible and microscopic injury in leaves of five deciduous tree species related to current critical ozone levels

Because the current critical level of ozone (O3) for forest trees is based only on one species, the responses of five deciduous tree species were differentiated in a climate chamber experiment. The number of symptomatic leaves per tree was significantly increased, and stomatal conductance was decreased under 50% ambient+30 nl l−1 O3 as compared to ‘normal’ senescence at 50% ambient [O3]. Species with a high stomatal conductance did not show earlier or more leaf injury symptoms. The additional 30 nl l−1 O3 induced specific pectinaceous cell wall protrusions, phenolic cell wall incrustations, tonoplast vesicles, and inhomogeneous, condensed/precipitated phenolic material in the vacuoles. Due to added O3, cell senescence was accelerated with increased electron-density of the cytoplasm, and initial chloroplast degeneration. The slow degeneration process started in mesophyll cells, and expanded into epidermal and finally guard cells. Because of the large variance in biomass between individuals and species, the current critical level is supported by the assessment of visible leaf symptoms rather than growth reduction.

Response to ambient ozone of two white clover (Trifolium repens L.cv. “Regal”) clones, one resistant and one sensitive, grown in a Mediterranean environment

Two clones of white clover (Trifolium repens L.) differing in ozone tolerance were grown in southern Italy during 1997 and 1998 to study the effects of ambient ozone exposure on yield, leaf morphology and water use. Ambient ozone levels were high in both years with values exceeding the threshold for leaf injury reported in the literature. In both years ozone injury was observed on the sensitive clone (NC-S) but not on the resistant one (NC-R), and leaf and stolon dry matter production was significantly lower in NC-S than in NC-R. However, it cannot be excluded that other factors, such as high temperature, interacted with the effect of ozone on biomass production. The clones differed in morphological characteristics. Lower total leaf area in NC-S plants was due to a smaller number of leaves per plant, but the average area per leaf was higher in NC-S. Specific leaf weight and net assimilation rate were higher in the more productive clone (NC-R). Cumulative plant water use was higher in NC-R in each growth period because of the larger leaf area; by contrast, water use per unit leaf area was higher in NC-S, indicating higher leaf conductance to water vapour. The results suggest that ozone significantly reduces the yield of sensitive white clover plants under well-watered conditions, and that the difference in ozone tolerance between clover clones is related to differences in leaf morphology and water use.

Effects of sodium chloride on survival and stem elongation of two Asian pear rootstock seedlings

Survival, leaf burn, and mineral uptake of two Asian Pyrus rootstocks were evaluated under NaCl irrigation. Potted seedlings of 2-year-old pear rootstocks, Pyrus betulifolia Bunge (BET) and P. pyrifolia (Burm f.) Nakai (PYR) were irrigated with 0, 25, 50, 100, 150 or 200 (BET only) mM NaCl solution. BET showed high survival rate and slight leaf injury even under 100 mM NaCl irrigation. PYR however exhibited severe leaf injury and most of the tested plants died under 25 mM NaCl irrigation. Leaf Na concentration in BET subjected to 100 mM was similar to that of PYR at 25 mM.

Container-grown tree seedling responses to sodium chloride applications in different substrates

Seedlings of Norway maple ( Acer platanoides), silver birch ( Betula pendula), Norway spruce ( Picea abies) and Scots pine ( Pinus sylvestris) were grown in selected sodium chloride (NaCl) concentrations, soil types and under different watering regimes. Plants were raised from seeds, except for Scots pine plants which were obtained from a commercial source. Among the plant species tested, Scots pine was the most tolerant to soil salinity, while Norway spruce was the most susceptible. For both Norway maple and Norway spruce some half-sib families were more tolerant than others. No significant correlation was found between the tolerance of different half-sib families and the tolerance of mother trees observed in the field. The extent of leaf necrosis correlated significantly with the leaf concentrations of sodium (Na) and chloride (Cl). Among half-sib families within the species no such correlation was found. On the other hand, the least injured progeny of Norway maples had the highest concentrations of NaCl. The extent of salt-induced leaf necrosis varied with soil type, and a significant interaction between species and soil type was observed. Seedlings of Norway spruce grown in sand showed more severe necrosis and significantly higher concentrations of Na and Cl than seedlings grown in loam, silt loam, and peat. The severity of salt-induced leaf injury varied with the watering regime. Silver birch was the most affected species by drought and autumn watering treatments. Plants of silver birch subjected to drought showed increased leaf necrosis compared to the non-treated plants, and autumn watering treatment reduced the severity of leaf necrosis.

Yield response of pumpkin and winter squash to simulated cucumber beetle (Coleoptera: Chrysomelidae) feeding injury.

Field studies were conducted to characterize the yield responses of pumpkin, Cucurbita pepo L., and wintersquash, Cucurbita maxima Duch., to simulated striped cucumber beetle, Acalymma vittatum (F.), feeding damage. Preliminary studies in pumpkin ('Spookie') were conducted in 1993, and more complete studies in 1994 and 1995 in pumpkin (Spookie), and in 1995 and 1996 in winter squash ('Waltham'). Plants were artificially injured 1 time at the cotyledon, 1st, 2nd, or 3rd true leaf stages by clipping specified percentages of leaf area from all leaves on the plant. Treatments consisted of a control treatment with no simulated injury and 4 levels of simulated injury. Pumpkin treatments were 10, 20, 40, and 80% leaf area removal in 1993 and 1994 and 20, 40, 60, and 80% in 1995. Winter squash treatments were 20, 40, 60, and 80% leaf area removal in 1995, and 10, 20, 40, and 80% in 1996. In 1993, 5 wk after planting, mean leaf, stem, and total dry weight were significantly lower on pumpkin plants subjected to > or = 20% simulated leaf injury regardless of the growth stage when the injury occurred. Injury at the 3rd leaf stage resulted in a significant reduction in the mean leaf and total dry weight of plant, across all levels of injury. At 2-3 wk before crop maturity, fruit weight and number of fruit per plant were significantly lower with 80% leaf area removal. In 1994 and 1995, and when pumpkins were grown to full maturity and apparently able to compensate for the simulated damage, neither number nor weight of marketable fruit per plant were affected significantly by simulated injury at any stage of development nor level of simulated injury. In contrast, > or = 20% and 80% leaf area removal to winter squash resulted in significant reductions in the weight of marketable fruit and/or number of marketable fruit, in 1995 and 1996, respectively. The results of this study indicate that pumpkins can tolerate relatively high levels of simulated defoliation, whereas winter squash is less tolerant. Variable results across years in winter squash may indicate an interaction between injury and plant stress caused by abiotic factors such as soil moisture availability.

Tolerância da cultivar de soja coodetec 201 aos herbicidas inibidores de als

A obtenção de cultivares resistentes aos herbicidas possibilita o aumento da diversidade dos herbicidas utilizados seletivamente para o controle de plantas daninhas em uma determinada cultura. O aumento da disponibilidade destes herbicidas na cultura da soja pode proporcionar maior facilidade no controle de plantas daninhas de difícil eliminação, de espécies com características biológicas semelhantes à cultura e de plantas daninhas resistentes aos herbicidas. O objetivo deste trabalho foi avaliar a resistência cruzada da cultivar COODETEC 201 a três herbicidas inibidores da ALS, não seletivos para a cultura da soja. O experimento foi realizado em casa de vegetação através da semeadura em vasos, o qual foi disposto em delineamento completamente casualizado em arranjo fatorial. Os tratamentos constaram das cultivares de soja COODETEC 201 e OCEPAR 14 e dos herbicidas imazapyr, metsulfuron e nicosulfuron, aplicados em cinco doses. A aplicação destes produtos foi realizada 30 dias após a emergência, quando as plantas de soja estavam no estádio V4. A área foliar e a fitoxicidade aos 14 e 35 dias após a aplicação do herbicida metsulfuron foram menos afetadas na cultivar COODETEC 201 do que na OCEPAR 14. A determinação da restrição do crescimento das plantas em função da matéria seca das plantas demonstrou que as duas cultivares são igualmente sensíveis ao herbicida imazapyr. A cultivar COODETEC 201 apresentou maior tolerância aos herbicidas metsulfuron e nicosulfuron, sendo 10,25 e 3,25 vezes, respectivamente, mais resistente do que a cultivar OCEPAR 14.

Phytotoxicity of urea and biuret sprays to apple foliage

The effect of urea and biuret on leaf burn was investigated. Urea and biuret were applied as foliar sprays in factorial combinations at the rates of 0,1, and 2% (w/v) and 0,0.05,0.1, and 0.15% (w/v), respectively, in late April to 2‐year‐old ‘Braeburn'/'Malling‐Merton 111’ ('MM. 111') apple (Malus domestica Borkh.) trees in a greenhouse. The experiment was repeated in the field in late May and in August using 11‐year‐old ‘Golden Delicious'/'Malling 7A’ ('M.7A'). In August, additional urea [4% (w/v)] and biuret [0.4% (w/v)] treatments were applied. Biuret alone at all rates did not cause leaf damage. Within the range of concentrations used, urea was largely responsible for leaf burn and chlorosis following foliar sprays. However, presence of both chemicals in the spray solution increased leaf injury in April, but not at the later applications. Growers should use low‐biuret urea within reasonable costs.

Responses of Boreal Plants to High Salinity Oil Sands Tailings Water

AbstractIn the extraction of bitumen from oil sands ore, large volumes of railings water (CT water) containing elevated levels of Na, sulfate, bicarbonate and chloride are produced. High salinity process waters will probably affect terrestrial reclamation options. The present study tested the impact of tailings waters on boreal forest species including aspen (Populus tremuloides Michx.), buffalo berry [Sheperdia canadensis (L.) Nutt], northwest hybrid poplar (Populus deltoides × Populus balsamifera), dogwood (Cornus stolonifera Michx.), jack pine (Pinus banksiana Lamb.), and white spruce [Picea glauca (Moench) Voss]. Seedlings were grown in solution culture containing mineral nutrients and different dilutions of CT water, with and without supplemental salts (Na2SO4 and NaCl). After 4 wk of treatment, dogwood, hybrid poplar, and buffalo berry showed relatively high resistance to saline CT waters. Conifer seedlings developed leaf necrosis in all treatments, while aspen seedlings rapidly lost their foliage and produced new leaves. In comparison to the controls, elevated Na levels were measured in plant tissue of all species grown in CT water. However, some differences between species were observed, with jack pine seedlings showing much higher Na content than aspen, dogwood, or hybrid poplar. In hybrid poplar, the accumulation of Na was accompanied by a significant reduction in K, Mg, Ca, and P. Buffalo berry, aspen, jack pine, and white spruce showed elevated levels of S after growth in the sulfate‐enriched CT waters. High tissue Na content did not induce leaf injury in dogwood, hybrid poplar and buffalo berry, suggesting possible Na resistance.

Effect of packaging treatments and vacuum-cooling on quality of winter harvested iceberg lettuce

Heads of winter harvested iceberg lettuce ( Lactuca sativa L. cv. Coolguard) individually packed or sealed in perforated (22 μm thickness) or unperforated (25, 30 or 40 μm thickness) polypropylene films were stored up to 2 weeks at 2°C (storage period) and then held for 2.5 days at 12°C (shelf-life period). Five packaging treatments together with passive or active modification of the atmosphere within the package were applied. Vacuum-cooling was superimposed on these five treatments. Weight loss, wilting, physiological disorders, bacterial decay and quality were monitored. In all treatments, both slight severity of pink rib and russet spotting occurred. Brown stain and heart leaf injury were only detected on heads in unperforated bags. Low oxygen was generally related to a high quality score. Passive MAP in 40 μm PP and active (initial 5% O 2 and 0% CO 2) MAP in 30 μm PP were the best treatments for overall visual quality. Vacuum-cooling reduced both pink rib and heart-leaf injury but the effect only showed up during shelf-life period.

Interactions of chronic exposure to elevated CO2 and O3 levels in the photosynthetic light and dark reactions of European beech (Fagus sylvatica)

Young trees of European beech (Fagus sylvatica) acclimated for one growing season to ambient (c. 367 μl l−1) or elevated CO2 levels (c. 660 μl l−1) were exposed during the subsequent year to combinations of the same CO2 regimes and ambient or twice‐ambient ozone (O3) levels (generated from the database of a rural site). By the end of June, before the development of macroscopic leaf injury, the raised O3 levels had not affected the light and dark reactions of photosynthesis. However, acclimation to elevated CO2 had resulted in lowered chlorophyll and nitrogen concentrations, whereas photosynthetic performance, examined over a wide range of parameters from light and dark reactions, remained unchanged or showed only slight reductions (e.g. apparent electron transport rate, ETR; apparent quantum yield of CO2 gas exchange, ΦCO2; apparent carboxylation efficiency, CE; and photosynthetic capacity at light and CO2 saturation, PC). In August, after the appearance of leaf necroses, plants grown under ambient CO2 and twice‐ambient O3 conditions declined in both the photosynthetic light reactions (optimum electron quantum yield, Fv/Fm, non‐photochemical energy quenching, NPQ, reduction state of QA, apparent electron quantum yield, ΦPSII, maximum electron transport rates) and the dark reactions as reflected by CE, ΦCO2, as well as the maximum CO2 uptake rate (i.e. PC). CE, ΦCO2 and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO2 and O3 levels. By contrast, plants exposed to twice‐ambient O3 and elevated CO2 levels maintained a photosynthetic performance similar to individuals grown either under ambient CO2 and ambient O3, or elevated CO2 and ambient O3 conditions. The long‐term exposure to elevated CO2 therefore tended to counteract adverse chronic effects of enhanced O3 levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed.