Plant responses to elevational gradients of O(3) exposures in Virginia

In Shenandoah National Park, O(3) monitoring data were characterized and attempts were made to relate O(3) concentration levels to visible foliar injury observed for five plant species surveyed. Foliar injury for three species increased with elevation. The 24-h monthly mean O(3) concentrations tended to increase with elevation; however, the number of elevated hourly occurrences did not. Although the frequency of high hourly O(3) concentrations did not consistently increase with elevation, O(3) exposures in the park may have been high enough to provoke an effect that may have been enhanced by vegetation sensitivities that differed as a function of altitude.

Response of radish to multiple stresses: I. Physiological and growth responses to changes in ozone and nitrogen

Experiments were conducted to determine the impact of nitrogen and ozone (O₃ ) stress on the growth of domestic radish Raphanus sativus L. cv. Cherry Belle. Plants were grown in field chambers with sub-, optimal and supra-optimal levels of nitrogenous fertilizer. Chamber air was either charcoal-filtered, or supplemented with one of two levels of O₃ . The highest O₃ treatment resulted in significant reduction in weight of hypocotyls and roots while elevated nitrogen treatments resulted in increased weight of all plant parts. Ozone did not affect the weight of plant foliage at any nitrogen level. Plants grown with lower levels of nitrogen had less leaf biomass but the tissue accounted for a greater percentage total weight than did the foliage of higher nitrogen treatments. Relative growth rate of whole plants was not affected by O₃ or nitrogen treatments reflecting compensation in response to both stresses. Ozone-induced depression in biomass was observed in O₃ -treated plants grown with higher nitrogen supply but not in those grown with limiting nitrogen. This observation could reflect compensation at the lower levels of nitrogen supply or inability to detect changes in biomass due to reduced weights of plants grown at the lowest nitrogen supply. The dry weight ratio of sink organs (hypocotyl plus root)/shoot was significantly correlated with the total non-structural carbohydrate (TNC) content of these organs, regardless of treatment. Initially, O₃ induced a significant decrease and nitrogen an increase in percent TNC of sink organs. At later sampling times, plants adjusted to stress as effects on percent TNC were no longer evident.

Gas exchange and SO2 fumigation studies with irrigated and unirrigated field grown Diplacus aurantiacus and Heteromeles arbutifolia

Experiments were performed on an evergreen (Heteromeles arbutifolia) and a drought deciduous shrub (Diplacus aurantiacus) to determine, 1) whether approaches for evaluating SO₂ absorption by leaves in laboratory studies could be extended to field studies, 2) the effects of irrigation on metabolism and SO₂ responses of the study species during a season when water was limiting, 3) to interpret SO₂ responses on the basis of SO₂ flux rates. Laboratory-developed approaches for evaluating SO₂ absorption by leaves were found to be suitable for use with field plants, despite field plants having lower gas exchange rates. Supplementing water during times of deficit did not override all the biological and environmental factors that limited photosynthesis (A). Irrigation increased leaf longevity of D. aurantiacus, and stomatal conductance to water vapour (g); g was also shown to increase with H. arbutifolia on irrigation. Irrigation profoundly influenced plant response to SO₂. Unwatered D. aurantiacus had only a small g and therefore a reduced capacity to absorb SO₂ and respond to SO₂; which resulted in apparent SO₂ avoidance. Water availability and SO₂ both affect g and therefore, SO₂ flux rates into the mesophyll. Different ambient SO₂ concentrations of 8.3 and 26.2 μmol m^-3 (0.2 and 0.6 ppm) were both found to result in similar SO₂ flux rates into the leaf, due to variations in g in response to water availability. Changes in g did not always result in changes in A, implying that carbon fixation may be little affected by some SO₂ exposures, although still potentially affecting such processes as maintenance of leaf water potential, transpirational cooling and nutrient uptake.

Screening loblolly pine seedling responses to SO2 and O3: analysis of families differing in resistance to fusiform rust disease

Open pollinated families of loblolly pine differing in resistance to fusiform rust disease were screened in laboratory studies for responses to gaseous air pollutants. Twenty families were given acute exposures (2 fumigations for 4 h each) to SO(2) (0.4-1.0 ppm), O(3) (0.25 ppm), SO(2) (0.4-1.0 ppm) + O(3) (0.25 ppm) and control. Analyses of variance were performed to evaluate the treatment effects of these air pollutants on percent foliar injury, and to determine whether the families responded differentially to the air pollution treatments. Treatment effects were significant, with the combination treatment of SO(2) + O(3) producing a higher percentage of foliar injury than the controls; however, injury levels were very low and may not be of biological significance. Subsequently, twelve families were grown in two soil types for exposure to chronic levels of SO(2) (0.06 ppm), O(3) (0.07 ppm), SO(2) (0.06 ppm) + O(3) (0.07 ppm) and control. The families were then ranked for decreased primary shoot growth, shoot dry weight, root dry weight, total plant dry weight and root/shoot ratio after exposure to air pollution treatments. Air pollution treatments as a main effect were significant for only one of five growth parameters measured, that of primary shoot growth. The main effect of family, and the interaction of family and air pollution treatments, were significant for most growth parameters measured. In general, O(3) alone and in combination with SO(2) reduced growth more than SO(2) alone. Fumigation with O(3) reduced growth of two families in comparison with control groups, whereas SO(2) alone produced decreased growth in one family and stimulated growth in three families. Treatment with O(3) alone produced higher root/shoot ratios than fumigation with charcoal-filtered air in two families. Overall, families which were fast growers under control conditions maintained their ranking after exposure to air pollution. Families producing less growth in charcoal-filtered air also produced less growth under various air pollution regimes. Results indicated that these families exhibited a high degree of resistance to air pollution injury. Growth responses of seedlings may not reflect family differences in long-term productivity. No relationship was apparent between fusiform rust resistance and growth reductions due to air pollutants.

Responses of Hawaiian Plants to Volcanic Sulfur Dioxide: Stomatal Behavior and Foliar Injury

Hawaiian plants exposed to volcanic sulfur dioxide showed interspecific differences in leaf injury that are related to sulfur dioxide-induced changes in stomatal condutance. Species with leaves that did not close stomata developed either chlorosis or necrosis, whereas leaves of Metrosideros collina closed stomata and showed no visual symptoms of sulfur dioxide stress.

Respiration in Relation to Adenosine Triphosphate Content during Desiccation and Rehydration of a Desiccation-tolerant and a Desiccation-intolerant Moss

O(2) consumption by the desiccation-tolerant moss Tortula ruralis and the desiccation-intolerant Cratoneuron filicinum increased markedly during the latter stages of desiccation. ATP content of the mosses during desiccation was not correlated with O(2) consumption, but was influenced by the rate at which the mosses lost water. The more rapid the water loss, the more ATP that was present in the dry mosses. The pattern of O(2) consumption on rehydration also was influenced by the previous rate of desiccation. After rapid desiccation of T. ruralis O(2) consumption upon rehydration was considerably elevated, and for up to 24 hours. After very slow desiccation the elevation was small and brief. Normal O(2) consumption did not occur in C. filicinum after rapid desiccation, but did so within a few hours of rehydration after slower speeds of drying. ATP levels in T. ruralis returned to normal within 5 to 10 minutes of rehydration. In C. filicinum, increases in ATP were closely correlated with O(2) consumption. These observations are considered to be related to differential damage caused to mitochondria and to cellular integrity by different speeds of water loss. The desiccation-tolerant moss appears to be able to repair the severe damage imposed by rapid desiccation whereas the desiccation-intolerant moss cannot.