Relationships of leaf diffusion resistance of Populus clones to leaf water potential and environment.

Leaf diffusion resistance (r 1) of the upper and lower leaf surfaces of several Populus clones was related to leaf water potential (ψ1), light intensity, vapor pressure deficit (VPD), and temperature by intrinsicallylinear, logarithmic multiple regression analyses. Regression equations accounted for up to 80% of variation in r 1 data. Light intensity and VPD varied among clones in importance in influencing r 1. Pronounced sensitivity of r 1 of certain clones to VPD was related to drought resistance in their parentage. Increasing r 1 was significantly positively correlated with ψ1, in apparent contradiction to prevailing concepts of stomatal response to water status, and this relationship was probably attributable to effects of other environmental variables on ψ1 and r 1. Leaf resistance decreased after a storm characterized by winds in excess of 160 km·h-1. Cuticular disruption and altered stomatal response may have been responsible for the storminduced r 1 decrease.

Relative sensitivity of three species of woody plants to SO2 at high or low exposure temperature.

Seedlings of paper birch (Betula papyrifera Marsh.), green ash (Fraxinus pennsylvanica Marsh.), and red pine (Pinus resinosa Ait.) fumigated with 0.2 ppm SO2 for 30 h at 30° C had higher leaf diffusive conductances (LDC) and absorbed more sulfur than seedlings fumigated at 12° C. Comparisons among the three species fumigated at the same temperature, however, do not support the view that a plant with higher LDC should absorb more SO2 than a plant with lower LDC. Mean relative growth rates ([Formula: see text]) of seedlings grown at 21° C after fumigation were variously affected by SO2. [Formula: see text] of green ash was not inhibited by SO2, but [Formula: see text] of roots of red pine seedlings was reduced by SO2, with greater inhibition in seedlings fumigated at 30° C. Root and shoot [Formula: see text] of paper birch seedlings were lowered by SO2, and effects of SO2 were about equal at both exposure temperatures. The data indicate that temperature can affect mechanisms of SO2 avoidance, tolerance, or both to various degrees in different species. Thus generalizations on the influence of exposure temperature on resistance of plants to SO2 may be inappropriate.

The role of stomata in sensitivity of Betula papyrifera seedlings to SO2 at different humidities.

Stomata of paper birch (Betula papyrifera Marsh.) seedlings were more open at high humidity than at low humidity and responded rapidly to changes in vapor pressure deficit. SO2 at 0.2 or 0.8 µl l-1 caused partial stomatal closure. Seedlings fumigated with SO2 at 0.2 or 0.5 µl l-1 for 30 h or 0.2 µl l-1 for 75 h took up more SO2 at high than at low humidity. Differences in pollutant uptake could be explained by stomatal conductance with no need to invoke changes in mesophyll conductance. Betula seedlings were more sensitive to SO2 when fumigated at high humidity, as manifested in more leaf necrosis, increased leaf abscission, and greater growth inhibition compared to seedlings fumigated at low humidity. Amount of injury to leaves increased with rate of SO2 uptake, and inhibition of root growth increased with total SO2 uptake.

Effects of flooding on Eucalyptus camaldulensis and Eucalyptus globulus seedlings.

Flooding for up to 40 days induced morphological changes and reduced growth of 6-week-old Eucalyptus camaldulensis and Eucalyptus globulus seedlings. However, the specific responses to flooding varied markedly between these species and with duration of flooding. Both species produced abundant adventitious roots that originated near the tap root and original lateral roots, but only E. camaldulensis produced adventitious roots on submerged portions of the stem. Flooding induced leaf epinasty and reduced total dry weight increment of seedling of both species but growth of E. globulus was reduced more. In both species dry weight increment of shoots was reduced more than dry weight increment of roots, reflecting compensatory growth of adventitious roots. Adaptation to flooding appeared to be greater in E. camaldulensis than in E. globulus. the importance of formation of adventitious roots in flooding tolerance is emphasized.

Stomatal response of populus clones to light intensity and vapor pressure deficit.

Responses of stomata of clones of Populus candicans Ait. x P. berolinensis Dipp. and Populus deltoides Bartr. x P. caudina (Ten.) Bugala to two levels of light intensity and vapor pressure deficit were studied in controlled environments. Significant stomatal responses to light and vapor pressure deficit were observed. Interactive effects of low light intensity and high vapor pressure deficit elicited greater stomatal closure than was obtained under low light or high vapor pressure deficit alone, indicating adaptation for increased water use efficiency under conditions unfavorable for photosynthesis relative to transpiration. Adaxial stomata of both clones were more sensitive than abaxial stomata to changing vapor pressure deficit and light intensity. Stomatal response to vapor pressure deficit appeared to be independent of bulk leaf water status. Stomata of P. candicans x P. berolinensis were more sensitive than stomata of P. deltoides x P. caudina to a change in vapor pressure deficit and less sensitive to a change in light intensity. The sensitivity of stomata of P. candicans x P. berolinensis to vapor pressure deficit may be related to drought resistance in its parentage (P. berolinensis).

Mobilization and Incorporation of Photoassimilated C by Growing Vegetative and Reproductive Tissues of Adult Pinus resinosa Ait. Trees.

Variations in translocation and incorporation of (14)C-labeled photosynthate in actively growing vegetative and reproductive tissues of 20-year-old Pinus resinosa trees with time were investigated. Five hours after exposure of 1-year-old needles on second order branches to (14)CO(2), 90% of the recoverable activity was still in the needles. The 1-year-old bark showed a small amount of activity, but terminal sinks had accumulated little (14)C. After 24 hours, activity in the 1-year-old needles decreased to 59% while actively growing terminal and lateral shoots and 2nd year cones had accumulated considerable tracer. Whereas activity in the 1-year-old bark increased, recovery from the 1-year-old wood was only 1.8%. After 1 week, relative activity in the 1-year-old needles had declined to 27%. Recovery of (14)C from various sinks was high and in the following order: 2nd year cones > terminal needles > lateral needles > terminal internode > lateral internodes > 1-year-old wood. Ninety per cent of the (14)C recovered after 5 hours was in the ethanol-soluble form, but by the end of 1 week only half was in the soluble fraction. Incorporation of tracer into insoluble compounds was high in expanding internodes and in 1-year-old xylem, and low in 2nd year cones. Total activity in the terminal internode generally declined toward the distal end while specific radioactivity increased. Only 5% of the (14)C recovered from cones was localized in developing seeds, but specific radioactivity of seeds was higher than in the cone scales and axis.

Growth Responses and Adaptations of Fraxinus pennsylvanica Seedlings to Flooding.

Flooding induced several physiological and morphological changes in Fraxinus pennsylvanica seedlings, with stomatal closure among the earliest responses. Subsequent changes included: reduction in dry weight increment of roots, stems, and leaves; formation of hypertrophied lenticels and production of adventitious roots on submerged portions of the stem above the soil line; leaf necrosis; and leaf abscission. After 15 days of stomatal closure as a result of flooding, stomata began to reopen progressively until stomatal aperture was similar in flooded and unflooded plants. Adventitious roots began to form at about the time stomatal reopening began. As more adventitious roots formed, elongated, and branched, the stomata opened further. The formation of adventitious roots was an important adaptation for flooding tolerance as shown by the high efficiency of adventitious roots in absorption of water and in high correlation between the production of adventitious roots and stomatal reopening.

Stomatal Conductance and Sulfur Uptake of Five Clones of Populus tremuloides Exposed to Sulfur Dioxide.

Plants of five clones of Populus tremuloides Michx. were exposed to 0, 0.2 or 0.5 microliter per liter SO(2) for 8 hours in controlled environment chambers. In the absence of the pollutant, two pollution-resistant clones maintained consistently lower daytime diffusive conductance (LDC) than did a highly susceptible clone or two moderately resistant clones. Differences in LDC among the latter three clones were not significant. At 0.2 microliter per liter SO(2), LDC decreased in the susceptible clone after 8 hours fumigation while the LDC of the other clones was not affected. Fumigation with 0.5 microliter per liter SO(2) decreased LDC of all five clones during the fumigation. Rates of recovery following fumigation varied with the clone, but the LDC of all clones had returned to control values by the beginning of the night following fumigation. Night LDC was higher in the susceptible clone than in the other clones. Fumigation for 16 hours (14 hours day + 2 hours night) with 0.4 microliter per liter SO(2) decreased night LDC by half. Sulfur uptake studies generally confirmed the results of the conductance measurements. The results show that stomatal conductance is important in determining relative susceptibility of the clones to pollution stress.

Ethylene, Ethane, Acetaldehyde, and Ethanol Production By Plants under Stress.

Red pine (Pinus resinosa Ait.) and paper birch (Betula papyrifera Marsh.) seedlings exposed to sulfur dioxide produced acetaldehyde and ethanol, and exhibited increased production of ethylene and ethane. Gas chromatographic measurement of head space gas from incubation tubes containing leaves or seedlings was a simple method of simultaneously measuring all four compounds. Increased ethylene production had two phases, a moderate increase from the beginning of the stress period and a large increase just prior to appearance of leaf lesions. Ethane production in SO(2)-stressed plants did not increase until lesions appeared. Acetaldehyde and ethanol production began within 6 hours at 0.3 microliter per liter SO(2) and 24 hours at 0.1 microliter per liter SO(2) and continued throughout a 6-day fumigation. Production of acetaldehyde and ethanol continued when plants were removed to clean air for up to 2 days. A higher concentration of SO(2) (0.5 microliter per liter) induced acetaldehyde and ethanol production within 2 hours of the start of fumigation of birch and pine seedlings. A number of other stresses, including water deficit, freezing, and ozone exposure induced production of acetaldehyde and ethanol. Production of these compounds was not due to hypoxia, as the O(2) partial pressure in the incubation vessels did not decline. Increasing the O(2) partial pressure to 300 millimeters Hg did not affect production of these compounds. Production of ethylene, acetaldehyde, and ethanol declined when more than 80% of the leaf area became necrotic, while ethane production was linearly related to the percentage of necrosis. A number of woody and herbaceous plant species produced acetaldehyde and ethanol in response to freezing stress, while others did not. Measurement of these four compounds simultaneously in the gas phase may be a valuable method for monitoring plant stress, particularly air pollution stress.

Effects of Phenylmercuric Acetate on Stomatal Movement and Transpiration of Excised Retula papyrifera Marsh. Leaves.

Effects of 10(-3)m, 10(-4)m, and 10(-5)m phenylmercuric acetate (PMA) on stomatal movement and transpiration of excised Betula papyrifera leaves were investigated. Duco cement leaf prints and transpiration decline curves were used for the analysis of stomatal condition. PMA induced stomatal closure and decreased transpiration. Stomata of leaves treated with any of the 3 PMA concentrations closed earlier and at a higher relative water content than did stomata of untreated leaves. As determined from transpiration decline curves, PMA at 10(-3)m caused an increase in apparent "cuticular" transpiration. However, the increase appeared to result largely from some PMA-poisoned stomata which remained open for prolonged periods. Considerable PMA toxicity was observed, with 10(-3)m and 10(-4)m concentrations causing browning of leaves. PMA treatment caused a decrease in chlorophyll content, even at a low PMA concentration (10(-5)m) which influenced stomatal response only slightly and did not cause evident browning of leaves. The time and degree of stomatal opening varied with stomatal size. Large stomata tended to open earlier and close later than small stomata. Hence, in Betula papyrifera stomata of various size classes were considered as physiologically different populations.