Experiments on the water balance of individual attached twigs of Picea abies (L .) Karst. in pure and ozone-enriched air

 Rates of transpiration and xylem sap flow were continuously measured in individual twigs in the upper crown of an 18-year-old spruce. Two gas exchange chambers were run simultaneously under identical conditions. One of two equivalent twigs was exposed to pure air whereas the other received the ozone-enriched air of the site. A third gas exchange chamber in mid-crown ran independently with normal outside air and was used for basic experiments. At certain times needles were sampled for water potential measurements. Chamber humidity was reduced step by step and the transpiration and xylem sap flow rates were permanently compared. It turned out that sap flow keeps up with transpiration without lagging as long as chamber humidity is high and the twigs outside the chamber are not subject to substantial evaporative demand. However, in warm summer weather and with high flow rates sap flow is no longer sufficient. As the balance quotient (uptake/release) of 0.8 was reached the stomata began to close and water balance improved. The flux quotient increased far above 1.0 without water potential of the needles, which had decreased before, increasing significantly. The balance quotient of the twig in ozone-enriched air fell to relatively low values and only increased again correspondingly slowly due to lagging stomatal closure. Despite increased water uptake after the light phase, the ozone-treated twig ran into a water deficit in the daily balance during the course of an uninterrupted drought period. Water deficit increased from day to day and only disappeared with the next rainfall. For providing insight into the ozone effect shown in this study it was thought necessary to discuss comprehensively the controversial views of the stomatal control mechanism. The results show that the stomata react to small scale changes in water status as expected for an effective negative feedback system. The less sensitive reaction of the stomata under the influence of ozone confirms earlier results. Increased severity and duration of the daily drought stress loads were attributed to a lag in adjustment due to poor stomatal control. The demonstrated function mechanism shows that the detrimental effect of ozone is dependent on weather conditions. Received: 12 April 1996 / Accepted: 24 June 1996     

Physiological responses of Fagus sylvatica L. exposed to low levels of ozone in open-top chambers

Four-year-old beech seedlings were fumigated with three levels of ozone for 2 consecutive years in open-top chambers. During the second growth season different physiological measurements were conducted before and during daily fumigation. A 25–40% decrease in net photosynthesis was seen during fumigation, whereas no differences were detected before fumigation in July. In August lasting effects in net photosynthesis were seen. The apparent quantum yield was decreased after fumigation. Stomatal conductance was generally decreased during fumigation, but transpiration was reduced relatively less than net photosynthesis indicating a lower water use efficiency of the trees exposed to ozone. Chlorophyll fluorescence (F_v/F_m) showed additive reductions in relation to ozone and light.     

Effects of air pollutants on the photosynthetic capacity of young Norway spruce trees. Response of single needle age classes during and after different treatments with O3, SO2, or NO2

Summary Potted young Norway spruce trees were exposed to different concentrations of the air pollutants ozone, sulphur dioxide and nitrogen dioxide under completely controlled environmental conditions. After the treatment, the potted trees were kept outdoors. Measurements of the maximum photosynthetic capacity (A₂₅₀₀) were performed with current-year and 1-year-old needles during and after exposure of the trees. In trees fumigated with nitrogen oxides no damage was found at the concentrations used, and the trees' ability to fix carbon dioxide was increased. Using SO₂, a rapid and marked decrease in A₂₅₀₀ was obtained within the first days of the experiment. This decrease did not continue further, but was reversed upon cessation of the fumigation. However, a clear dose-dependent decrease in A₂₅₀₀ occurred when trees were fumigated continuously with an ozone concentration of 450 nl l^–1 or more. The effect of ozone was not reversible, but continued during post-culture of the trees.     

Response of photosynthesis and cellular antioxidants to ozone in populus leaves

Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H₂O₂, etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides × Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone.     

Soil-plant-water aspects of ozone phytotoxicity in tomato plants

Summary Tomato (Lycopersicon esculentum Mill.) plants were grown in controlled environments and subjected to different soil water regimes. At 3-, 5-, and 7-leaf growth stages, plants were fumigated with ozone at 50 or 100 pphm for 1 h. Plants at 5- or 7-leaf stage were not as sensitive to ozone as were the young plants fumigated at 3-leaf stage. At the 7-leaf stage, leaf injury at nearoptimum water condition was very minimal, even at ozone concentration of 100 pphm. Ozone treatment decreased total dry matter of optimally watered plants fumigated at the 3-leaf stage. Plants subjected to water stress resulting in low leaf relative turgidity prior to ozone fumigation, were considerably protected from ozone phytotoxicity. Open stomata were an important factor in ozone phytotoxicity. Post-fumigation water regimes had no effect on eventual leaf injury. re]19720627     

Responses of selected birch (Betula pendula Roth) clones to ozone change over time

A long-term free air ozone fumigation experiment was conducted to study changes in physiological ozone responses during tree ontogeny and exposure time in ozone sensitive and tolerant clones of European white birch (Betula pendula Roth), originated from south and central Finland. The trees were grown in soil in natural microclimatic conditions under ambient ozone (control) and 1.4-1.7 x ambient (elevated) ozone from May 1996 to October 2001, and were measured for stem and foliage growth, net photosynthesis, stomatal conductance, stomatal density, visible injuries, foliar starch content and bud formation. After 6 years of exposure, the magnitude of ozone-induced growth reductions in the sensitive clone was 12-48% (significant difference), levels similar or greater than those reported earlier for 2- and 3-year-old saplings undergoing shorter exposures. In the tolerant clone, growth of these larger trees was reduced by 1-38% (significant difference in stem volume), although the saplings had previously been unaffected. In both clones, ozone stress led to significantly reduced leaf-level net photosynthesis but significantly increased stomatal conductance rates during the late summer, resulting in a lower carbon gain for bud formation and the onset of visible foliar injuries. Increasing ozone sensitivity with duration of exposure was explained by a change in growth form (relatively reduced foliage mass), a lower photosynthesis to stomatal conductance ratio during the late summer, and deleterious carry-over effects arising from the reduced number of over-wintering buds.     

A model for simulating transpiration of Eucalyptus salmonophloia trees

Understanding the water relations of Eucalyptus trees plays an important role in finding solutions to dryland salinity in southern Australia. A model for studying structure–function relationships in isolated tree crowns (radiation absorption, transpiration and photosynthesis, RATP) was parameterized to permit the seasonal transpiration course of a Eucalyptus salmonophloia tree to be quantified. Model responses to different parameterizations were tested in a sensitivity analysis. Predictive quality was mostly affected by the accuracy of information about leaf area density and stomatal responses to air vapor pressure deficit, and to a lesser extend by foliage dispersion. Assuming simple, non‐synergistic influences of changes in photosynthetic active radiation and air vapor pressure deficit on stomatal transpiration control, the model was able to simulate the daily water uptake of E. salmonophloia trees with reasonable predictive quality during an entire season. In order to more precisely simulate short‐term (i.e. diurnal) water use dynamics, the model must be extended to account for hydraulic and chemical controls of stomatal regulation of crown energy balance.     

The effects of ozone on growth and stomatal response in the F<Subscript>2</Subscript> generation of hybrid poplar (<Emphasis Type="Italic">Populus trichocarpa × Populus deltoides</Emphasis>)

Thirty-six F₂ hybrid poplar (Populus trichocarpa × P. deltoides) clones were fumigated with ozone to record its effects on growth, correlate them with stomatal response and screen for ozone sensitivity. Fumigation was applied for 6 to 9 h each day for approximately 3 months at ozone concentrations of 85 to 128 μg g⁻¹ using open-top chambers. Height, diameter, number of leaves, stomatal conductance, transpiration rate, total biomass, biomass components and root/shoot ratios were reduced by ozone stress. Percent of leaf fall in ozone-treated plants was nearly three times higher than in control plants exposed to charcoal-filtered air. Leaf senescence, because of ozone exposure, did not appear to be associated with reduced biomass production. Some clones had a high percentage of leaf-fall with ozone exposure, but were able to maintain total biomass production near that of the control. Their response may be an example of an ability to adjust or compensate for ozone damage. There was no significant or consistent relationship between stomatal conductance and total biomass or the change in stomatal conductance as a result of ozone exposure and the change in total biomass. Taken together, these results suggest that effects of ozone on poplar growth cannot be solely correlated to changes in stomatal conductance, more physiological and biochemical parameters should be examined.     

The effect of air pollution on the mechanism of stomatal control

Summary A long-term field experiment permanently measuring gas exchange in the top of a 70-year-old spruce, continued for through the 1990 growing season. Two gas exchange chambers were run simultaneously under identical climatic conditions. One of two similar twigs was exposed to ambient air whereas the other received pure air. These experiments aimed to examine the ability of the stomata to control water balance, comparing pure and ambient air. This was done not only in natural climatic conditions but also in experimental, specifically maintained stress situations. Special care was taken to ensure that only steady state values of stomatal responses are related to the environmental stimuli. During a drought period lasting several weeks, overshooting transpiration values were documented for the ambient air. The two twigs do not merely differ in their control capacity, but the behaviour of the stomata in ambient air deviates from the norm. The increasingly uncontrolled water losses during the drought period have a negative effect on photosynthetic capacity. The influence of water deficit on stomatal response to other environmental factors (light, CO₂) is shown. Due to deficient control quality of the stomata lower stress tolerance in the face of drought is suggested in ambient air as compared with pure air. By tracing dysfunctions to structural changes in the cell walls of the stomatal apparatus, a mechanism is described explaining forest decline under the combined influence of air pollutants and drought stress.     

Transpiration as a function of soil temperature and soil water stress

An apparatus was developed for the measurement of transpiration rates of Trifolium repens. The transpiration rates were measured under controlled conditions of soil water stress and soil temperature. Other environmental parameters such as air temperature, relative humidity, light intensity and air speed were held constant. Diffusive resistances were calculated and stomatal aperture changes were recorded for all treatment combinations. A significant interaction between soil water stress and soil temperature was observed for stomatal closures. Stomatal closure was observed even in the so-called wet range of soil water stress. An increase in mesophyll resistance or incipient drying was observed for several treatment combinations. The mesophyll resistance was shown to increase as soil water stress increased.     

Experimental Studies of the Factors Controlling Transpiration: III. THE INTERRELATIONS BETWEEN TRANSPIRATION RATE, STOMATAL MOVEMENT, AND LEAF-WATER CONTENT

Transpiration rates of single leaves of Pelargonium and wheatwere measured under constant conditions of light, temperature,and air flow. Concurrently, stomatal movement was followed withthe resistance porometer during cycles of changing water contentof the leaf and changes induced by light and darkness. Stomatalmovement was found to exert a large controlling influence onthe transpiration rate, whereas water content had an extremelysmall or negligible effect. An approximately inverse linearrelation between transpiration rate and logarithm of resistanceto viscous flow through the leaf is believed to be the resultantof an inverse curvilinear relationship between the diffusiveconductance of the stomata and log. leaf resistance and thedecreasing difference of vapour pressure arising from the highertranspiration rates with increasing stomatal conductances. Nevertheless,the relation demonstrates that the transpiration rate is influencedby the degree of stomatal opening throughout its entire range. There was some evidence of lower transpiration rates duringand after recovery from wilting than before wilting. This isattributed to a decrease in a cell-wall conductance, the evaporatingsurface being located within the cell wall. During wilting partiallyirreversible contraction of the cell wall occurs. There wasalso evidence of slow changes in cell volume at full turgidityattributable to plastic flow. These occurred when the leaf wastransferred from environments of a high to low potential forevaporation. Extensive movement of the stomata followed changes in leaf water,passive opening resulting from decrease and closure from increaseof leaf water. It is suggested that the direction and extentof stomatal changes induced by water deficits is a consequenceof the rate of change of leaf water content and not of the absolutevalues. The stomata also showed an enhanced tendency to closein dry moving air following a period of wilting even after theleaf had regained turgidity.     

Effect of water deficit and sulphur dioxide on total soluble proteins,nitrate reductase activity and free proline content in sunflower leaves

Sunflower (Helianthus annus L. cv. PSH-7) plants were subjected to different osmotic potentials, using polyethylene glycol-6000 (PEG-6000), after, prior to and during SO₂ fumigation. Total soluble proteins and nitrate reductase activity (NRA) decreased, and free proline content increased with the increasing water stress. These biochemical parameters were more adversely affected in fumigated plants than in non-fumigated ones, when mild water stress was provided prior to and during fumigation. When severe water stress was given prior to and during fumigation, total soluble proteins, NRA and free proline content were nearly the same in fumigated and non-fumigated water-stressed plants; it is because the stomatal closure was observed in water-stressed plants. The leaf water potential decreased with the increasing water stress; however, it was not significantly affected due to SO₂ fumigation.     

Sap flow, gas exchange, and hydraulic conductance of young apricot trees growing under a shading net and different water supplies

The experiment was carried out in a research field near Murcia, Spain, over a 3-week period between September 26 and October 16, 2000. Sixteen trees were used in the experiment, eight of which were placed under a rectangular shading net, while the other eight were maintained in the open air. Trees were irrigated once per day and, after October 5th, water was witheld from eight trees (four shaded and four unprotected for 5 days). The leaf stomatal conductance and the photosynthesis rates were higher in the shaded trees than in the exposed plants, probably because the leaf water potential was lower in the unshaded plants. This higher leaf conductance partially compensated for the effect of low radiation on transpiration, and the reduction of daily sap flow registered in shaded trees was only around 10-20%. The net also affected trunk diameter changes, with the shaded trees showing lower values of maximum daily shrinkage. Soil water deficit and high radiation had a similar effect on plant water parameters, lowering leaf water potential, leaf stomatal conductance, and the photosynthesis rate. The effects of both conditions were accumulative and so the exposed water-stressed plants showed the lowest values of total hydraulic resistance and water use efficiency, while the shaded well-irrigated trees registered the highest values for both parameters. For this reason, we think that net shading could be extended to apricot culture in many areas in which irrigation water is scarce and insolation is high.     

Evidence that branch cuvettes are reasonable surrogates for estimating O3 effects in entire tree crowns

Within the scope of quantifying ozone (O(3)) effects on forest tree crowns it is still an open question whether cuvette branches of adult trees are reasonable surrogates for O(3) responses of entire tree crowns and whether twigs exhibit autonomy in defense metabolism in addition to carbon autonomy. Therefore, cuvette-enclosed branches of mature beech (Fagus sylvatica) trees were compared with branches exposed to the same and different ozone regimes by a free-air fumigation system under natural stand conditions by means of a VICE VERSA experiment. For this purpose, cuvettes receiving 1 x O(3) air were mounted in trees exposed to 2 x O(3) and cuvettes receiving 2 x O(3) air were mounted in trees exposed to 1 x O (3) in the upper sun crown. At the end of the fumigation period in September 2004, leaves were examined for differences in gas exchange parameters, pigments, antioxidants, carbohydrates, and stable isotope ratios. No significant differences in foliar gas exchange, total carbohydrates, stable isotope ratios, pigment, and antioxidant contents were found as a consequence of cuvette enclosure (cuvette versus free-air branches) of the same O(3) concentrations besides increase of glucose inside the cuvettes and reduction of the de-epoxidation state of the xanthophyll cycle pigments. No significant ozone effect was found for the investigated gas exchange and most biochemical parameters. The total and oxidized glutathione level of the leaves was increased by the 2 x O(3) treatment in the cuvette and the free-air branches, but this effect was significant only for the free-air branches. From these results we conclude that cuvette branches are useful surrogates for examining the response of entire tree crowns to elevated O(3) and that the defence metabolism of twigs seems to be at least partially autonomous.     

Delignification of subsidiary and guard cell walls of Picea abies (L.) Karst. by fumigation with ozone

Summary After fumigation with ozone, the exterior periclinal walls of the stomatal apparatus of Picea abies appear to be partially delignified, as in earlier experiments with SO₂. This shows up cytophotometrically as reduced UV absorption. Random samples from the stand named Wank in the Bavarian Alps clearly showed a relation between the degree of lignification of the stomatal cells and the grading of the respective trees in their damage classes. The significance of delignification for the regulatory capacity of the stomata is discussed, and a hypothesis is proposed for a specific disturbance of hydroregulation by ozone.     

浑善达克沙地不同植物功能型光合作用和水分利用特征的比较

为了比较不同植物功能型在沙地生境下光合作用和水分利用效率的差异,测定了浑善达克沙地3种功能型的代表种的气体交换特征来比较它们的光合碳固定能力和水分利用状况。3个代表种的气体交换日变化结果表明乔木的光合速率和水分利用效率比草本和灌木的低,而蒸腾速率和气孔导度较高,经过中午的光合午休后,乔木的光合速率在下午没有恢复,而草本和灌木都有不同程度的恢复。在所测定的所有代表物种中,研究地全部的乔木(3种)和灌木(6种)以及典型的草本(2 5种) ,气孔导度与光合速率和蒸腾速率都成显著的正相关关系;另外,在同样的叶片水势情况下,乔木植物的气孔导度最低,在同样的蒸腾速率情况下,乔木植物的光合速率最低。这些结果表明乔木在CO2 同化和H2 O蒸腾平衡上具有低的水分利用效率。从这个角度考虑,我们认为在对沙地进行恢复时,一些草本和灌木种比乔木更合适     

The influence of a fall fumigation with ozone on the stomatal behavior of spruce and fir

Summary Clonal stock (grafts of 15-, 50-, and 100-year-old trees) of spruce (Picea abies (L.) Karst.) and fir (Abies alba Mill.) was exposed either to 150 ppb ozone (300 gm^-3) during 9 daylight hours or to carbon-filtered air on 35 days between 29 August and 21 October 1983. At the end of the fumigation the trees did not exhibit any visible signs of injury. Transpiration and leaf conductance in light and darkness, measured with a Licor porometer, revealed, however, stomatal sluggishness and — in spruce-increased transpiration.     

不同水分条件下盆栽苹果树蒸腾速率动态模拟

土壤水分是制约作物产量和品质的主要环境因素之一,估算不同水分条件下的蒸腾速率（r3对于作物的优质高产和节水灌溉等具有十分重要的意义。通过构建蒸腾．气孔．光合耦合模型可模拟出不同水分条件下苹果树的蒸腾动态,模型参数根据逐步干旱条件下盆栽‘富士’苹果树试验获取。结果表明,Tr主要由饱合水气压差和气孔导度（G。）驱动,同时气象因子和土壤水势对其有强烈的交互作用影响。Tr随土壤水势的下降而减小,当土壤水势低于-0．4MPa时减小幅度更加显著。晴天时,G。在一天中呈双峰曲线,而一呈单峰曲线,最大值出现在13：00左右,约为3．6mmol·m-Ls。根据该模型可计算出不同水分条件下1株盆栽苹果树（总叶片积为O．26m-2）全天的蒸腾总量,供水充足时为652．1g,严重干旱时（土壤水势为-1．5MPa）为85．4g。实测值和模拟值的比较表明,该耦合模型能够模拟出不同土壤水分条件下盆栽苹果树的蒸腾动态以及土壤的含水量。     

Does transpiration control stomatal responses to water vapour pressure deficit?

Three types of observations were used to test the hypothesis that the response of stomatal conductance to a change in vapour pressure deficit is controlled by whole-leaf transpiration rate or by feedback from leaf water potential. Varying the leaf water potential of a measured leaf by controlling the transpiration rate of other leaves on the plant did not affect the response of stomatal conductance to vapour pressure deficit in Glycine max. In three species, stomatal sensitivity to vapour pressure deficit was eliminated when measurements were made at near-zero carbon dioxide concentrations, despite the much higher transpiration rates of leaves at low carbon dioxide. In Abutilon theophrasti, increasing vapour pressure deficit sometimes resulted in both decreased stomatal conductance and a lower transpiration rate even though the response of assimilation rate to the calculated substomatal carbon dioxide concentration indicated that there was no ‘patchy’ stomatal closure at high vapour pressure deficit in this case. These results are not consistent with stomatal closure at high vapour pressure deficit caused by increased whole-leaf transpiration rate or by lower leaf water potential. The lack of response of conductance to vapour pressure deficit in carbon dioxide-free air suggests that abscisic acid may mediate the response.     

Effect of acidic fog on needle surface and water relations of Picea abies

Young spruce trees [ Picea abies (L.) Karst.) exposed to acidic fog (pH 3) showed a disintegration of the epicuticular waxes of the current year's needles as compared with trees treated with a fog of pH 5. The fog treatment was followed by a period in which the trees received different water supply. Under water stress conditions, trees that had been exposed to the acidic fog showed significantly higher transpiration rates than control trees that were treated with a fog of pH 5. The water loss of the controls was 0 at the middle of the photoperiod, while the trees pretreated with acidic fog still showed a substantial transpiration rate at this time. Water loss of excised twigs measured in the dry atmosphere of a desiccator also provided evidence that the water holding capacity of needles pretreated with acidic fog was affected. There is evidence that particularly the cuticular transpiration was increased by pretreatment with acidic fog. The xylem water potential of twigs pretreated with acidic fog was significantly lower than that of twigs pretreated with a fog of pH 5, while the osmotic potential was not affected by the different fog treatments. It is suggested that in draught years trees with a damaged cuticle caused by acidic fog will be affected in their resistance against water stress. In this way acidic fog could be involved in forest decline now widely spread in Central Europe.