Needle Water Potential Research Articles

Short-term changes in free radical scavengers and chloroplast pigments in Pinus canariensis needles as affected by mild drought stress

Summary Potted Pinus canariensis seedlings were subjected to mild drought by withholding irrigation for one week. This treatment induced a reduction in maximum stomatal conductance (50 mmol m −2 s −1 ) compared to irrigated controls (130 mmol m −2 s −1 ). Needle water potentials of non-irrigated trees were maintained at control level (-0.44 MPa). Such a mild drought is a potential oxidative stressor due to the production of active oxygen species (AOS) in illuminated chloroplasts which lack CO 2 due to stomatal closure. Photoprotective pigments (e.g. the xanthophyll cycle) may avoid this situation through light energy dissipation, and antioxidants such as ascorbic acid, tocopherols, and glutathione, may detoxify AOS. Concentrations of ascorbate, glutathione, chlorophyll, and the xanthophyll cycle carotenoids were minimal in the evening (under low light) compared to light-saturated conditions. α-Carotene was highest in the evening. These short-term changes were not affected by drought. The xanthophyll cycle pool tended to be more de-epoxidized in strongly illuminated needles of non-irrigated trees at the beginning of the experiment, but this effect was transient. The glutathione pool was more oxidized in needles of non-irrigated trees (up to 20 percnt; of total vs. 10 percnt; at control) after the xanthophyll changes took place, whereas the redox state of ascorbate remained stable.

Effects of water supply on gas exchange in Pinus pinaster Ait. provenances during their first growing season

Gas exchange parameters were monitored during the first growing season on Pinus pinaster young seedlings belonging to six provenances and submitted to two water supply regimes in the open air under cover. Significant differences were found between water supply regimes and measurement dates; sometimes also between provenances. Gas exchange rate responses to needle water potential were similar for all the provenances, and rate changes were only detected as water potential went down to less than $-1.3$ MPa. The Iberian provenances, in contrast to the Landes, showed a tendency to save water at the end of Spring, which indicates an adaptation to locations with Summer drought. The growth differences between provenances were not expressed in terms of differences in the instantaneous net photosynthetic rate, since this will depend on other factors, such as seedling water status and the time that the measurement was made. However, provenance growth differences may be partially explained by the differences in water use efficiency and nitrogen productivity.

Diurnal changes in water conduction in loblolly pine (Pinus taeda) and Virginia pine (P. virginiana) during soil dehydration.

We studied diurnal changes in water conduction during soil dehydration in 37-month-old seedlings of one Virginia pine (Pinus virginiana Mill.) and two loblolly pine (P. taeda L.) sources, one from North Carolina (NC) and the other from the "Lost Pines" areas of Texas (TX), in an environmentally controlled growth chamber. For seedlings of similar biomass, the TX source had higher values of transpiration, needle conductance, and plant hydraulic conductivity under well-watered conditions than the NC source. Under dry soil conditions, the TX source had lower values of water conduction than the NC source. The Virginia pine source responded similarly to the TX source under both well-watered and dry soil conditions. For all three pine sources, gradients between soil and needle water potentials were greatest when the seedlings were moderately stressed. The TX and Virginia pine sources had higher gradients and lower daytime needle water potentials under moderate stress conditions than the NC source. Predawn needle water potentials did not differ among the pine sources. We conclude that the TX and Virginia pine sources have decreased daytime needle water potentials and increased water potential gradients during the daytime under moderate stress conditions, but with no disruption of recovery at predawn. The greater rates of transpiration and water conduction by the TX source compared with the NC source under well-watered conditions suggest a means by which growth can be maximized prior to the onset of drought, thereby enhancing survival of loblolly pines in drought-prone environments.

Effects of drought stress and severe pruning on the reaction zone induced by single inoculations with a bark beetle associated fungus (Ophiostoma ips) in the phloem of young Scots pines

The objective of this study was to test the effect of water stress and pruning on the resistance of young Scots pines (Pinus sylvestris L.) to a bark beetle associated fungus. Six-year-old potted trees were either pruned (70% of needles removed) or subjected to several successive episodes of severe water stress, prior to inoculation of inner bark with the fungus Ophiostoma ips (Rumb.) Nannf., which is usually associated with the bark beetle Ips sexdentatus Boern. Well-watered, nonpruned trees served as controls. Predawn needle water potential reached -2.5 MPa and net CO2 assimilation rates were reduced to almost zero during each water stress episode. The length of the reaction zones around inoculation points reached 3-4 cm after 3 weeks. It was higher during Spring than during Autumn. Impact of water stress on the length of the reaction zone was very limited and independent of the number of drought episodes that had been imposed prior to inoculation. The only visible change was a slight decrease when the inoculation was done during the period of maximum water stress intensity. Growth of the pathogen in the phloem was not affected by water stress. Correspondingly, pruning had no effect on either of these two parameters. Induced reaction zones accumulated monophenolic compounds that were undetectable in unwounded phloem. These included pinocembrin and pinosylvin and its monomethylether known to contribute to the defence against the fungus. Neither drought nor severe pruning induced any change in the nature or concentrations of these compounds in the unwounded phloem or in the reaction zone.

Relationships between nitrogen uptake, leaf area, water status and growth in an 11-year-old Pinus radiata plantation in response to thinning, thinning residue, and nitrogen fertiliser

Abstract Nitrogen and water status were manipulated experimentally by thinning, residue management and application of N and P fertiliser. The experiment was thinned in November 1988, residue treatments were installed in December 1988 and fertiliser was applied in September 1989. Basal area increment (m 2 ha −1 ) increased in response to thinning, the quantity of residue retained, and with the rate of N fertiliser. There was no response to P nor any N×P interaction. Nitrogen uptake in 1989–1990 was highly correlated with tree growth in thinned treatments over the next 3 years. The positive growth response to N uptake was mediated primarily through increased leaf area index (LAI). Thus LAI in 1991 was highly correlated with N uptake in 1989–1990 and with subsequent growth. Growth per unit N uptake or per unit leaf area were much lower in the unthinned treatment where predawn needle water potentials ( Ψ ) were consistently more negative than the thinned treatments. Combining Ψ with N uptake or LAI in a simple linear model explained 96% and 94%, respectively of the variation in tree growth for all treatments. Annual growth increments in thinned treatments not fertilised with N were correlated with current N uptake. In N fertilised treatments, growth was highly correlated with N uptake in the year after fertiliser application but was then independent of subsequent N uptake. Foliar N concentrations in June 1990 were highly correlated with N uptake and subsequent growth in thinned treatments. However, treatment concentration differences declined with time while differences in growth remained due to differences in LAI. Consequently, the correlation between foliar N concentration and growth was substantially reduced. An index of canopy N content (LAI×foliar N concentration) was no better correlated with growth than LAI alone. Litter N concentrations (maxima, minima or mean annual weighted) in thinned treatments were correlated with tree growth in the subsequent year. Regression coefficients were initially low but increased up to a maximum of 0.90 for growth in 1990–1993. Stem growth in both thinned and unthinned treatments could be explained by combining foliar or litter N concentrations with Ψ in a simple linear relationship. Litter N concentrations could not be used to estimate N uptake.

The response of Pinus sylvestris to drought: stomatal control of transpiration and hydraulic conductance.

We investigated the impact of drought on the physiology of 41-year-old Scots pine (Pinus sylvestris L.) in central Scotland. Measurements were made of the seasonal course of transpiration, canopy stomatal conductance, needle water potential, xylem water content, soil-to-needle hydraulic resistance, and growth. Comparison was made between drought-treated plots and those receiving average precipitation. In response to drought, transpiration rate declined once volumetric water content (VWC) over the top 20 cm of soil reached a threshold value of 12%. Thereafter, transpiration was a near linear function of soil water content. As the soil water deficit developed, the hydraulic resistance between soil and needles increased by a factor of three as predawn needle water potential declined from -0.54 to -0.71 MPa. A small but significant increase in xylem embolism was detected in 1-year-old shoots. Stomatal control of transpiration prevented needle water potential from declining below -1.5 MPa. Basal area, and shoot and needle growth were significantly reduced in the drought treatment. In the year following the drought, canopy stomatal conductance and soil-to-needle hydraulic resistance recovered. Current-year needle extension recovered, but a significant reduction in basal area increment was evident one year after the drought. The results suggest that, in response to soil water deficit, mature Scots pine closes its stomata sufficiently to prevent the development of substantial xylem embolism. Reduced growth in the year after a severe soil water deficit is most likely to be the result of reduced assimilation in the year of the drought, rather than to any residual embolism carried over from one year to the next.

Water balance of Pinus halepensis Mill. afforestation in an arid region

Transpiration ( T ), needle water stress (MPa) and the water balance of an Aleppo pine ( Pinus halepensis Mill.) plantation, growing in an arid region at the edge of the Israeli Negev desert, were studied during 1 yr. The heat pulse technique for the measurement of the heat flow velocity was used for the estimation of the sap flow velocity, i.e., transpiration, in the stems of 16 trees (27% of the trees in a plot of 1000 m 2 ). A pressure chamber was used to determine the needle water potential (MPa). Climatic parameters were measured in the forest for the computation of the potential transpiration ( T p ) by means of the Penman–Montheith equation. During the rainy period, the transpiration ( T ) rate was maintained at a level between 1 and 2 mm day −1 , which then dropped after the last rain; the decrease of T in small trees (diameter at breast height [DBH]<12 cm) was much faster than that in larger trees (DBH>12 cm). In May, T dropped to a nondetectable rate (about 0.02 mm day −1 ) and remained at this level till the next significant rain in December. A maximum T / T p ratio of 0.3, which is nearly half of the ratio found previously in an Aleppo pine plantation under Mediterranean climatic conditions (Schiller and Cohen, 1995), was recorded in February. This difference between the two sites, in T / T p ratio, is attributed to the difference in the basal area of the trees between the two sites. Needle water potential at sunrise decreased from −0.8 MPa in the rainy period to more than −3.0 MPa during the dry period. The integrated T throughout the measurement period was used to estimate the total water uptake by the stand, which was 210.1 mm, i.e., 93% of the effective rainfall, or 80.2% of the total annual rainfall.

Combined effects of acid mist and frost on the water status of young spruce trees ( Picea abies)

Acid mist (pH 3) precipitation led to a degradation of the epicuticular waxes of the youngest needles. Under the influence of frost drought in spring those affected trees resulted in a detrimental decline in needle water potential and turgor potential. The results indicate that a damaged, poor cuticle loweres the water retention capability and increases water losses by non stomatal, cuticular transpiration. Therefore acid mist treated trees seem to be more endangered to water stress under frost drought conditions in spring than trees with an intact cuticula. The results are in agreement with observations of decline symptoms under field conditions after years of drought. The influence of mist acidity in combination with frost simulatio during winter time were of minor importance.

Combined effects of acid mist and frost drought on the water status of young spruce trees ( Picea abies)

Abstract This investigation was focused on the effect of frost drought following acid mist exposure on the water status and CO2 assimilation of young spruce trees (Picea abies). Trees cultivated in special containers were exposed to acid mist with pH 3 and a control mist with pH 5 for 10 weeks with three mist events per week during autumn. Frost drought, indicating frozen soil with atmospheric conditions allowing transpiration, was simulated in spring for 6 weeks. The controls for frost drought treatments were treatments with humid non-frozen soil. Acid mist application resulted in degradation of the epicuticular needle waxes with melted wax threads and larger lesions in the wax layer. Control needles showed a well-developed epicuticular wax layer. Frost drought inhibited transpiration and CO2 uptake in both mist treatments almost completely due to stomatal closure. In contrast, trees showed considerable transpiration and CO2 uptake rates in the treatments with non-frozen soil. Needle water potential of trees (control soil) was normal (−0.60 MPa), whereas water potential in trees of frozen soil was significantly lower, with −1.49 MPa in the control and −2.26 MPa in the acid mist treatment indicating water stress. We suppose from this finding that the deteriorated wax layer impaired the water retention capacity of needles and allowed higher cuticular transpiration compared with the control treatment. Frost drought was associated with a large decrease in starch concentration of needles paralleled by an increase of glucose and fructose concentration, which is suggested to have increased the osmotic potential. This rise in osmotic potential obviously enabled plants of the frost drought treatment+control mist to maintain their turgor which was not different from the turgor of needles from the non-frozen soil treatments. Needles of the frost drought+acid mist treatment, however, had a weak turgor, indicating that in this treatment a strong water stress prevailed. It is suggested that also under natural forest conditions frost drought preceded by acid mist exposure may cause severe forest damage and decline.

Influence of ammonia and ozone on growth and drought sensitivity of Pinus sylvestris

Abstract Four-year-old Pinus sylvestris trees were exposed to ammonia (16, 55, 110 ppb for 24 h d -1 ) and ozone (0, 45 and 68 ppb, 9 h d -1 ) in a factorial design in open-top chambers for 15 months. Treatment effects on tree growth and architecture were assessed during two growing seasons; effects on sensitivity to drought stress were determined during the second growing season. Tree height and stem diameter increments were stimulated by NH 3 . The tree architecture was influenced only by NH 3 giving the trees a stunted appearance. Exposure to NH 3 resulted in lower needle water potentials both in fully watered trees and in droughted trees, indicating an increased susceptibility to drought. When the trees were drought stressed, the water potential in needles exposed to NH 3 alone decreased linearly with the NH 3 concentration. Trees exposed to NH 3 +O 3 maintained a less negative needle-water potential after a drought treatment, indicating an ameliorative effect of O 3 on drought sensitivity although the relative decrease in water potential during the drought treatment was larger than in trees exposed to only NH 3 . Drought-stress phenomena were also enhanced by NH 3 by increasing the amount of needles relative to the root biomass. Although the biomass of fine roots was increased by NH 3 as well as by O 3 , NH 3 increased the needle biomass more, increasing the needle:root ratio and thus drought stress.

Effect of elevated carbon dioxide concentration and root restriction on net photosynthesis, water relations and foliar carbohydrate status of loblolly pine seedlings.

To determine the effects of CO(2)-enriched air and root restriction on photosynthetic capacity, we measured net photosynthetic rates of 1-year-old loblolly pine seedlings grown in 0.6-, 3.8- or 18.9-liter pots in ambient (360 micro mol mol(-1)) or 2x ambient CO(2) (720 micro mol mol(-1)) concentration for 23 weeks. We also measured needle carbohydrate concentration and water relations to determine whether feedback inhibition or water stress was responsible for any decreases in net photosynthesis. Across all treatments, carbon dioxide enrichment increased net photosynthesis by approximately 60 to 70%. Net photosynthetic rates of seedlings in the smallest pots decreased over time with the reduction occurring first in the ambient CO(2) treatment and then in the 2x ambient CO(2) treatment. Needle starch concentrations of seedlings grown in the smallest pots were two to three times greater in the 2x ambient CO(2) treatment than in the ambient CO(2) treatment, but decreased net photosynthesis was not associated with increased starch or sugar concentrations. The reduction in net photosynthesis of seedlings in small pots was correlated with decreased needle water potentials, indicating that seedlings in the small pots had restricted root systems and were unable to supply sufficient water to the shoots. We conclude that the decrease in net photosynthesis of seedlings in small pots was not the result of CO(2) enrichment or an accumulation of carbohydrates causing feedback inhibition, but was caused by water stress.

Continuous measurements of water tensions in the xylem of trees based on the elastic properties of wood

According to the cohesion theory for the ascent of water in vascular plants, significant tensions should develop in the water columns of transpiring trees. These tensions cause small but detectable changes in the diameter of the xylem as a consequence of adhesive forces between water molecules and the inner xylem walls. The diurnal time course of tension in the water columns in the xylem of the trunk of mature Scots pine (Pinus sylvestris L.) was measured during the summer of 1995 by means of a displacement transducer mounted on a rigid steel frame. The apparent elastic modulus of Scots pine wood in the radial direction (E ′ r ) was determined in the laboratory and then used to estimate tensions from the measured displacement. Laboratory measurements on logs indicated that only the sapwood contributed to dimensional changes of the xylem. Corrections for thermal expansion of the system were included. Water tensions fell by 0.19 MPa over the course of the day, when needle water potentials fell by 0.50 MPa. Such data are consistent with the cohesion theory, and with the view that the hydraulic resistances to flow in above- and below-ground plant parts are of similar magnitude.

Sphaeropsis sapineaand Water Stress in a Red Pine Plantation in Central Wisconsin

ABSTRACT A study was conducted to determine the effects of water stress resulting from competing vegetation on disease development of Sphaeropsis sapinea in red pine plantations. A 9-year-old plantation was selected in 1992 and experiments were conducted for three consecutive years. Four treatments were assigned at random to individual trees: no treatment, herbicide to kill surrounding weeds, supplemental water, and both herbicide and supplemental water. Two isolates of each S. sapinea morphotype (A and B) were used to inoculate wounded lateral shoots. Disease development was measured as the maximum distance below the inoculation site at which necrotic needles were observed. Nonwatered trees with competing vegetation (nontreated condition) had significantly lower predawn needle water potentials (more water stress) and more severe disease development than trees that received the herbicide, water, or combined herbicide and water treatments. The most severe disease occurred in the driest year and the least in the wettest year. Competing vegetation indirectly affected disease development by inducing water stress, even in relatively moist years, on trees previously considered well established. Isolates of morphotype A were more aggressive than isolates of morphotype B. Conclusions from this research have implications for sustainable management of the region's conifer forests.

Effects of Moderate Water Stress on Disease Development by Sphaeropsis sapinea on Red Pine

ABSTRACT The aggressiveness of Sphaeropsis sapinea isolates was compared on water-stressed and nonstressed 3-year-old red pines (Pinus resinosa) in greenhouse and growth chamber experiments. Water was withheld from stressed seedlings to achieve mean predawn needle water potentials (psi(PD)) above -1.9 MPa. The lowest mean psi(PD) of well-watered seedlings was maintained at or above -0.8 MPa. Young shoots were inoculated by placing colonized agar plugs on wounds made by removing a needle fascicle. Two isolates of each recognized morphotype (A and B) were used in the greenhouse experiment and two isolates of morphotype A were used in the growth chamber experiment. After 4 weeks, isolates of morphotype A caused more severe symptoms and could be recovered farther from the inoculation site on water-stressed than on nonstressed trees in both experiments. In the greenhouse experiment, isolates of mor-photype A also caused more severe symptoms and could be recovered farther from the inoculation site than isolates of morphotype B, regardless of watering regime. These results indicate that water stress at levels observed typically in the field can result in increased disease development by isolates of S. sapinea morphotype A on red pine. The reduction of water stress of red pines in the field may reduce losses due to Sphaeropsis shoot blight.

Duration of Water Stress Affects Development of Sphaeropsis Canker on Scots Pine

Saplings of Pinus sylvestris were subjected to drought stress periods and inoculated with Sphaempsis sapinea in a greenhouse experiment. Six wk after inoculation, saplings that had low needle water potentials for 14 to 21 days after inoculation exhibited more dieback and developed significantly (P &lt; 0.05) longer cankers than saplings that had equivalent water stress for 3 to 4 days after inoculation or unstressed saplings. The results indicate that drought stress increases susceptibility of Scots pine to Sphaeropsis canker and that canker growth can be suppressed by watering drought-stressed trees.

Fine root electrolyte leakage and moisture content: indices of Sitka spruce and Douglas-fir seedling performance after desiccation

In spring 1992, 2-year-old bare-rooted seedlings of Sitka spruce (Picea sitchensis (Bong.) Carr.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were exposed for 0, 0.5, 1.0, 1.5, or 3 h in a controlled environment room at 20°C. Plants were desiccated in batches during February and March; 100 seedlings of each species were planted in 5 20-plant plots at each of 6 planting sites using the normal planting times and methods of each area. The effect of exposure was assessed within 24 h of desiccation on a subsample of plants by measuring fine root moisture content and electrolyte leakage and, in a limited number of cases, needle water potential. These measures were related to survival and growth after the first and second growing seasons.

Growth and Water Relations of P. tabulaeformis Seedlings Inoculated with Ectomycorrhizal Fungi.

The effects of infection with two ectomycorrhizal fungi, Suillus luteus and Gomphidius viscidus, on the growth and drought-tolerance of Pinus tabulaeformis (Chinese pine) seedlings under water stress conditions were examined. The growth of plants inoculated with the mycorrhizal fungi was consistently greater than that of nonmycorrhizal plants. Six months after inoculation, dry weight of mycorrhizal plants was about 2.1 times greater. Under water stress condition, net photosynthesis rate, needle water potential, and water use efficiency of mycorrhizal plant increased significantly. From these experiments, growth and drought-resistance of P. tabulaeformis were shown to be enhanced significantly by infection with the mycorrhizal fungi. The ability of 3 fungi including Cenococcum graniforme to grow under conditions of low water potential was tested in pure culture. C. graniforme and S. luteus showed negligible growth with water potentials lower than -2.0MPa. However, G. viscidus continued to grow at -2.0MPa. All of the mycorrhizal fungi showed maximum growth at -0.5MPa.

Photosynthetic responses to needle water potentials in Scots pine after a four-year exposure to elevated CO(2) and temperature.

Effects of needle water potential (Psi(l)) on gas exchange of Scots pine (Pinus sylvestris L.) grown for 4 years in open-top chambers with elevated temperature (ET), elevated CO(2) (EC) or a combination of elevated temperature and CO(2) (EC + ET) were examined at a high photon flux density (PPFD), saturated leaf to air water vapor pressure deficit (VPD) and optimal temperature (T). We used the Farquhar model of photosynthesis to estimate the separate effects of Psi(l) and the treatments on maximum carboxylation efficiency (V(c,max)), ribulose-1,5-bisphosphate regeneration capacity (J), rate of respiration in the light (R(d)), intercellular partial pressure of CO(2) (C(i)) and stomatal conductance (G(s)). Depression of CO(2) assimilation rate at low Psi(l) was the result of both stomatal and non-stomatal limitations on photosynthetic processes; however, stomatal limitations dominated during short-term water stress (Psi(l) < -1.2 MPa), whereas non-stomatal limitations dominated during severe water stress. Among the nonstomatal components, the decrease in J contributed more to the decline in photosynthesis than the decrease in V(c,max). Long-term elevation of CO(2) and temperature led to differences in the maximum values of the parameters, the threshold values of Psi(l) and the sensitivity of the parameters to decreasing Psi(l). The CO(2) treatment decreased the maximum values of V(c,max), J and R(d) but significantly increased the sensitivity of V(c,max), J and R(d) to decreasing Psi(l) (P < 0.05). The effects of the ET and EC + ET treatments on V(c,max), J and R(d) were opposite to the effects of the EC treatment on these parameters. The values of G(s), which were measured simultaneously with maximum net rate of assimilation (A(max)), declined in a curvilinear fashion as Psi(l) decreased. Both the EC + ET and ET treatments significantly decreased the sensitivity of G(s) to decreasing Psi(l). We conclude that, in the future, acclimation to increased atmospheric CO(2) and temperature could increase the tolerance of Scots pine to water stress.

Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree

ABSTRACTSudden but transient changes in the fraction or illuminated foliage area in a well‐watered 7‐year‐old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (gt), stomatal conductance (gs) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in gt. However, when tree conductance was normalized with respect to the illuminated leaf area (gt'), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in gs and A up to 59 and 24%, respectively, for needles in the top third of (he crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.

Response of giant sequoia canopy foliage to elevated concentrations of atmospheric ozone.

We examined the physiological response of foliage in the upper third of the canopy of 125-year-old giant sequoia (Sequoiadendron giganteum Buchholz.) trees to a 61-day exposure to 0.25x, 1x, 2x or 3x ambient ozone concentration. Four branch exposure chambers, one per ozone treatment, were installed on 1-m long secondary branches of each tree at a height of 34 m. No visible symptoms of foliar ozone damage were apparent throughout the 61-day exposure period and none of the ozone treatments affected branch growth. Despite the similarity in ozone concentrations in the branch chambers within a treatment, the trees exhibited different physiological responses to increasing ozone uptake. Differences in diurnal and seasonal patterns of g(s) among the trees led to a 2-fold greater ozone uptake in tree No. 2 compared with trees Nos. 1 and 3. Tree No. 3 had significantly higher CER and g(s) at 0.25x ambient ozone than trees Nos. 1 and 2, and g(s) and CER of tree No. 3 declined with increasing ozone uptake. The y-intercept of the regression for dark respiration versus ozone uptake was significantly lower for tree No. 2 than for trees Nos. 1 and 3. In the 0.25x and 1x ozone treatments, the chlorophyll concentration of current-year foliage of trees Nos. 1 and 2 was significantly higher than that of current-year foliage of tree No. 3. Chlorophyll concentration of current-year foliage on tree No. 1 did not decline with increasing ozone uptake. In all trees, total needle water potential decreased with increasing ozone uptake, but turgor was constant. Although tree No. 2 had the greatest ozone uptake, g(s) was highest and foliar chlorophyll concentration was lowest in tree No. 3 in the 0.25x and 1x ambient atmospheric ozone treatments.