Red Spruce Seedlings Research Articles

Spruce–fir decline and gap dynamics on Camels Hump, Vermont

Widespread and conspicuous dieback of red spruce (Picearubens Sarg.) accompanied by asymptomatic declines in balsam fir (Abiesbalsamea (L.) Mill.) and white birch (Betulapapyrifera var. cordifolia (Regel.) Fern.) trees on Camels Hump, Vermont, prompted an investigation into the role of spruce–fir decline on gap expansion, tree health, and regeneration dynamics. Forty percent of the study area on Camels Hump was occupied by recent forest gaps in the summer of 1989. Gaps were growing northwesterly (direction 322°) at a rate of 0.8–1.2 m•year−1. Prevailing winds in the study area are from the south-southeast. Gap expansion appears to play a dominant role in continuing forest disturbance. Red spruce vigor was low in all dominance classes (53% foliar retention), while vigor of balsam fir and birch (yellow (Betulaalleghaniensis Britt.) and white) was somewhat higher. Exposure and wind flagging of different tree species within the same crown dominance classes were similar, but apical foliar damage was greater in spruce than in fir or birch. Red spruce and birch trees were older than balsam fir within comparable crown classes. Wind flagging was significantly correlated with crown exposure in red spruce and balsam fir, while diameter was the most important factor related to flagging in birch. All three species tended to die while standing. Dead balsam fir trees were twice as likely as red spruce to have been windthrown or diseased, whereas dead red spruce showed a much higher incidence of past and present insect infestation. Live birch had low levels of biotic damage. Density of red spruce seedlings was low within gaps and adjacent canopy sites. Balsam fir seedling density was significantly higher in the canopied areas, whereas birch density was marginally higher in gap areas. There were no significant differences in ages of spruce or fir seedlings growing in gaps and closed canopy areas. Birch seedlings in gaps were older and taller than those under the canopy, indicating low survivorship of birch under the forest canopy. It is likely that this forest will be predominantly composed of balsam fir and birch in the near future.

Growth and water relationships of red spruce seedlings exposed to atmospheric deposition and drought

Two-year-old containerized seedlings of red spruce (Picearubens Sarg.) were subjected to ozone (O3) fumigation (0.25 ppm), simulated acid rain (pH 4.2 or 3.0), and drought prior to measurement of changes in growth and plant water status. Drought caused a significant decline in terminal height growth and new-shoot dry weight, but old-shoot dry weight, root dry weight, and root/shoot ratio were not appreciably affected. Deposition treatment (O3 and (or) acid rain) influenced both shoot and root dry weight but did not significantly affect height or root/shoot ratio. Treatment with either 0.25 ppm O3 alone or pH 3.0 rainfall alone caused the greatest reduction in growth, while treatment with 0.25 ppm O3 + pH 4.2 rain had the least effect. The influence of deposition treatment generally was more pronounced in seedlings subjected to drought than in well-watered plants. Seedlings subjected to drought had lower (more negative) water potentials than well-watered plants regardless of deposition treatment. While there were no significant differences in the water status of well-watered seedlings exposed to various deposition treatments, xylem water potential and osmotic potential of drought-stressed seedlings treated with O3 alone were consistently lower than these characteristics in seedlings treated with O3 + acid rain together. Except for one deposition treatment (0.25 ppm O3 + pH 3.0 rain) there was no evidence for osmotic adjustment of red spruce seedlings in response to stress factors imposed in this study.

The effect of long‐term ozone exposure on injury in seedlings of red spruce (Picea rubens Sarg.)

summaryThe death of many mature red spruce (Picea rubens Sarg.) trees in the northeastern United States has sparked controversy over the roles natural factors and air pollutants play. The goal of this work was to investigate the effects of long‐term ozone exposures on development of injury and, in particular, the expression of winter injury in red spruce. Red spruce seedlings were exposed to elevated levels of ozone during two growing seasons, starting just after budbreak, and continuing into the period of early frosts. Trees spent both winter periods under ambient conditions of light and temperature. No visible lesions on foliage that could be attributed to ozone developed during the growing seasons. Yellow and brown needles appeared each winter, with much more injury in the second year. However, in the spring after two seasons of ozone exposure, there was no significant effect of ozone on the overall appearance of the entire population of seedlings. Samples were taken for histology and ultrastructure approximately monthly. Ozone treatments increased mesophyll cell disruption after frosts in early winter in the first year, but not in the second. There was no correlation between histological injury in the autumn and visible symptoms in the spring, indicating that there may be different aspects of the winter injury syndrome. In the second summer from 20 to 40%, of all mesophyll cells were damaged. This damage was not related to ozone treatment, and probably resulted from high summer temperatures.

Soil Chemistry and Nutrition of North American Spruce‐Fir Stands: Evidence for Recent Change

AbstractOne set of hypotheses offered to explain the decline of red spruce (Picea rubens Sarg.) in eastern North America focuses on the effect of acidic deposition on soil chemistry changes that may affect nutrient availability and root function. Long‐term soils data suggest that soil acidification has occurred in some spruce stands over the past 50 yr, with plant uptake and cation leaching both contributing to the loss of cations. Studies of tree ring chemistry also have indicated changes in Ca/Al and Mg/Al ratios in red spruce wood, suggesting increases in the ionic strength of soil solution. Irrigation studies using strong acid inputs have demonstrated accelerated displacement of base cations from upper horizons. Spruce‐fir (Abies spp.) nutrient budgets indicate that current net Ca and Mg leaching loss rates are of the same order of magnitude as losses to whole tree harvest removals, spread out over a 50‐yr rotation. For most cations, red spruce foliar nutrient levels decline with elevation, but it is difficult to assess the contribution of the elevational gradient in atmospheric deposition to this pattern. Compared to northeastern sites, spruce‐fir soil solutions in the southern Appalachians have higher nitrate levels and higher Al concentrations, which at times approach the Al toxicity threshold for red spruce seedlings and frequently are at levels known to interfere with cation uptake. There is little evidence that either nutrient deficiencies or Al toxicity are primary causes of red spruce decline in the Northeast, though both may play a role in the Southeast. Major factors that could affect soil chemistry in spruce‐fir stands in the future are (i) changes in S and N deposition, (ii) climate changes affecting soil organic matter decomposition and nutrient uptake, and (iii) tree mortality and physical disturbances to soils resulting in soil nitrate release.

Responses of red spruce seedlings to ozone and acid deposition

Red spruce (Picearubens Sarg.) seedlings were treated with ozone and simulated acid precipitation to determine the effects of these pollutants on growth, nonstructural carbohydrates, and foliar mineral content. One-year-old seedlings were fumigated with ozone (at 0.15 μL/L for 6 h/d or at 0.15 μL/L for 6 h/d plus 0.07 μL/L for 18 h/d) and treated with simulated precipitation (pH 3.5, 4.0, or 4.5) for up to 28 weeks. Seedlings were harvested at 7-week intervals. Ozone had no effect on growth, and precipitation acidity affected only terminal length. Carbohydrate pools were altered little by the ozone and precipitation treatments. Of eight minerals tested, only Ca was affected by precipitation acidity and only P and Cu were affected by ozone. The results of this experiment show that red spruce seedlings that receive ample supplies of water and nutrients are tolerant to ozone and changes in precipitation acidity.

Ambient cloud deposition reduces cold tolerance of red spruce seedlings

Laboratory cold-tolerance assessments were conducted between September 1989 and March 1990 on red spruce (Picearubens Sarg.) seedlings exposed to combinations of ozone (O3) and cloud water for two growing seasons on the summit of Whitetop Mountain, Virginia. Chamber treatments consisted of exposure to (i) ambient O3 and cloud water, (ii) ambient O3 and no cloud water, or (iii) reduced O3 and no cloud water. Ambient-air field plots were included to assess possible chamber effects. Red spruce seedlings exposed to ambient O3 and cloud water, either in chambers or field plots, were generally least cold tolerant, and differences were significant in October, November, December, and January. During 3 of those months, seedlings exposed to ambient O3 and cloud water in chambers were significantly less cold tolerant than either seedlings exposed to reduced O3 and no cloud water or seedlings exposed to ambient O3 only. There were no definitive effects of O3 in any month. The reduction in cold tolerance of seedlings exposed to O3 and cloud water appeared to result from the negative influences of acidic cloud deposition, rather than O3. This is the first conclusive evidence that ambient cloud deposition can impair the development of cold tolerance and maximum cold tolerance achieved in midwinter for red spruce growing in its native habitat. The 3 to 5 °C reduction in cold tolerance associated with exposure to ambient cloud water in this study may be sufficient to explain the winter injury observed frequently in northern montane red spruce stands over the past 4 decades.

Sulphate and ammonium in mist impair the frost hardening of red spruce seedlings

summaryTwo‐year‐old seedlings of red spruce [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were grown in open‐top chambers supplied with charcoal‐filtered air near Edinburgh, Scotland. Between May and November 1988, plants were exposed to mists containing NH4+, SO42− and NO3− ions at concentrations of 1.6 mol m−3 and H+ at 3.2 mol m−3, in pairwise combination and all together. The mists were applied twice weekly at a rate of 2 mm precipitation equivalent per application. Treatment with H2SO4 severely damaged the plants after 3 wk; the concentration for this treatment was therefore reduced from 1.6 mol m−3 to 0.5 mol m3, and new plants were substituted, in June 1988. Frost hardiness was assessed by freeze‐testing detached shoots, then measuring rates of electrolyte leakage. No effects of the mist treatments were detected during the early stages of frost hardening, but on 31 October, shoots that had received sulphate and ammonium ions were less hardy than ‘control’ shoots treated with deionized water. The temperature which killed 20% of shoots was 14 °C higher, and the temperature which killed 56% of shoots was 7 °C higher than for ‘control’ shoots. Acidity per se had no effect on frost hardiness; nitrate ions had no effect and may have mitigated the effects of sulphate when applied together.The results confirm earlier data, and indicate that uptake of NH4+ and SO42− ions can disturb the frost‐hardening process. There are important implications for pollution control strategies in the northeastern United States, if damaging interactions between frost hardiness of red spruce and pollutant deposition are linked to ammonium and sulphate rather than nitrate ions.

Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by exposure to ozone for two growing seasons

summaryThree‐year‐old red spruce seedlings were exposed to various concentrations of ozone, from 0.4 to 3 times ambient, for two consecutive growing seasons in open‐top chambers in Ithaca, NY, USA. Exposures, which varied with changes in daylength, were from 30 May to 14 December 1987 and 1 June to 1 December 1988. Seedling biomass, foliar pigments and carbohydrate content of roots and shoots were assessed once or twice per month. Tree biomass increased through the summer and declined slightly in late autumn, regardless of ozone treatment. Biomass and contents of sugar and starch of 1988 fixed growth declined linearly with exposure to increasing levels of ozone. Rates of decline in total shoot biomass and old shoot biomass increased linearly with exposure to increasing concentrations of ozone, but tree height was not affected. Seasonal means of starch content of roots decreased linearly with increasing doses of ozone, but in contrast seasonal mean sugar content and rate of sugar accumulation of roots increased linearly. Chlorophyll a and chlorophyll b contents were not affected by ozone.These data are consistent with the concept that ozone stress is cumulative, since effects on biomass and carbohydrate content of roots and shoots were not detected after the first year of exposure, but were detected after the second year of treatments. Furthermore, biomass was reduced by ozone only in tissues that were initiated during the first year of exposures and developed during the second year of exposures (1988 fixed growth).

A laboratory investigation of the routes of HNO 3 dry deposition to coniferous seedlings

White pine, Norway spruce and red spruce seedlings were exposed to nitric acid vapor concentrations of 10 to 120 ppb in constant stirred tank reactors. Nitric acid dry deposition rates were determined from both the change in nitric acid concentration in the reactor flow stream and from the amount of nitrogen recovered from the seedlings. Nitric acid labeled with 15N was used to distinguish dry-deposited nitrogen in the plant from the nitrogen that was already present. It was found that dry deposition occurs via three routes: surface deposition, trans-cuticular deposition, and stomatal deposition. Resistance to surface deposition is very low (< 4·8 m 2-s mol −1) for a freshly washed surface, but increases as the surface adsorption sites are occupied. Resistance to trans-cuticular uptake averaged 206 m 2-s mol −1. Stomatal resistance can be calculated from the rate of water diffusion out of the plant. Eighty per cent of the nitric acid deposited via the trans-cuticular and stomatal routes was assimilated by the plant. However, none of the nitric acid deposited on the surface was assimilated. In rural areas with coniferous forests, the combination of low ambient nitric acid concentrations and low initial surface resistance means that most nitric acid will be dry deposited on the tree surface, and thus will not be directly assimilated.

Red spruce seedling health: an assessment of acid fog deposition and heavy metal soil contamination as interactive stress factors

Two-year-old spruce (Picearubens Sarg.) seedlings were exposed to 12 treatment regimes of acid fog deposition and heavy metal soil amendment over a 2-year period. Seedling health was assessed by measuring five health indices, including general vigor estimate, height, diameter, bud number, and biomass (leaf, stem, and twig, and total). Soil was amended with cadmium, copper, lead, manganese, nickel, and zinc added in amounts comparable to high-elevation forest soils in the northeastern United States. Seedlings were also treated with simulated fog, with ionic chemistry similar to high-elevation northeastern fog events, adjusted to pH 3 or 5. The seedlings were planted in metal-amended soil and subjected to fog treatments in greenhouse chambers from August 6, 1986, to October 29, 1987, in weekly regimes of 30-h exposures. Of all the seedling stress factors imposed, only the lead amendment at 2000 ppm concentration, which is approximately 10 times the current ambient forest floor high-elevation level, had a consistently adverse impact on the seedling health parameters measured. Vigor rating of experimental seedlings was adversely impacted by precipitaton acidity in the absence of lead and other heavy metal soil amendments. Height, diameter, and live bud count of the seedlings were quite insensitive to treatment conditions. Treatment interactions were also generally unimportant.

Solution aluminum and transpiration in Picea rubens and Gleditsia triacanthos seedlings.

Soil solution Al may contribute to red spruce (Picea rubens Sarg.) decline by inhibiting transpiration (Klein 1985). This study examines how Al affects transpiration in red spruce and honeylocust (Gleditsia triacanthos L.) seedlings and explores mechanisms for the observed responses. Red spruce seedlings were grown in dilute nutrient solutions containing 0 to 925 microM Al at pH 4.5 or 3.8. Solution Al had no effect on the transpiration, root hydraulic conductivity (K(r)) or shoot water potential (Psi) of red spruce. Transpiration of honeylocust was higher in the presence of 100 to 350 microM Al than 0, 500, or 600 microM Al. The Al-induced increases in transpiration of honeylocust were unrelated to shoot Psi or root K(r), but were closely correlated with the greater root lengths produced by intermediate levels of Al. In neither species was transpiration correlated with tissue concentrations of Al, P, K, Ca or Mg.

The influence of acid mists on growth, dry matter partitioning, nutrient concentrations and mycorrhizal fruiting bodies in red spruce seedlings.

Two-year-old spruce (Picea rubens Sarg.) seedlings were exposed to acid mists containing equimolar ammonium sulphate and nitric acid giving treatments of pH 2.5, 3.0 and 5.0. Acid mist treatments were applied twice weekly from late July until early October, 1987, when the plants were harvested. There were no significant differences in biomass accumulation or in height growth between treatments, but marked differences in root morphology were found. Significantly larger amounts of coarse roots were produced in the pH 5.0 acid mist treatment and plants in the pH 3.0 treatment produced significantly greater amounts of fine roots. Plants receiving acid mists of pH 3.0 or less had a greater frequency of fine root branches along their coarse roots. Production of mycorrhizal fruiting bodies of Thelephora terrestris Ehrenb.: Fr. was significantly greater (P < 0.001) at pH 5.0 than in the other treatments. Plants in the pH 2.5 and 3.0 treatments contained larger concentrations of N, 1.54 and 1.12% and S, 0.52 and 0.28% respectively, than those receiving acid mist at pH 5.0, i.e. 1.00 and 0.21% respectively. However, the between treatment differences of tissue nutrient concentrations were small relative to the differences in inputs between treatments. Foliar S exceeded concentrations recommended for nursery stock by 50 and 150% at pH 3.0 and 2.5 respectively.

Response of growth, photosynthesis, and mineral nutrition of red spruce seedlings to ozone and acidic cloud deposition

A field exclusion chamber study was established at a high elevation site in the Appalachian Mountains to determine the individual and combined effects of cloud water and ozone on the growth and physiological response of red spruce seedlings. Native seedlings from the study site, Whitetop Mountain, VA (1689 m), and seedlings grown from seed obtained from the Great Smoky Mountains in Tennessee were used in the study. Three replicates of the chamber treatments consisting of (1) exclusion of clouds and ozone, (2) exposure to ambient ozone with clouds removed, and (3) exposure to both ambient cloud and ozone were used in the study. Except for a statistically significant increase in current year needle biomass of native seedlings in treatments removing clouds or clouds and ozone, treatment effects were minimal. Periodic gas exchange measurements of seedlings taken throughout the growing season indicated that treatment-dependent effects on photosynthesis and respiration of both seedling types were few. Seedlings exposed to cloud moisture appeared to accumulate greater levels of N but not S. Increased nutrient leaching of foliar ions was not consistently observed, and soil exchangeable cations did not differ among treatments. These data do not indicate treatment-induced changes in seedling growth that would serve as primary cause(s) in recently reported red spruce decline at high elevations.

Response of red spruce seedlings to aluminum toxicity in nutrient solution: alterations in root anatomy

One year old red spruce (Picearubens Sarg.) were grown for 37 days in a nutrient solution containing 0, 50, 100, or 200 mg/L Al. No macroscopic evidence of Al injury was observed in the shoots of seedlings; however, Al toxicity symptoms were well developed in the roots. Aluminum reduced root length but increased root diameter and the number of cell layers in the root cap. Light and electron microscopic examination of root tips and segments 5–10 mm from the tip revealed numerous cellular changes in Al-stressed roots: premature vacuolation, accumulation of phenoliclike material, loss of cells from peripheral cell layers, formation of intercellular spaces, increased disruption of cellular membranes, and degeneration of the cytoplasm.

Growth Response and Drought Susceptibility of Red Spruce Seedlings Exposed to Simulated Acidic Rain and Ozone

Abstract One-year-old seedlings of red spruce were exposed to O3 (≤0.025 or 0.10 μl 1-1, 4 h d-1, 3 d wk-1) in combination with simulated rain (pH 5.6 or 3.0, 1 h d-1, 2 d wk-1, 0.75 cm h-1) for 10 weeks. After pollutant treatments, seedlings were subjected to two successive drought cycles. Whole-plant fresh weight increment (FWT) and dry weight were reduced after O3 exposure, whereas FWT and shoot height growth were increased after simulated rain exposure at pH 3.0 compared to pH 5.6. No interaction between O3 and rain treatments was observed for any growth variable measured. Foliar concentrations of K and S were greater in seedlings exposed to simulated rain at pH 3.0 compared with those at pH 5.6. Root hydraulic conductivity was highest in seedlings exposed to 0.10 μl 1-1 O3 + pH 3.0 rain solution compared with all other treatments after the first drought cycle. There were no significant O3 effects on net photosynthesis (Pn), transpiration or water-use efficiency prior to the drought cycles. However, during the second drought cycle, Pn was more sensitive to branch water potential in seedlings exposed to 0.10 μl 1-1 O3 + pH 3.0 solution compared with seedlings exposed to low O3 + pH 5.6 solution. For. Sci. 36(2):265-275.

Effects of ozone and acidic precipitation on the growth and photosynthesis of red spruce after two years of exposure

Although the agents responsible for the decline of red spruce on high elevation sites in the northeast are not known, 03 and acidic rain are considered to be possible contributing stresses. The research presented in this paper constitutes the second year of a 3-yr study to evaluate and quantify the influences of 03 and acidic precipitation on seedling red spruce. Two-year old red spruce seedlings were exposed to 03 at four levels (approximately 0.5, 1.0, 1.5, and 2.0 times ambient 03 concentration) and simulated acidic precipitation at three levels (pH 3.1, 4.1, and 5.1) in open-top chambers. The exposures occurred during June through October, 1988 after the seedlings had been exposed to the pollutants the previous year. At three intervals during the exposure period, seedlings were harvested and effects of the pollutant treatments were assessed by measuring the length of the 1988 terminal shoot, the number and length of branches, the dry mass of stems, needles, and roots, and rate of photosynthesis. There were no significant effects of 03 on any of the growth variables or on photosynthesis. There was a significant effect of pH on photosynthesis; rates of photosynthesis increased as acidity of the treatment increased. However, the higher rates of photosynthesis were not reflected in increased biomass of the seedlings. Significant 03 by pH interactions occurred for several growth variables.

Photosynthetic and stomatal conductance responses to acid mist of red spruce seedlings

Abstract Two‐year‐old seedlings of Picea rubens, growing in open‐top chambers in Scotland were treated twice weekly from July 1987 to December 1987, with mist containing ammonium sulphate and nitric acid at a pH of either 2.5 or 5.0. The response of photosynthesis and stomatal conductance to light flux density and carbon dioxide concentration were measured in March 1989. Leaf chlorophyll a and b contents were also measured. Acid mist (pH 2.5) resulted in several significant changes. First, both the rate of light saturated photosynthesis (Amax) and CO2‐ saturated rate of photosynthesis (J) were substantially increased, when expressed per unit leaf area. Second, the apparent quantum yield and chlorophylls a and b content increased. Third, as a consequence of the greater chlorophyll content of the leaves treated with acid mist, the rate of Amax, and J, expressed per unit chlorophyll, was substantially reduced in pH 2.5 treated branches. Stomatal conductance was enhanced at all but the highest light flux densities, and was independent of the CO2 concentration, remaining high for all values of CO2 concentration used. These results show that acid mist caused a number of responses in the gas exchange and photosynthetic properties of red spruce.

Response of Picea rubens seedlings to intermittent mist varying in acidity, and in concentrations of sulfur‐, and nitrogen‐containing pollutants

Two‐year‐old red spruce seedlings (Picea rubens Sarg.) growing in. field chambers were repeatedly exposed to acidic mist with a factorial combination of 3 fluctuating levels of acidity: median pH values of 3.0 (range of 2.5 to 3.5), 3.5 (range of 3.0 to 4.0), and 4.0 (range of 3.5 to 4.5). and 3 ion compositions: sulfate. nitrate and ammonium, and a combination of all 3 ions. The experiment was performed during the growing season over a period of 3.5 months. Mist exposures were intermittent with 5 wet‐dry cycles for each 16‐h overnight exposure period, Foliar necrosis occurred on seedlings treated with the most acidic mist and was most severe when the mist contained sulfate. At a median pH of 3.5, a value close to that of cloud water occurring in the eastern United States, injury developed with sulfuric acid mist, but not. when the mist contained nitric acid. The combination of high acidity and sulfate significantly decreased volume of aboveground tissues, while high acidity and nitrate increased volume. Root and needle dry weights were not affected. However, high acidity of mist was associated with increased leader shoot length. These results indicate, that there is a risk of foliar injury and changes in growth of red spruce with cloud water at a median acidity of pH 3.5 or below, especially when there are high concentrations of sulfate and low concentrations of nitrate.

Sensitivity of Tree Seedlings to Aluminum: III. Red Spruce and Loblolly Pine

AbstractUnexplained declines in the growth of both red spruce (Picea rubens Sarg.) and loblolly pine (Pinus taeda L.) have been reported within their natural ranges recently. The possible role of Al phytotoxicity as a causal agent in these declines has been studied extensively. Results of experiments with seedlings grown in solution, sand, and soil indicate minimal involvement of Al in the decline of loblolly pine. However, both controlled studies and field data indicate that reductions in tissue Ca and Mg may occur at Al concentrations well below those causing direct injury. Thus, Al may be involved in reductions in pine growth through interference with nutrient uptake and translocation. Several independent studies demonstrate that Al does directly affect growth of red spruce seedlings at Al concentrations of ≤0.25 mM, a concentration that might approach the range of soil solution Al concentrations measured in native red spruce stands in the Appalachian Mountains (0.1–0.28 mM). In these seedling studies, concentration of Ca and Mg in red spruce roots and foliage were also markedly reduced by relatively low solution Al concentrations. Thus, a contributing role for Al phytotoxicity in red spruce decline, through both direct biomass reduction and indirect effects due to interference with nutrient uptake, appears plausible.

Lead Mobility within the Xylem of Red Spruce Seedlings: Implications for the Development of Pollution Histories

AbstractDevelopment of Pb pollution histories using tree ring analyses has been troubled by possible mobility of Pb within stem xylem. In a 2‐yr study, we exposed red spruce (Picea rubens Sarg.) seedlings to Pb during one growing season, with Pb excluded in either the previous or following growing season. Lead levels within xylem rings and bark were subsequently determined using atomic absorption analyses. Lead concentrations in tissues from exposed seedlings were significantly higher than controls, and significant Pb concentrations were found in xylem formed during periods of Pb exclusion. Routes of Pb movement are uncertain, but were most likely acropetal from temporary storage sites in the roots.