Acid mist and soil Ca and Al alter the mineral nutrition and physiology of red spruce

We examined the effects and potential interactions of acid mist and soil solution Ca and Al treatments on foliar cation concentrations, membrane-associated Ca (mCa), ion leaching, growth, carbon exchange, and cold tolerance of red spruce (Picea rubens Sarg.) saplings. Soil solution Ca additions increased foliar Ca and Zn concentrations, and increased rates of respiration early in the growing season (July). Soil Al treatment had a broad impact, reducing foliar concentrations of Ca, Mg, Mn, P and Zn, and resulting in smaller stem diameters, sapling heights and shoot lengths compared with soil treatments with no added Al. Aluminum treatment also reduced respiration when shoots were elongating in July and decreased net photosynthesis at the end of the growing season (September). Three lines of evidence suggest that Al-induced alterations in growth and physiology were independent of foliar Ca status: (1) Ca concentrations in foliage of Al-treated saplings were within the range of sufficiency established for red spruce; (2) mCa concentrations were unaffected by Al treatment; and (3) no Al x Ca interactions were detected. Acid mist treatment increased foliar Fe and K concentrations and increased leaching of Ca, Mg, Mn, Zn, Fe, and Al from foliage. Leaching losses of Ca were more than twice those of the element with the next highest amount of leaching (Zn), and probably led to the reductions in mCa concentration and membrane stability of acid-treated saplings. Acidic mist resulted in enhanced shoot growth, and consistent reductions in foliar cold tolerance in the fall and winter. Of the few significant interactions among treatments, most involved the influence of mist pH and Al treatment on foliar nutrition. In general, reductions in cation concentration associated with Al addition were greater for pH 5.0-treated saplings than for pH 3.0-treated saplings. We propose that H(+)-induced leaching of mCa from mesophyll cells is the mechanism underlying acid-induced reductions in foliar cold tolerance of red spruce.     

Influence of foliar N on foliar soluble sugars and starch of red spruce saplings exposed to ambient and elevated ozone

Red spruce (Picea rubens Sarg.) trees growing at high elevation in the northeastern United States have experienced decline in recent years but seedlings have proved to be relatively tolerant of a wide range of environmental stresses in controlled studies. One possible reason for the wide tolerance to stress in seedlings is their inherently large pool of carbohydrate reserves, which is available for maintenance during and regrowth after periods of stress. We tested for the effects of foliar N and exposure to ozone on foliar carbohydrate reserves of 20-year-old naturally regenerated saplings. The trees were maintained in native soil in 360-l containers for 5 years before the experiment. The year before the experiment, trees were fertilized with N,P,K to provide a population of trees from N deficient to N sufficient. As foliar N decreased below 0.9%, length of current-year shoots and specific needle area of current-year needles declined. Foliar N concentration was correlated with foliar sugar and starch concentrations, but relationships varied with time of year. Before bud break, foliar carbohydrates and N, in general, were positively correlated, and date of bud break was delayed in N-deficient trees. During active growth, foliar soluble sugars and N were positively correlated, but starch concentrations were negatively correlated with N. By late September, neither starch nor sugar concentration was correlated with N concentration. Ozone and foliar N concentrations did not interact to change foliar carbohydrate concentrations or shoot and needle growth in this relatively short-term study.     

Acclimation of Pacific yew (Taxus brevifolia) foliage to sun and shade

The success in clinical trials of the anti-cancer drug, Taxol(R), obtained from the bark of Pacific yew (Taxus brevifolia Nutt.), has raised interest in cultivation and regeneration of this little-known species. Pacific yew is shade-tolerant and it is not known whether the foliage can tolerate the high solar irradiances found on an open forest regeneration site or a nursery. Acclimation of Pacific yew to sun and shade was studied by comparing foliar physiology and morphology of male and female trees growing in full sun or shade. Interspecific foliar acclimation to sun was studied by comparing sun-grown English yew (Taxus baccata L.) with Pacific yew. No sex-specific acclimation was found in foliar physiology or morphology in either species. Sun-grown foliage of Pacific yew and English yew differed with respect to light harvesting, transpiration, stomatal conductance, leaf structure, stomatal distribution and foliar N concentrations and contents. Chlorophyll a fluorescence measurements indicated that shade-grown foliage of Pacific yew had larger and more efficient light harvesting systems than sun-grown foliage. Rates of CO(2) uptake and transpiration were similar in sun- and shade-grown foliage indicating acclimation of photosynthesis to the growth irradiance. Specific leaf area was significantly higher in shade-grown foliage of Pacific yew than in sun-grown foliage and was diagnostic of the light environment in which the foliage grew. Foliar N concentrations were not significantly different between sun- and shade-grown leaves of Pacific yew but sun-grown foliage had a higher N content. Physiological and morphological adjustments of Pacific yew foliage conferred tolerance to both high light and shade, enabling the trees to survive in a variety of light environments and indicating that Pacific yew is suited to nursery cultivation and regeneration of open sites.     

Effects of enhanced nitrogen deposition on foliar chemistry and physiological processes of forest trees at the Bear Brook Watershed in Maine

Effects of enhanced nitrogen deposition on nutrient foliar concentrations and net photosynthesis of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh) and red spruce (Picea rubens Sarg.) were evaluated at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired-watershed forest ecosystem study with one watershed treated since 1989 with bimonthly dry ammonium sulfate ((NH₄)₂SO₄) additions at a rate of 25.2 kg N ha⁻¹ year⁻¹, while the other watershed serves as a reference. The (NH₄)₂SO₄ treatment resulted in significant increases in foliar N concentrations for all three species and significant reductions in foliar Ca, Mg and Zn concentrations for American beech and red spruce. Treatment effects on foliar concentrations of other nutrients were not significant in any species. Despite higher N concentrations in all species, only treated sugar maple showed significantly higher photosynthetic rates. The non-response in net photosynthesis to higher foliar N in American beech and red spruce might be attributed to their low foliar Ca and/or Mg concentrations. Higher net photosynthetic rates in sugar maple might be explained by the higher foliar N and by the ability of this species to maintain an adequate Ca and Mg supply. Results suggested that nutrient imbalances due to inadequate supply of Ca and Mg might have counteracted a potential increase in net photosynthesis induced by higher N concentrations in American beech and red spruce.     

Rapid freezing induces winter injury symptomatology in red spruce foliage

Red spruce (Picea rubens Sarg.) suffers frequent and extensive injury to current-year foliage during the winter. Experimental freezing of red spruce foliage at cooling rates > 10 degrees C min(-1) induced visible symptomatology similar to natural winter injury at the branch, needle and cellular levels. Such damage was associated with a low-temperature exotherm near -10 to -12 degrees C, a loss in needle fluorescence, massive cellular disruption, foliar discoloration, and low needle survival. Susceptibility of individual trees to rapid freezing injury was associated with historical winter injury patterns and alterations in foliar nutrition. We conclude that anthropogenic deposition may alter the sensitivity of trees to winter injury caused by rapid temperature changes.     

Elevation dependent sensitivity of northern hardwoods to Ca addition at Hubbard Brook Experimental Forest,NH, USA

Acidic deposition has caused a depletion of calcium (Ca) in the northeastern forest soils. Wollastonite (Ca silicate) was added to watershed 1 (WS1) at the Hubbard Brook Experimental Forest (HBEF) in 1999 to evaluate its effects on various functions of the HBEF ecosystem. The effects of Ca addition on foliar soluble (extractable in 5% HClO₄) ions, chlorophyll, polyamines, and amino acids were studied in three hardwood species, namely sugar maple, yellow birch, and American beech. We further analyzed these effects in relation to elevation at Ca-supplemented WS1 and reference WS3 watersheds. Foliar soluble Ca increased significantly in all species at mid and high elevations at Ca-supplemented WS1. This was accompanied by increases in soluble P, chlorophyll, and two amino acids, glutamate and glycine. A decrease in known metabolic indicators of physiological stress (i.e., the amino acids, arginine and γ-aminobutyric acid (GABA), and the diamine, putrescine) was also observed. In general, these changes were species-specific and occurred in an elevation dependent manner. Despite an observed increase in Ca at high elevation for all three species, only sugar maple exhibited a decrease in foliar putrescine at this elevation indicating possible remediation from Ca deficiency. At higher elevations of the reference WS3 site, foliar concentrations of Ca and Mg, as well as Ca:Mn ratios were lower, whereas Al, putrescine, spermidine, and GABA were generally higher. Comparison of metabolic data from these three species reinforces the earlier findings that sugar maple is the most sensitive and American beech the least sensitive species to soil Ca limitation. Furthermore, there was an increase in sensitivity with an increase in elevation.     

Chlorophyll content monitoring in sugar maple (Acer saccharum)

We conducted two experiments to determine the usefulness of a chlorophyll content meter (CCM) for the measurement of foliar chlorophyll concentration in sugar maple (Acer saccharum Marsh.) in the fall color period. In Experiment 1, four sugar maple trees were visually assigned to each of four fall foliage color categories in October 1998. On four dates in the fall of 1999, leaves were taken from the trees and analyzed for chlorophyll concentration by absorbance of pigment extracts and by determination of the chlorophyll content index (CCI) with a CCM. The two measures of chlorophyll concentration were strongly correlated (P < 0.001, r2 = 0.72). In Experiment 2, the CCI of leaves from sugar maple trees subjected to one of four fertilization treatments (lime, lime + manure, lime + 10:10:10 N,P,K fertilizer and an untreated control) were determined with a CCM. Treatment effects were distinguishable between all pairwise comparisons (P < 0.001), except for the lime versus lime + NPK fertilizer treatments.     

Effects of chronically elevated nitrogen and sulfur deposition on sugar maple saplings: Nutrition,growth and physiology

At the Bear Brook Watershed in Maine (BBWM), we examined the effects of long-term experimentally elevated N and S deposition on foliar chemistry, growth, and photosynthetic capacity of sugar maple (Acer saccharum) saplings. The BBWM is a paired watershed system; one watershed has been acidified bimonthly with granular ammonium sulfate ((NH₄)₂SO₄) since 1989. The adjacent watershed is used as a reference. We observed a 56% increase in foliar Al and a 25% reduction in foliar Ca for sugar maple saplings on the treated watershed compared to reference. Foliar N (+15%), P (+10%), and K (+15%) were significantly elevated in treated saplings. Along with changes in foliar nutrients, there were significant differences in photosynthetic capacity.     

Element accumulation patterns of deciduous and evergreen tree seedlings on acid soils: implications for sensitivity to manganese toxicity

Foliar nutrient imbalances, including the hyperaccumulation of manganese (Mn), are correlated with symptoms of declining health in sensitive tree species growing on acidic forest soils. The objectives of this study were to: (1) compare foliar nutrient accumulation patterns of six deciduous (sugar maple (Acer saccharum Marsh.), red maple (Acer rubrum L.), red oak (Quercus rubra L.), white oak (Quercus alba L.), black cherry (Prunus serotina Ehrh.) and white ash (Fraxinus americana L.)) and three evergreen (eastern hemlock (Tsuga canadensis L.), white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss.)) tree species growing on acidic forest soils; and (2) examine how leaf phenology and other traits that distinguish evergreen and deciduous tree species influence foliar Mn accumulation rates and sensitivity to excess Mn. For the first objective, leaf samples of seedlings from five acidic, non-glaciated field sites on Pennsylvania's Allegheny Plateau were collected and analyzed for leaf element concentrations. In a second study, we examined growth and photosynthetic responses of seedlings exposed to excess Mn in sand culture. In field samples, Mn in deciduous foliage hyperaccumulated to concentrations more than twice as high as those found in evergreen needles. Among species, sugar maple was the most sensitive to excess Mn based on growth and photosynthetic measurements. Photosynthesis in red maple and red oak was also sensitive to excess Mn, whereas white oak, black cherry, white ash and the three evergreen species were tolerant of excess Mn. Among the nine species, relative rates of photosynthesis were negatively correlated with foliar Mn concentrations, suggesting that photosynthetic sensitivity to Mn is a function of its rate of accumulation in seedling foliage.     

Cold tolerance and water content of current-year red spruce foliage over two winter seasons

Red spruce (Picea rubens Sarg.) in high elevation forests of northeastern North America suffers from frequent and severe winter injury, leading to apical dieback, decreased growth, and high mortality. To examine the role of winter desiccation and freezing injury in winter damage, weekly assessments of cold tolerance and water content were made on current-year foliage collected from native red spruce trees at a high elevation site over two winter seasons. In both years, foliage maintained high water contents and adequate cold tolerance; nonetheless, slight to moderate injury was observed each year on some trees. Despite brief thaw periods each winter, no mid-winter dehardening sufficient to put foliage at risk of freezing injury was evident. These findings suggest that, at least in some years, winter injury to current-year red spruce foliage is produced by a mechanism other than desiccation or absolute low temperatures.     

Stem girdling manipulates leaf sugar concentrations and anthocyanin expression in sugar maple trees during autumn

To better understand the effects of sugar accumulation on red color development of foliage during autumn, we compared carbohydrate concentration, anthocyanin expression and xylem pressure potential of foliage on girdled versus non-girled (control) branches of 12 mature, open-grown sugar maple (Acer saccharum Marsh.) trees. Half of the study trees were known to exhibit mostly yellow foliar coloration and half historically displayed red coloration. Leaves from both girdled and control branches were harvested at peak color expression (i.e., little or no chlorophyll present). Disruption of phloem export by girdling increased foliar sucrose, glucose and fructose concentrations regardless of historical tree color patterns. Branch girdling also increased foliar anthocyanin expression from 50.4 to 66.7% in historically red trees and from 11.7 to 54.2% in historically yellow trees, the latter representing about a fivefold increase compared with control branches. Correlation analyses indicated a strong and consistent relationship between foliar red coloration and sugar concentrations, particularly glucose and fructose, in both girdled and control branches. Measures of xylem pressure potentials confirmed that girdling was a phloem-specific treatment and had no effect on water transport to distal leaves. Results indicate that stem girdling increased foliar sugar concentrations and enhanced anthocyanin expression during autumn in sugar maple foliage. Native environmental stresses (e.g., low autumn temperatures) that reduce phloem transport may promote similar physiological outcomes.     

Seasonal biochemical changes in coniferous forest canopies and their response to fertilization

Seasonal changes in concentrations of total nitrogen, free amino acids, chlorophyll, starch and sugar were measured in foliage from fertilized and unfertilized conifer forests in New Mexico and Oregon. In the New Mexico Douglas-fir (Pseudotsuga menziesii var glauca (Beissn.) Franco) forest, fertilization resulted in elevated foliar nitrogen concentrations on all dates, from an average of 9 mg g(-1) in unfertilized trees to 14 mg g(-1) in fertilized trees. In the Oregon western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest, fertilization increased total N by only 15%, from 13 mg g(-1) in unfertilized trees to 15 mg g(-1) in fertilized trees. Foliar nitrogen concentrations on a weight basis were lowest in winter and spring, but did not vary seasonally when expressed on a leaf area basis. Chlorophyll concentrations increased with fertilization and had greater seasonal variation than did total nitrogen concentrations. Chlorophyll concentrations were significantly higher during the growing season than in the winter and spring months. Fertilization did not result in major changes in the proportion of total nitrogen in chlorophyll at either the Oregon or the New Mexico site. Concentrations of free amino acids varied with date and fertilization treatment; in New Mexico, amino acids were highest in the winter sample, whereas in Oregon, they were lowest in winter and spring. At both sites, amino acid concentrations were significantly higher in fertilized trees than in control trees on most dates and the ratios of amino acid-N to total N were also significantly higher in fertilized trees. For both sites, starch concentrations were nearly zero for most of the year, but increased sharply just before bud break and initiation of new growth in the spring. Although fertilization resulted in increased nitrogen concentrations in foliage at both sites, the response in New Mexico was much greater than in Oregon. These results are in agreement with forest productivity data that suggest that growth in the New Mexico site is limited by nitrogen, whereas in the Oregon site it is not.     

Winter desiccation and injury of subalpine red spruce

Montane red spruce (Picea rubens Sarg.) in the northeastern United States has undergone a decline during the past two decades. One symptom associated with the decline syndrome is the episodic browning of first-year foliage in early spring. To examine the potential role of winter desiccation in this browning, the water relations of red spruce foliage in a subalpine forest on Mt. Moosilauke, New Hampshire, USA, were monitored from January to May, 1989. All sampled trees lost water during the winter and the first-year foliage on some trees turned brown in early spring. The relative water content of first-year shoots during the winter was a significant predictor of spring browning; red spruce trees that showed browning had desiccated faster and reached lower relative water contents. Damaged trees also had more closely packed needles and lower cuticular resistances to water loss. The first-year shoots had a significantly lower average relative water content than older shoots before and after browning. Cuticular resistance to water loss decreased with elevation. Sun-exposed shoots lost more water than shaded shoots because of solar heating of needles. Winter desiccation can occur before the decline-related spring browning of red spruce foliage.     

Accretion, partitioning and sequestration of calcium and aluminum in red spruce foliage: implications for tree health

Calcium (Ca) is an essential macronutrient in plants and is an important component of many cellular structures and physiological processes as well as overall forest function. Aluminum (Al) in soil solution can inhibit Ca uptake by plants and disrupt many Ca-dependent metabolic and physiological processes of plants. The ratio of Ca to Al in soil solution can be an important indicator of forest health, especially on acid soils. We used sequential chemical extractions (water, acetic acid and hydrochloric acid) to assess the chemical availability of Ca and Al in foliage from mature red spruce (Picea rubens Sarg.) trees growing under ambient environmental conditions. In plants deficient in Ca and with intermediate total foliar Ca concentration ([Ca]), Ca preferentially accrued in labile and physiologically available forms (water- and acetic acid-extractable). In plants with total foliar [Ca] above a "sufficiency" threshold, Ca also accrued in a chemically sequestered form with low solubility (HCl-extractable), suggesting that Ca sequestration is an inducible process in response to excess foliar Ca. Because it has low solubility, it is likely that sequestered Ca is unavailable for Ca-dependent physiological processes. Immobilization of Al in foliage was related to Ca sequestration, suggesting that Ca sequestration may provide a passive mechanism for Al tolerance in the foliage of these trees. Aluminum immobilization was evident based on the ratio of HCl-extractable Al to the more labile (water- and acetic acid-extractable) forms of Al. Sufficient labile Ca combined with Al sequestration was associated with plant health, including enhanced foliar accretion of Mg and Mn, greater tree growth, enhanced foliar cold hardiness and reduced winter injury. These findings demonstrate that not all chemical forms of foliar Ca and Al are of equal physiological significance and underscore the importance of assessing the biologically significant element forms in biogeochemical research.     

Rapid freezing injury in red spruce: seasonal changes in sensitivity and effects of temperature range

On calm, cold days in winter, sun-exposed needles of red spruce (Picea rubens Sarg.) may warm 10 to 20 degrees C above ambient air temperature, and undergo rapid (>/= 1 degrees C min(-1)) fluctuations in temperature as light breezes or passing clouds alter the energy balance of the foliage. It has been proposed that the resulting rapid freeze-thaw cycles (freezing stress) cause a type of winter injury in montane red spruce that is characterized by necrosis of sun-exposed foliage. In autumn and winter, we monitored rapid freezing stress response of needle sections from 10 montane red spruce trees by subjecting needles to rapid freezing over the temperature span typically recorded in the field. In autumn, experimental rapid freezing stress produced severe injury only at temperatures considerably lower than expected for that time of year. In winter, rapid freezing caused occasional, moderate injury in fully hardened foliage of trees susceptible to both slow and rapid freezing. Seasonal changes in sensitivity to rapid and slow freezing were correlated, suggesting that environmental factors that are known to affect sensitivity to slow freezing may also affect sensitivity to rapid freezing. Experimental manipulation of the start and end temperatures of rapid freezing stress events showed that moderate to severe needle injury can occur in susceptible trees at temperature spans slightly more extreme than those typically recorded in the field. The extent of injury was similar at different starting temperatures if rapid freezing occurred over the same temperature span. Year-old foliage was consistently less sensitive to rapid freezing stress than current-year foliage, but some year-old foliage was damaged when the rapid freezing stress regime caused severe injury in current-year foliage. We conclude that rapid freeze-thaw cycles can explain light to moderate injury of current-year foliage, but they do not explain the more severe and widespread pattern of foliar damage that has occurred intermittently over at least the last 18 years.     

Foliar delta(13)C and delta(18)O reveal differential physiological responses of canopy foliage to pre-planting weed control in a young spotted gum (Corymbia citriodora subsp. Variegata) plantation

Weed control may improve the growth of forest plantations by influencing soil water and nutrient availability, but our knowledge of leaf-level physiological responses to weed control at different within-canopy positions is limited for tropical and subtropical plantations. Foliar carbon (delta(13)C) and oxygen (delta(18)O) isotope compositions, gas exchange, and nitrogen (N(mass)) and phosphorus (P(mass)) concentrations at four canopy positions were assessed in a young spotted gum (Corymbia citriodora subsp. Variegata (F. Muell.) A.R. Bean & M.W. McDonald) plantation subjected to either weed control or no weed control treatment, to test if leaves at different positions within the tree canopy had the same physiological responses to the weed control treatment. Weed control increased foliar delta(13)C but lowered delta(18)O in the upper-outer and upper-inner canopy, indicating that weed control resulted in a higher foliar photosynthetic capacity at upper-canopy positions, a conclusion confirmed by gas exchange measurements. The increased photosynthetic capacity resulting from weed control can be explained by an increase in foliar N(mass). In the lower-outer canopy, weed control reduced foliar delta(13)C while lowering delta(18)O even more than in the upper-canopy, suggesting strong enhancement of the partial pressure of CO(2) in the leaf intercellular spaces and of foliar stomatal conductance in lower-canopy foliage. This conclusion was supported by gas exchange measurements. Foliar photosynthesis in the lower-inner canopy showed no significant response to weed control. The finding that leaves at different canopy positions differ in their physiological responses to weed control highlights the need to consider the canopy position effect when examining competition for soil nutrient and water resources between weeds and trees.     

Correlations between stable carbon-isotope abundance and hydraulic conductivity in Douglas-fir across a climate gradient in Oregon, USA

Stomatal conductance in trees is related to both foliar carbon-isotope abundance and stem hydraulic properties. By combining these relationships, I hypothesized that carbon-isotope abundance in foliage should vary with limitations to water movement through supporting branches. I sampled Douglas-fir branches (Pseudotsuga menziesii (Mirb.) Franco) from six sites across a climate gradient in Oregon, USA for foliar carbon-isotope abundance and stem hydraulic properties. I used a forest growth model to quantify climate-induced stomatal limitations, expressed as reduced potential transpiration, across the gradient. Foliar stable carbon-isotope abundance showed a strong inverse relationship with branch specific conductivity (hydraulic conductivity per unit functional sapwood area) and leaf-specific conductivity (hydraulic conductivity per unit leaf area). Foliar stable carbon-isotope abundance was correlated with modeled reductions in potential transpiration; however, the inclusion of leaf-specific conductivity improved the correlation by more than 30%. Combined, leaf-specific conductivity and climate-induced stomatal constraints explained 84% of the variation in foliar isotope abundance in 1994 foliage. This model was confirmed on foliage classes 1990-1993.     

Age-related changes in foliar morphology and physiology in red spruce and their influence on declining photosynthetic rates and productivity with tree age

The contribution of changes in meristem behavior to age-related decline in forest productivity is poorly understood. We studied age-related trends in needle morphology and gas exchange in a population of red spruce (Picea rubens Sarg.) growing in a multi-cohort stand where trees ranged from first-year germinants to trees over 150 years old, as well as in grafted scions from these trees. In the field study, age-related trends in foliar morphology were determined in six cohorts ranging in age from 2 to 120 years, and differences in gas exchange characteristics were compared between 60- and 120-year age classes. In a common-rootstock study, scions from trees representing 20-, 60-, and 120-year cohorts were grafted onto juvenile rootstock and maintained for three growing seasons, after which morphological and physiological foliar attributes were evaluated. The field study revealed significant age-related trends in foliar morphology, including decreasing specific leaf area, and increasing needle width, projected area, and width/length ratio. Similar trends were apparent in foliage from the grafted scions. Both in situ foliage and shoots of grafted scions from the oldest cohort showed significantly lower photosynthetic rates than their counterparts from younger trees; however, differences in stomatal conductance and internal CO(2) concentrations were not significant. These results suggest that: (1) foliage of red spruce exhibits age-related trends in both morphology and physiology; (2) age-related decreases in photosynthetic rates contribute to declining productivity in old red spruce; (3) declines in photosynthetic rates result from nonstomatal limitations; and (4) age-related changes in morphology and physiology are inherent in meristems and persist for at least 3 years in scions grafted to juvenile rootstock.     

Physiological implications of seasonal variation in membrane-associated calcium in red spruce mesophyll cells

We examined the pattern of seasonal variation in total foliar calcium (Ca) pools and plasma membrane-associated Ca (mCa) in mesophyll cells of current-year and 1-year-old needles of red spruce (Picea rubens Sarg.) and the relationship between mCa and total foliar Ca on an individual plant and seasonal basis. Foliar samples were collected from seedlings and analyzed on 16 dated at 2- to 3-week intervals between June 1994 and March 1995. Concentrations of mCa in current-year needles were more seasonally dynamic and responsive to temporal environmental changes than either mCa concentrations of 1-year-old needles, which were largely stable, or total foliar Ca concentrations in both tissues. In current-year needles, mCa was barely evident in early summer, increased steadily through summer, and then increased dramatically in early fall and surpassed the concentration in 1-year-old needles. Coincident with the first severe frost, mCa concentrations in current-year needles declined significantly and subsequently maintained concentrations comparable to those of 1-year-old needles. Following an extended January thaw, which included 5 days of minimum temperatures > 5 degrees C, mCa concentrations of current-year needles temporarily, but significantly, declined. However, there was no change in mCa concentrations of 1-year-old needles or total Ca concentrations of either tissue. Total Ca concentrations were stable through midsummer in both tissues, doubled in late summer, and then were stable in both tissues throughout fall and winter. Total Ca concentrations were consistently higher in 1-year-old than in current-year needles. Correlations between concentrations of mCa and total foliar Ca were consistently low and mostly nonsignificant. Thus, the dominant, but insoluble, extracellular Ca pool reflected in commonly measured total foliar Ca concentrations is not a meaningful surrogate for the physiologically important and labile pool associated with the plasma membrane-cell wall compartment of red spruce mesophyll cells. It is likely that shifts in the critical mCa compartment would not be detected by analysis of total foliar Ca pools. Seasonal changes in mCa concentration seemed to parallel seasonal changes in membrane structure, and possibly the important role of extracellular Ca in transducing messages associated with environmental signals.     

Spatial and temporal variability of foliar mineral concentration in beech (Fagus sylvatica) stands in northeastern France

Foliar mineral concentration may provide a basis for monitoring the consequences of long-term environmental changes, such as eutrophication and acidification of soils, or increase in atmospheric CO(2) concentration. However, analytical drifts and inter-tree and year-to-year variations may confound environmental effects on long-term changes in foliar mineral concentration. We have characterized the relative effects of these potentially confounding factors on foliar carbon, nitrogen, phosphorus, calcium, potassium, magnesium and manganese concentrations in 118 pure beech (Fagus sylvatica L.) stands, sampled in 1969-71 and 1996-97. Interannual fluctuations of these elements were quantified in a subset of six beech stands monitored for 5 years. Intercalibration between the methods used at each sampling period for nitrogen and phosphorus analyses showed significant, but low, relative differences (0.8 and 3.3% for N and P, respectively). Based on inter-tree variability, elements could be arranged in four groups: C (constant), N and P (low variability), K and Ca (medium variability), Mn and Mg (high variability). Inter-tree coefficients of variation were 2, 6, 8, 15, 18, 22 and 27%, respectively. Year-to-year fluctuations increased in the order N, P, Mg, K, Ca, and Mn coefficients of variation of 4, 4, 7, 9, 11, 15 and 29%, respectively). Between the two sampling periods, foliar N concentration increased 12%, whereas decreases were observed for P (-23%), Mg (-38%) and Ca (-16%). Ratios of N/P, N/K and N/Mg increased by 42, 19 and 77%, respectively. These changes were larger than the interannual variations for P, Mg, N/P, N/Mg and Mg/Ca. Decreasing concentrations of P and cations were particularly marked for trees growing on acidic soils, whereas the positive N trend did not depend on soil type. Both increasing atmospheric CO(2) concentrations and acidification of forest soils could contribute to decreasing P and cation concentrations in foliage. The increase in foliar N concentration with time suggests a nitrogen deposition effect. Whatever the causes of these changes, the large shift in element ratios indicates an accelerating imbalance between nitrogen and cation status.