Sugar Maple Seedlings Research Articles

Effects of Management on the Composition and Structure of Northern Hardwood Forests in Upper Michigan

Abstract To improve our understanding of how management affects the composition and structure of northern hardwood forests, we compared managed with unmanaged sugar maple (Acer saccharum Marsh.) dominated forests. Unmanaged old-growth and unmanaged second-growth forests provided baselines for comparing the effects of even-aged and uneven-aged forest management on selected aspects of biological diversity. Three replications of each condition were located on the Winegar Moraine in Michigan's Upper Peninsula. Old-growth forests were multistoried, dominated by a few, large trees with well-developed crowns extending over a subcanopy stratum 10–15 m in height and an abundance of woody vegetation (mostly sugar maple seedlings) at 2–3 m. This complex stand structure contrasts with the relatively uniform structure of unmanaged second-growth forests with a closed overstory canopy and limited understory development. Forest management, both even- and uneven-aged, created forest structures that were more complex than their unmanaged second-growth baselines, yet managed forests lacked some of the structural complexity characteristic of old-growth. Managed forests had fewer large trees (stem diameter at 1.37 m > 50 cm) and considerably less basal area in dead trees when compared with old-growth. There were fewer tree species in managed forests because commercially important tree species were favored for retention and, when present, early successional species (e.g., Populus grandidentata Michx., Populus tremuloides Michx.) were harvested. A subcanopy comprised of large shrubs and small trees characteristic of old growth was absent in managed forests, but this structural element may develop with time under management. As expected, thinning the overstory and disturbing the forest floor through tree harvesting promoted understory development in managed forests. Most of the added species, however, were common in the landscape and thus added little to overall species richness. FOR. SCI.48(1):129–145.

Age Structure and Regeneration Dynamics of Sugar Maple at the Deciduous/Boreal Forest Ecotone, Ontario, Canada

Sugar maple reaches its northern limit along the eastern shore of Lake Superior marking the transition from the deciduous forest of eastern North America to a predominantly boreal forest community. In light of regional warming trends over the past 100 years and projections for even warmer conditions in the future, we sought to characterize the current age structure and regeneration status of both sugar maple and boreal tree species within this ecotone zone. Within Lake Superior Provincial Park (Ontario, Canada), a series of east-west trending hills create numerous deciduous-boreal transition zones as sugar maple occupies uplands and boreal species occupy valley bottoms; then, once north of the sugar maple limit, boreal species dominate all topographic positions. Unlogged forest stands were sampled in the transition zone on ridges and slopes both north and south of the sugar maple limit. Overall tree density and basal area in sugar maple and boreal stands were similar across the ecotone, but seedling density was significantly higher in plots dominated by sugar maple. Moreover, sugar maple seedlings, but not saplings, were found slightly beyond the adult sugar maple tree hillside limit, indicating that the potential for range expansion may be limited by microclimatic variables, namely cold air drainage.

Trace Metal Detection by X-ray Microanalysis in Vascular Cells of Roots and Leaves from Field-Grown Sugar Maple Seedlings

The low survival of sugar maple (Acer saccharum) seedlings growing in unglaciated acidic forest soils (pH<4.0) in north-central Pennsylvania may be due in part to aluminum (Al) or manganese (Mn) phytotoxicity. Although foliar analysis has shown high concentrations (>2,000 ppm) of Mn, the location of potentially toxic elements in leaves or absorptive fine roots has not been studied in field-grown seedlings. This study of vascular (xylem and phloem) cells was conducted to determine by energy-dispersive X-ray microanalysis (EDX) whether Mn and/or Al could be detected in fine root or leaf midvein vascular cells. A secondary objective was to determine if vascular cells prepared by chemical fixation (CF) for conventional TEM or by freeze-substitution (FS) for EDX showed similar ultrastructural characteristics.Four sugar maple seedlings from an unglaciated field site (Potter County PA) were excavated, and roots were washed carefully. Two mm-long segments of fine roots and leaf midveins from each seedling were immersed in 3% glutaraldehyde for 6 hours, transferred to 0.1 M phosphate buffer, and transported to the Delaware Research Lab where tissues were post-fixed in OsO4 (in buffer), dehydrated in ethanol, and embedded in PolyBed-Araldite epoxy resin (CF method).

The Sugar Maple Story: Collaborative Research with Extension Agents and Growers

Abstract In collaboration with maple producers and cooperative extension agents in New York State and Pennsylvania, we conducted an outplanting trial of sugar maple seedlings selected for high sap sugar content. In addition to providing data about seedling survival and cultivation practices, the trials served as a focus for education efforts and strengthened partnerships between faculty and extension agents. For growers, the trials brought recognition and visibility, which some felt translated to marketing benefits, as well as opportunities to contribute to the maple industry and to enhance stewardship on their land.

Effects of elevated ozone and low light on diurnal and seasonal carbon gain in sugar maple

AbstractThe long‐term interactive effects of ozone and light on whole‐tree carbon balance of sugar maple (Acer saccharum Marsh.) seedlings were examined, with an emphasis on carbon acquisition, foliar partitioning into starch and soluble sugars, and allocation to growth. Sugar maple seedlings were fumigated with ambient, 1·7 × ambient and 3·0 × ambient ozone in open‐top chambers for 3 years under low and high light (15 and 35% full sunlight, respectively). Three years of ozone fumigation reduced the total biomass of seedlings in the low‐ and high‐light treatments by 64 and 41%, respectively, but had no effect on whole‐plant biomass allocation. Ozone had no effect on net photosynthesis until late in the growing season, with low‐light seedlings generally exhibiting more pronounced reductions in photosynthesis. The late‐season reduction in photosynthesis was not due to impaired stomatal function, but was associated more with accelerated senescence or senescence‐like injury. In contrast, the 3·0 × ambient ozone treatment immediately reduced diurnal starch accumulation in leaves by over 50% and increased partitioning of total non‐structural carbohydrates into soluble sugars, suggesting that injury repair processes may be maintaining photosynthesis in late spring and early summer at the expense of storage carbon. The results in the present study indicate that changes in leaf‐level photosynthesis may not accurately predict the growth response of sugar maple to ozone in different light environments. The larger reduction in seedling growth under low‐light conditions suggests that seedlings in gap or closed‐canopy environments are more susceptible to ozone than those in a clearing. Similarly, understanding the effects of tropospheric ozone on net carbon gain of a mature tree will require scaling of leaf‐level responses to heterogeneous light environments, where some leaves may be more susceptible than others.

Effect of manganese on endomycorrhizal sugar maple seedlings

Manganese (Mn) toxicity may play an important role in the poor survival of seedlings in declining sugar maple (Acer saccharum Marsh.) stands in northern Pennsylvania. To determine the effect of Mn on the growth of sugar maple seedlings, 1‐year‐old seedlings inoculated with vesicular‐arbuscular mycorrhizal (VAM) fungi and growing in sand‐vermiculite‐peat moss medium were irrigated for 7 weeks with nutrient solution (pH 5) containing 0.1 (control), 1, 2, 4, 8, or 16 mg L−1 Mn. Total seedling dry weight was negatively correlated with Mn, becoming significantly different than the control at 2 mg L−1 Mn. Stem and root dry weight were reduced by lower Mn levels than leaf dry weight. Manganese had no effect on the root/shoot ratio. The concentration of Mn in roots and leaves increased as the level of Mn in the nutrient solution increased, with the concentration in the leaves 2.2‐ to 3.7‐fold greater than the concentration in the roots. Except for a reduction of P in the roots, Mn had little effect on the concentration of nutrient elements in the roots or leaves. Colonization of the roots by VAM fungi was increased by Mn, with a maximum percentage at 4 mg L−1 Mn. Manganese toxicity symptoms in the leaves, small discrete chlorotic spots, began to appear at 1 mg L−1 Mn. The sensitivity of sugar maple seedlings to Mn found in this study supports the hypothesis that Mn may affect regeneration in declining sugar maple stands. However, evaluation of the effects of Mn on seedlings in native soils under field conditions will be necessary before the role of Mn in sugar maple regeneration can be understood.

Elevated C0 2 Does not Provide Protection against Ozone Considering the Activity of Several Antioxidant Enzymes in the Leaves of Sugar Maple

Summary Seedlings of sugar maple ( Acer saccharum Marsch.) were exposed for 46 days to 700 ppm of C0 2 , 200 ppb of ozone, and 700 ppm of C0 2 + 200 ppb of ozone. A significant increase in the activity of H 2 0 2 scavenging enzymes, i.e. ascorbate peroxidase [EC 1.11.1.11] and catalase [EC 1.11.1.6], was measured due to the action of 0 3 . This increase was rather negatively affected by elevated C0 2 . A tendency of decreased activity of glutathione reductase [EC 1.6.4.2] and superoxide dismutase [EC 1.15.1.1] due to the action of 0 3 was detected. Elevated C0 2 does not provide enhanced tolerance to oxidative stress in the seedlings of sugar maple. Changes in the activity of antioxidant enzymes were more pronounced in the young leaves (developed during the experiment) than in the old leaves (developed before starting the experiment). Stimulation of chloroplastic FeSOD by elevated C0 2 was observed, indicating oxidative stress in chloroplasts evoked by elevated C0 2 level. This effect did not result in enhanced protection against the detrimental effect of ozone, most probably due to compartmentation of C0 2 and 0 3 effects within the cell.

Influence of ozone on cold acclimation in sugar maple seedlings.

During summer 1994, sugar maple (Acer saccharum Marsh.) seedlings were grown in open-top chambers supplied with air containing near ambient ozone concentration (control, low O(3)) or three times the ambient ozone concentration (high O(3)). The rate of CO(2) assimilation was significantly reduced by chronic exposure to a high concentration of ozone during the summer. During fall, seedlings were removed from the open-top chambers and acclimated to cold under natural conditions. In both species during cold acclimation, the starch concentration decreased, whereas the sucrose concentration increased. There was no treatment effect on the freezing tolerance of roots, even though roots in the high-O(3) treatment accumulated higher concentrations of the cryoprotective oligosaccharides raffinose and stachyose than control roots. Cold acclimation occurred earlier and stachyose concentration of stems was higher in high-O(3)-treated seedlings than in low-O(3)-treated seedlings. Cold acclimation was associated with an earlier accumulation of ABA in the xylem sap of high-O(3)-treated seedlings compared with low-O(3)-treated seedlings.

Effects of elevated ozone on CO2 uptake and leaf structure in sugar maple under two light environments

The interactive effects of ozone and light on leaf structure, carbon dioxide uptake and short‐term carbon allocation of sugar maple (Acer saccharum Marsh.) seedlings were examined using gas exchange measurements and 14C‐macroautoradiographic techniques. Two‐year‐old sugar maple seedlings were fumigated from budbreak for 5 months with ambient or 3 × ambient ozone in open‐top chambers, receiving either 35% (high light) or 15% (low light) of full sunlight. Ozone accelerated leaf senescence, and reduced net photosynthesis, 14CO2 uptake and stomatal conductance, with the effects being most pronounced under low light. The proportion of intercellular space increased in leaves of seedlings grown under elevated ozone and low light, possibly enhancing the susceptibility of mesophyll cells to ozone by increasing the cumulative dose per mesophyll cell. Indeed, damage to spongy mesophyll cells in the elevated ozone × low light treatment was especially frequent. 14C macroautoradioraphy revealed heterogeneous uptake of 14CO2 in well defined areole regions, suggesting patchy stomatal behaviour in all treatments. However, in seedlings grown under elevated ozone and low light, the highest 14CO2 uptake occurred along larger veins, while interveinal regions exhibited little or no uptake. Although visible symptoms of ozone injury were not apparent in these seedlings, the cellular damage, reduced photosynthetic rates and reduced whole‐leaf chlorophyll levels corroborate the visual scaling of whole‐plant senescence, suggesting that the ozone × low light treatment accelerated senescence or senescence‐like injury in sugar maple.

A Case Study of Sugar Maple (Acer saccharum) as a Forest Seedling Bank Species

MARKS, P. L. AND S. GARDESCU (Section of Ecology & Systematics, Cornell University, Ithaca, NY 148532701, USA). A case study of sugar maple (Acer saccharum) as a forest seeding bank species. J. Torrey Bot. Soc. 125:287-296. 1998.-To examine the existence and behavior of a seedling bank, seedlings of sugar maple were censused for 24 years in a mixed-hardwood forest in central New York State. Each year we measured the heights of all sugar maple seedlings (individually-marked) in permanent plots. The population of seedlings persisted through time, with little net upward growth, in the shade. This seedling bank was maintained both by recruitment of new seedlings and by low annual mortality, with some sugar maple seedlings surviving > 30 years at < 1 m height. In an experimental canopy gap, long-suppressed sugar maple seedlings responded with substantial height growth. Thus, sugar maple exhibited the three defining characteristics for a seedling bank: a narrow range of heights in the shade, persistence in the shade, and retention of the capacity to grow rapidly upward once light availability increased.

Ultrastructure and Elemental Distribution in Foliage of Manganese-Treated Sugar Maple Seedlings: Comparison of Freeze-substitution Fixatives

Abstract Trace metals, such as manganese (Mn) and aluminum (Al), show increased solubility as soil acidity increases. Uptake of these elements may approach toxic concentrations in some plant species growing in acid forest soils. Previously, we had excellent results when chromium trioxide (CrO3) was used as the freeze substitution fixative in examining Al-treated plant and fungal tissue.1-2 However, when the fixative was used to study Mn toxicity, peak overlap (CrK β and MnKα) made it difficult to determine the location of Mn. In contrast, osmium tetroxide (OsO4) has no overlapping peak with Mn and is an excellent freeze substitution fixative. This study compares the use of OsO4 and CrO3 as fixatives for energy dispersive x-ray microanalysis (EDS) of the effect of Mn on ultrastructure and element localization in sugar maple leaves.

Liming influences growth and nutrient balances in sugar maple ( Acer saccharum) seedlings on an acidic forest soil

Forests in the northeastern US have been limed to mitigate soil acidification and the acidity of surface waters and to improve soil base cation status. Much of the area considered for liming is within the range of sugar maple ( Acer saccharum), but there is a poor understanding of how liming influences growth and nutrient balance of this species on sites that are not deficient in Ca. Of particular concern is the balance of K, a nutrient deficient in parts of the range of sugar maple and a deficiency linked with sugar maple decline in vigor. This buried pot study used soil that was low in K availability to test the influence of liming an acidic forest soil on biomass production and nutrient balance in 2-year-old sugar maple seedlings. The influence of surface applied lime and lime incorporated into the soil were compared with a control. Seedlings were planted on May 9 and were harvested on August 30. Plant parts were freeze-dried, weighed and analyzed for N, P, K, Ca, Mg, Al and Fe. In addition to concentrations, nutrient ratios and the diagnosis and recommendation integrated system (DRIS) were used to estimate nutrient balances. Although seedlings were similar in mass and dimensions at the start of the experiment, harvested seedlings were 37% larger in the incorporated treatment and 9% smaller in the surface limed treatment compared to control. Only fine roots showed no difference in mass among treatments. Seedlings from the incorporated treatment had greater foliar Ca ( P=0.002), K ( P=0.004) and P ( P=0.004) than the other treatments. There were no significant differences in foliar Mg, N, Fe or Al concentrations. At the end of the experiment, seedlings from the surface limed treatment contained 11% less K and 3% less P than control seedlings, while seedlings in the incorporated treatment contained 23% more K and 86% more P than in the control. Of the 14 nutrient ratios analyzed, four became more balanced and three became more imbalanced in the incorporated treatment and 10 nutrient ratios became more imbalanced and one ratio improved in the surface limed treatment compared to control. The DRIS indices showed that N was the most closely balanced nutrient relative to other nutrients and K was the most imbalanced nutrient in all treatments. Also, P was quite deficient while Ca, Mg and Fe were overabundant and Al was highly overabundant in all treatments. Surface liming exacerbated K, P and Al imbalances and nutrients remained similarly balanced in seedlings from the control and incorporated seedlings. This study suggested that liming acidic forest soils could intensify nutrient deficiencies, but that over the long term, the availability of highly deficient nutrients could improve.

Below-ground respiratory responses of sugar maple and red maple saplings to atmospheric CO2 enrichment and elevated air temperature

The research described in this paper represents a part of a much broader research project with the general objective of describing the effects of elevated [CO2] and temperature on tree growth, physiological processes, and ecosystem-level processes. The specific objective of this research was to examine the below-ground respiratory responses of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) seedlings to elevated atmospheric [CO2] and temperature. Red maple and sugar maple seedlings were planted in the ground in each of 12 open-top chambers and exposed from 1994 through 1997 to ambient air or air enriched with 30 Pa CO2,< in combination with ambient or elevated (+4 °C) air temperatures. Carbon dioxide efflux was measured around the base of the seedlings and from root-exclusion zones at intervals during 1995 and 1996 and early 1997. The CO2 efflux rates averaged 0.4 μmol CO2 m-2 s-1 in the root-exclusion zones and 0.75 μmol CO2 m-2 s-1 around the base of the seedlings. Mineral soil respiration in root-exclusion zones averaged 12% higher in the high temperature treatments than at ambient temperature, but was not affected by CO2 treatments. The fraction of total efflux attributable to root + rhizosphere respiration ranged from 14 to 61% in measurements made around red maple plants, and from 35 to 62% around sugar maple plants. Root respiration rates ranged from 0 to 0.94 μmol CO2 s-1 m-2 of soil surface in red maple and from 0 to 1.02 in sugar maple. In both 1995 and 1996 root respiration rates of red maple were highest in high-CO2 treatments and lowest in high temperature treatments. Specific red maple root respiration rates of excised roots from near the soil surface in 1996 were also highest under CO2 enrichment and lowest in high temperature treatments. In sugar maple the highest rates of CO2 efflux were from around the base of plants exposed to both high temperature and high-CO2, even though specific respiration rates were< lowest for this species under the high temperature and CO2 enrichment regime. In both species, patterns of response to treatments were similar in root respiration and root mass, indicating that the root respiration responses were due in part to differences in root mass. The results underscore the need for separating the processes occurring in the roots from those in the forest floor and mineral soil in order to increase our understanding of the effects of global climate change on carbon sequestration and cycling in the below-ground systems of forests.

Growth and morphological responses of yellow birch, sugar maple, and beech seedlings growing under a natural light gradient

Growth and morphological responses of yellow birch, sugar maple, and beech seedlings growing under a natural light gradient

Effects of Rodents on Survival of Tree Seeds and Seedlings Invading Old Fields

Tree invasion of old fields is an important process affecting landscape heterogeneity and species diversity, as well as the quality of wildlife habitat, in eastern North America. We examined the effects of tree seed and seedling predation by small mammals on the rate, spatial pattern, and species composition of tree invasion in old fields. We performed field experiments inside U-shaped enclosures built at forest–field edges, within which we manipulated the density of meadow voles (Microtus pennsylvanicus), which are major seedling predators. Although we did not directly manipulate density of white-footed mice (Peromyscus leucopus), which are major seed predators, mouse density was high wherever vole density was low. We introduced cohorts of seeds and seedlings of red maple (Acer rubrum) or sugar maple (Acer saccharum) [as specified in the Methods for each trial], white ash (Fraxinus americana), white pine (Pinus strobus), and tree-of-heaven (Ailanthus altissima), all common early invaders of old fields in our study area. Rates of seedling predation were higher in enclosures with higher density of voles, and voles showed distinct preferences for red maple, white ash, and Ailanthus over white pine. Predation rates on small seedlings were higher than on larger seedlings. Seedlings near the forest edge were killed at a lower rate than those >5 m into the field. Predation rates on seeds were higher in low-vole-density treatments, where mice were more abundant. Mice showed distinct preferences for white pine, avoided Ailanthus, and consumed sugar maple and white ash at intermediate rates. Predation rates on seeds were higher in shrub-dominated than in herbaceous old fields. Overall density of mice increased dramatically between 1994 and 1995, and seed predation rates increased concomitantly. In 1994, seed predation was most intense 5 m and 10 m into the field, and less intense at the forest–field edge and 20 m into the field; although a similar pattern was observed in 1995, the variation was not statistically significant. We conclude that both of these common small mammal species can have profound effects on survival of tree propagules near forest–field edges, but that their effects are strongly dependent on density. Voles had a strong, negative direct effect on seedling survival, but a positive indirect effect on seed survival by inhibiting seed predation by mice. Voles and mice: (1) showed distinctly different food preferences; (2) had their strongest effects at different positions with respect to the forest–field edge; and (3) had their strongest effects in different old-field types (herbaceous fields for voles, shrub-dominated fields for mice). These two species are not functionally redundant in their effects on old-field succession.

EFFECTS OF RODENTS ON SURVIVAL OF TREE SEEDS AND SEEDLINGS INVADING OLD FIELDS

Tree invasion of old fields is an important process affecting landscape het- erogeneity and species diversity, as well as the quality of wildlife habitat, in eastern North America. We examined the effects of tree seed and seedling predation by small mammals on the rate, spatial pattern, and species composition of tree invasion in old fields. We performed field experiments inside U-shaped enclosures built at forest-field edges, within which we manipulated the density of meadow voles (Microtus pennsylvanicus), which are major seedling predators. Although we did not directly manipulate density of white-footed mice (Peromyscus leucopus), which are major seed predators, mouse density was high wherever vole density was low. We introduced cohorts of seeds and seedlings of red maple (Acer rubrum) or sugar maple (Acer saccharum) (as specified in the Methods for each trial), white ash (Fraxinus americana), white pine (Pinus strobus), and tree-of-heaven (Ailanthus altissima), all common early invaders of old fields in our study area. Rates of seedling predation were higher in enclosures with higher density of voles, and voles showed distinct preferences for red maple, white ash, and Ailanthus over white pine. Predation rates on small seedlings were higher than on larger seedlings. Seedlings near the forest edge were killed at a lower rate than those >5 m into the field. Predation rates on seeds were higher in low-vole-density treatments, where mice were more abundant. Mice showed distinct preferences for white pine, avoided Ailanthus, and consumed sugar maple and white ash at intermediate rates. Predation rates on seeds were higher in shrub-dominated than in herbaceous old fields. Overall density of mice increased dramatically between 1994 and 1995, and seed predation rates increased concomitantly. In 1994, seed predation was most intense 5 m and 10 m into the field, and less intense at the forest-field edge and 20 m into the field; although a similar pattern was observed in 1995, the variation was not statistically significant. We conclude that both of these common small mammal species can have pro- found effects on survival of tree propagules near forest-field edges, but that their effects are strongly dependent on density. Voles had a strong, negative direct effect on seedling survival, but a positive indirect effect on seed survival by inhibiting seed predation by mice. Voles and mice: (1) showed distinctly different food preferences; (2) had their strong- est effects at different positions with respect to the forest-field edge; and (3) had their strongest effects in different old-field types (herbaceous fields for voles, shrub-dominated fields for mice). These two species are not functionally redundant in their effects on old- field succession.

The effects of ozone-exposed sugar maple seedlings on the biological performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.)

The effects of exposure of sugar maple (Acer saccharum Marsh.) to ozone on the entire larval stage of a native insect have not been previously investigated. This study reports the effects of sugar maple seedlings exposed to different ozone concentrations on the relative performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.). Three-year-old seedlings were set in nine open-top field chambers in the spring of 1992 and 1993. Three ozone concentrations were generated: charcoal-filtered ambient air (0×), ambient air (1×) and three times ambient air (3×). In 1992, female and male larval development time did not differ among ozone treatments. In 1993, female larvae reared on 3× developed faster than those on 0× and 1×, while male larvae were not affected. Ozone treatments did not influence pupal weights except for males in 1993 where pupae reared on 0× were heavier than 1× but did not differ from 3×. Larval and pupal survival rates were not affected by ozone in either year. Finally, 4th and 5th instar larvae showed a significant feeding preference for 3× foliage in 1993 but not in 1992. The response of the forest tent caterpillar to ozone exposed seedlings varied between years and could be more sensitive to annual climatic variations than ozone.

Simulated root dynamics of a 160-year-old sugar maple (Acer saccharum Marsh.) tree with and without ozone exposure using the TREGRO model.

Because of difficulties in directly assessing root responses of mature forest trees exposed to atmospheric pollutants, we have used the model TREGRO to analyze the effects of a 3- and a 10-year exposure to ozone (O(3)) on root dynamics of a simulated 160-year-old sugar maple (Acer saccharum Marsh.) tree. We used existing phenological, allometric, and growth data to parameterize TREGRO to produce a simulated 160-year-old tree. Simulations were based on literature values for sugar maple fine root production and senescence and the photosynthetic responses of sugar maple seedlings exposed to O(3) in open-top chambers. In the simulated 3-year exposure to O(3), 2 x ambient atmospheric O(3) concentrations reduced net carbon (C) gain of the 160-year-old tree. This reduction occurred in the C storage pools (total nonstructural carbohydrate, TNC), with most of the reduction occurring in coarse (woody) roots. Total fine root production and senescence were unaffected by the simulated 3-year exposure to O(3). However, extending the simulated O(3) exposure period to 10 years depleted the TNC pools of the coarse roots and reduced total fine root production. Similar reductions in TNC pools have been observed in forest-grown sugar maple trees exhibiting symptoms of stress. We conclude that modeling can aid in evaluating the belowground response of mature forest trees to atmospheric pollution stress and could indicate the potential for gradual deterioration of tree health under conditions of long-term stress, a situation similar to that underlying the decline of sugar maple trees.

Effect of soil base saturation and endomycorrhization on growth and nutrient status of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated partly with high soil exchangeable acidity and low base saturation on. A greenhouse experiment was set up to determine how growth and nutrient status of sugar maple seedlings can be influenced by soil acidification and the presence of an endomycorrhizal fungus. The experiment consisted of five levels of soil base saturation (from 12 to 50%) and two levels of soil inoculation by an endomycorrhizal fungus (inoculated and control) in a complete factorial arrangement Sugar maple seedlings were grown for 3 mo in the treated soil substrates. Seedling shoot elongation rate, growth [dry matter (TDM) mass, stem diameter, and total leaf area], and K, Ca and Mg concentrations in foliage and roots decreased with soil acidification with base saturation used as an indicator of the soil-acidification status. Foliar K and Ca level reached values below critical thresholds when soil base saturation was reduced to 12%. Under the experimental conditions, seedling growth was not significantly affected by endomycorrhization, except for root DM mass, which was reduced by 24% compared with the control treatment. For mycorrhizal seedlings, foliar Al concentration increased linearly from 113 mg kg−1 to 210 mg kg−1 with the reduction of soil base saturation from 50% to 12%, while, for non-mycorrhizal seedlings, foliar Al concentration remained at a high level (195 mg kg−1) independently of the soil acidification level. Sugar maple seedling growth was not related to accumulation of Al in foliage. The results of this experiment support the hypothesis that a causal relationship exists between the level of soil base saturation and the growth decrease and associated nutrient disorders observed in declining sugar maple stands in Quebec. Key words:Acer saccharum, nutrient status, seedling growth, soil base saturation, endomycorrhizae

Relationships between soluble sugar concentrations in roots and ecosystem stress for first year sugar maple seedlings

Accumulation of reducing sugars (i.e., glucose and fructose) in plant roots has been consistently correlated with forest dieback and decline and, therefore, has potential as a biological indicator of ecosystem stress. In this study, the relationships between acidic deposition and “natural” (temperature, mycorrhizae, and nutrition) factors with first-year sugar maple seedling root sugar concentrations and growth were assessed in two sugar maple dominated forests in Michigan. Seedlings at the southern site (Wellston) had greater root growth, phosphorus, total sugar, and sucrose concentrations in roots, but lower reducing sugar concentration in roots. In addition, percent root length colonized by vesicular-arbuscular mycorrhizal fungi was less than that found for seedlings growing at the northern site (Alberta). Throughfall deposition of nitrate, sulfate, and hydrogen ions was not significantly correlated with seedling total or reducing sugar concentration. Total sugar concentration in seedling roots was positively correlated with air and soil temperatures at the southern site, but not at the northern site. Seedling tissue phosphorus concentration was correlated with total sugars at both sites, with sucrose at the southern site, and reducing sugars at the northern site. Mycorrhizal colonization rates at the Alberta site were positively correlated with reducing sugar concentration in seedling roots and negatively correlated with sucrose concentration. The results suggest that differences in seedling root sugar concentrations in these two forests are related to seedling root growth and are most likely due to ecological variables, such as available soil phosphorus, temperature, and growing season length through some complex interaction with mycorrhizae rather than acidic deposition stress.