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.     

Leaf nutrition and photosynthetic performance of sugar maple (Acer saccharum) in stands with contrasting health conditions

Leaf nutrition and photosynthetic performance of sugar maple (Acer saccharum Marsh.) were compared between two sugar maple stands in northwestern Vermont with contrasting health conditions as indicated by annual basal area growth, degree of crown dieback, and foliar appearance. Observations made during the diurnal cycle of both stands showed no apparent leaf water stress. In both stands, leaves had similar concentrations of major non-structural carbohydrates (starch and sucrose). Over two consecutive growing seasons (1991 and 1992), we consistently observed lower leaf Ca and Mg concentrations in the declining stand than in the healthy stand. Compared with the healthy stand, lower leaf chlorophyll concentrations and apparent leaf chlorosis were observed in the declining stand, and some trees had very low foliar Ca and Mg concentrations (0.31 +/- 0.03% and 0.09 +/- 0.01%, respectively). Trees in the declining stand had lower light-saturated net photosynthetic rates on a dry mass basis at both ambient CO(2) (P(n,amb)) and saturating CO(2) (P(n,sat)) than trees in the healthy stand. There were significant linear correlations between P(n,amb) and leaf mass per unit area (LMA) and between P(n,sat) per unit leaf area and LMA. There were also linear correlations between both P(n,amb) and P(n,sat) and leaf N when expressed on an area basis in both stands, indicating that variation in LMA may have been largely responsible for the observed photosynthesis-nitrogen relationship. The values of P(n,amb) and P(n,sat) were not significantly correlated with leaf N on a mass basis but were weakly correlated with leaf Ca and Mg on a mass basis. We conclude that low leaf Ca or Mg concentrations may limit leaf CO(2) assimilation and tree carbohydrate status in the declining stand.     

The successional status of sugar maple (Acer saccharum), revisited

Two complementary experimental designs at two contrasting scales (landscape/long term; individual tree/short term) were used for an in-depth evaluation of the successional status of sugar maple (AS: Acer saccharum Marsh.). First, forest disturbances during the 20th century and composition were mapped for two landscapes in the Du Lièvre watershed of southern Quebec. Our results show that, as well as dominating stands in the absence of fire, AS often rapidly developed dominance after fire, especially in the south of our study area. Similarly, a majority of AS-dominated stands clearcut in 1928 continued to be AS-dominated 60 years later. Second, we examined AS seedlings planted under two very contrasting light regimes. AS seedlings showed a combination of traits particularly adapted to tolerate shade under a low light regime. However, owing to a surprisingly high phenotypic plasticity, AS also exhibited efficient development under high light. This suggests the classification of AS as a late-successional species should indeed be revised and that generalist or trans-successional would be a more appropriate designation for this species. We discuss the ramifications of such a status revision, with an emphasis on the implications for its silviculture.     

Photosynthesis and water-use efficiency of sugar maple (Acer saccharum) in relation to pear thrips defoliation

An experimental introduction of pear thrips (Taeniothrips inconsequens Uzel), a major defoliator in sugar maple (Acer saccharum Marsh.) forests in northeastern North America, was conducted in a field plantation to determine if compensatory gas exchange occurs in response to feeding damage by this piercing-sucking insect. Sugar maple trees were enclosed in netting (167 micro m mesh) and pear thrips adults were introduced before leaf expansion in the spring. Pear thrips reduced whole-tree leaf area by approximately 23% and reduced leaf size (both mass and area) by 20% in the upper crown. Measurements of net CO(2) assimilation rate (A(net)) and stomatal conductance (g(s)) were made on tagged foliage that was later analyzed for stable carbon isotope composition (delta(13)C) to provide estimates of short- and long-term leaf water use efficiency (WUE). Pear thrips feeding reduced A(net) for fully expanded leaves by approximately 20%, although leaf chlorophyll content and leaf mass per unit area were apparently not affected. Comparison of A(net), g(s), instantaneous WUE and leaf delta(13)C between damaged and control trees as well as visibly undamaged versus moderately damaged foliage on pear thrips-infested trees indicated that there were no effects of pear thrips feeding damage on WUE or leaf delta(13)C. Long-term WUE among sugar maple trees in the field plantation, indicated by leaf delta(13)C analysis, was related to shorter-term estimates of leaf gas exchange behavior such as g(s) and calculated leaf intercellular CO(2) concentration (C(i)). We conclude that pear thrips feeding has no effect on leaf WUE, but at the defoliation levels in our experiment, it may reduce leaf A(net), as a result of direct tissue damage or through reduced g(s). Therefore, even small reductions in leaf A(net) by pear thrips feeding damage may have an important effect on the seasonal carbon balance of sugar maple when integrated over the entire growing season.     

Canopy photosynthesis of sugar maple (Acer saccharum): comparing big-leaf and multilayer extrapolations of leaf-level measurements

A comparison is made between a big-leaf model (i.e., without details of the canopy profile) and two multilayer models (i.e., with details of the canopy profile) to estimate daily canopy photosynthesis of a sugar maple (Acer saccharum Marsh.) stand. The first multilayer model uses the distribution of leaf area by leaf mass per unit area (LMA) classes, the observed relationships between the parameters of a photosynthesis-irradiance curve and LMA, and the relationship between relative irradiance and LMA to estimate canopy photosynthesis. When compared with this model, the big-leaf model underestimates daily canopy photosynthesis by 26% because of an assumed proportionality between photosynthetic capacity and relative irradiance, a proportionality that is inconsistent with our data. The bias induced by this assumption is reduced when the big-leaf model is compared with the second multilayer model which, in addition to the assumptions made for the first multilayer model, accounts for the sunlit and shaded fractions of leaf area. The residual bias is almost eliminated when the big-leaf model is run using a weekly averaged irradiance. It is likely, however, that this is the result of a compensating bias that, in this particular case, compensates for the initial bias introduced by the proportionality assumption. It is also shown that canopy photosynthesis can be represented by spatially inexplicit multilayer models that use leaf mass per area as a covariable to describe leaf characteristics and environment. Such models represent an interesting alternative to the biased big-leaf approach.     

Crown architecture of stand-grown sugar maple (Acer saccharum Marsh.) in the Adirondack Mountains

Leaf and crown morphology of shade-tolerant sugar maple (Acer saccharum Marsh.) were examined to test the hypotheses (1) that leaf area exhibits significant plasticity both within and between crown classes and individual tree crowns and (2) that leaf area is accurately predicted from estimates of crown volume. A total of 18 trees, ranging from 3.3 to 43.4 cm dbh, were felled and dissected into upper, middle, lower, and below-crown layers, for measurements of leaf, bark, and xylem dimensions. For dominant trees only, bark thickness and xylem radii were higher within the crown than below the crown. Cumulative leaf area index increased with decreasing stratum height at similar rates in all trees, except for two trees that were located in the understory. Area leaf weight declined with decreasing stratum height within the crown of all except four overstory trees. These four trees showed an increase with decreasing stratum height, i.e., leaves were heavier per unit area in the lower crown stratum and below the crown than they were at mid-crown. Within-tree leaf area density was usually higher in the upper crown of overstory trees and in the lower crown of understory trees. Total crown volume was the best predictor of whole-tree leaf area, but it was only slightly better than dbh.     

Responses of secondary chemicals in sugar maple (Acer saccharum) seedlings to UV-B, springtime warming and nitrogen additions

Anticipated effects of climate change involve complex interactions in the field. To assess the effects of springtime warming, ambient ultraviolet-B radiation (UV-B) and nitrogen fertilization on the foliar chemistry and herbivore activity of native sugar maple (Acer saccharum Marsh.) seedlings, we carried out a field experiment for 2 years at two sugar maple forests growing on soils of contrasting acidity. At the Oliver site, soils are derived from a strongly calcareous till, whereas the naturally acidic soils and base-poor soils of the Haliburton site are derived from the largely granitic Precambrian Shield. At both sites, removal of ambient UV-B led to increases in chlorogenic acid and some flavonoids and reduced herbivore activity. At Haliburton, ammonium nitrate fertilization led to further increases in foliar manganese (Mn), whereas at Oliver there were no such changes. Nitrogen additions led to decreases in the concentrations of some flavonoids at both sites, but seedlings at Oliver had significantly higher concentrations of flavonoids and chlorogenic acid than seedlings at Haliburton. We suggest that this could be associated with increased mobilization of Mn due to increased soil acidity, which interferes with the role of calcium (Ca) in the phenolic biosynthetic pathway. It appears that the composition of the forest soil governs the response of seedlings when they are exposed to abiotic stressors.     

Sticker stain formation in hardwoods: Isolation of scopoletin from sugar maple (Acer saccharum Marsh.)

Summary The extractives of clear and sticker stained sapwood from sugar maple (Acer saccharum Marsh.) were isolated and screened for low molecular-weight phenols, which could be involved in the formation of sticker stain. Scopoletin (7-hydroxy-6-methoxycoumarin) was identified as the major low molecular-weight free phenol in the samples studied. This compound, which has not previously been reported in extractives from maple wood, was quantified in stained and clear samples. Additionally, the two major fatty acids present were identified as palmitic acid and linolenic acid, and the two major sterols as stigmasterol and sitosterol.The authors are indebted to Mr. Peter Garrahan for provision of wood samples and the Canadian Forestry Service for financial support     

Water vapour diffusion and adsorption characteristics of sugar maple (Acer saccharum,Marsh.) wood polymer composites

Summary Water vapour diffusion characteristics and adsorption isotherms were determined for cell-lumen and cell-wall treated wood polymer composites (WPC). The diffusion coefficients of the cell-lumen WPC were lower than untreated wood and the cell-wall WPC coefficients were lower than cell-lumen. Using the Hailwood and Horrobin sorption model, it was found that the unimolecular layer is formed at lower moisture contents in WPC than in wood. The amount of free dissolved water was reduced only in the cell-wall WPC. The polymer reduces the water vapour accessibility in both types of WPC.     

Seasonal variation in biomass and carbohydrate partitioning of understory sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) seedlings

We investigated seasonal patterns of biomass and carbohydrate partitioning in relation to shoot growth phenology in two age classes of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.) seedlings growing in the understory of a partially harvested forest. The high root:shoot biomass ratio and carbohydrate concentration of sugar maple are characteristic of species with truncated growth patterns (i.e., cessation of aboveground shoot growth early in the growing season), a conservative growth strategy and high shade tolerance. The low root:shoot biomass ratio and carbohydrate concentration of yellow birch are characteristic of species with continuous growth patterns, an opportunistic growth strategy and low shade tolerance. In both species, starch represented up to 95% of total nonstructural carbohydrates and was mainly found in the roots. Contrary to our hypothesis, interspecific differences in shoot growth phenology (i.e., continuous versus truncated) did not result in differences in seasonal patterns of carbohydrate partitioning. Our results help explain the niche differentiation between sugar maple and yellow birch in temperate, deciduous understory forests.     

Root carbohydrate reserves, mineral nutrient concentrations and biomass in a healthy and a declining sugar maple (Acer saccharum) stand

Soil and root characteristics were contrasted between a "declining" and a "healthy" sugar maple (Acer saccharum Marsh.) stand in Vermont, USA. The declining stand had lower basal area increment and more crown dieback than the healthy stand. Soil pH and base cation content were lower and soil water content was higher at the site of the declining stand than at the site of the healthy stand, whereas soil temperature did not differ significantly between the sites. In live fine roots, concentrations of K and Ca were marginally (P < 0.07) lower in the declining than in the healthy stand, whereas concentrations of N, P, Mg, and Al were not significantly different (P = 0.13 to 0.87) between stands. Starch and soluble sugar concentrations of fine and coarse roots did not differ significantly between stands, indicating that crown dieback did not affect carbohydrate supply to the roots in the declining stand. Throughout the growing season, the standing live and dead root biomass were significantly higher in the declining stand than in the healthy stand, indicating that more carbon was allocated to roots and that root turnover was higher in the declining stand than in the healthy stand.     

Influence of overstory density on ecophysiology of red oak (Quercus rubra) and sugar maple (Acer saccharum) seedlings in central Ontario shelterwoods

A field experiment was established in a second-growth hardwood forest dominated by red oak (Quercus rubra L.) to examine the effects of shelterwood overstory density on leaf gas exchange and seedling water status of planted red oak, naturally regenerated red oak and sugar maple (Acer saccharum Marsh.) seedlings during the first growing season following harvest. Canopy cover of uncut control stands and moderate and light shelterwoods averaged 97, 80 and 49%, respectively. Understory light and vapor pressure deficit (VPD) strongly influenced gas exchange responses to overstory reduction. Increased irradiance beneath the shelterwoods significantly increased net photosynthesis (P(n)) and leaf conductance to water vapor (G(wv)) of red oak and maple seedlings; however, P(n) and G(wv) of planted and naturally regenerated red oak seedlings were two to three times higher than those of sugar maple seedlings in both partial harvest treatments, due in large part to decreased stomatal limitation of gas exchange in red oak as a result of increased VPD in the shelterwoods. In both species, seedling water status was higher in the partial harvest treatments, as reflected by the higher predawn leaf water potential and seedling water-use efficiency in seedlings in shelterwoods than in uncut stands. Within a treatment, planted and natural red oak seedlings exhibited similar leaf gas exchange rates and water status, indicating little adverse physiological effect of transplanting. We conclude that the use of shelterwoods favors photosynthetic potential of red oak over sugar maple, and should improve red oak regeneration in Ontario.     

Growth and provenance of Norway maple (Acer platanoides) in lowland Britain

The results of an experiment to investigate the early growthand form of ten different provenances of Norway maple (Acerplatanoides L.) are described. Two sites were planted and after8 years survival was 88 per cent and 95 per cent and heightincrement was 402 cm and 201 cm; confirmmg the potential ofNorway maple to be a productive forest tree. Provenances thatperformed well were from Germany, the Netherlands, Denmark andYugoslavia; exact locations were not known for all seed collections.A provenance from Russia was included, material from this fareast has rarely been tested in Britain. However, as expected,its performance was relatively poor. The main constraint tofurther planting of Norway maple is the palatability of thebark to grey squirrels (Sciurus carolinensis Gmelin.). However,it is a useful tree for high pH and heavy soils and as an alternativespecies to sycamore (Acer pseudoplatanus L.).     

Induction of tolerance to desiccation and cryopreservation in silver maple (Acer saccharinum) embryonic axes

Twenty percent of of the world's flowering plants produce recalcitrant seeds (i.e., seeds that cannot withstand drying or freezing). We investigated whether the embryonic axis from the normally recalcitrant seeds of silver maple (Acer saccharinum L.) can be made tolerant to desiccation (10% water content) and low temperature (-196 degrees C, cryopreservation) by pretreatment with ABA or the compound tetcyclacis, which enhances endogenous ABA concentrations. Pretreatment of axes with both ABA and tetcyclacis increased germination after desiccation and freezing to 55% from a control value of zero. Pretreatment of axes with ABA and tetcyclacis increased the ABA content of the axes, as measured by enzyme-linked immunoassay, and stimulated the synthesis of storage and dehydrin-like proteins, believed to have a role in the desiccation tolerance of orthodox seeds.     

Effects of soil compaction on growth variables in Cappadocian maple(Acer cappadocicum) seedlings

This study investigates the effects of increasing soil penetration resistance(SPR) on seedling morphology and seedling architecture. When seedlings of deciduous Cappadocian maple(Acer cappadocicum Gled.) were grown in a greenhouse in a loamy soil under a wide range of soil compactions, all morphological variables studied changed significantly with increasing SPR. The relationships between increasing SPR and all morphological responses except lateral root length followed a negative quadratic curve. All biomass variables except lateral root biomass showed a bell-shaped response with respect to SPR, with a maximum biomass variable between 0.6 and1.2 MPa, decreasing at higher soil compaction values. All allocation ratios were significantly affected by soil penetration resistance. Biomass allocation to roots was also affected by soil compaction. There was not a significant relationship between the specific stem length and increasing soil penetration resistance. The specific root length showed two trends to increasing SPR; it first decreased in response to the moderate compaction treatment(up to about 1.2 MPa), then increased significantly. We concluded that increasing soil compaction caused morphological changes to root and shoot sections of A.cappadocicum seedlings.     

Effect of measurement CO(2) concentration on sugar maple root respiration

Accurate estimates of root respiration are crucial to predicting belowground C cycling in forest ecosystems. Inhibition of respiration has been reported as a short-term response of plant tissue to elevated measurement [CO(2)]. We sought to determine if measurement [CO(2)] affected root respiration in samples from mature sugar maple (Acer saccharum Marsh.) forests and to assess possible errors associated with root respiration measurements made at [CO(2)]s lower than that typical of the soil atmosphere. Root respiration was measured as both CO(2) production and O(2) consumption on excised fine roots ( 20,000 micro l l(-1). Root respiration was significantly affected by the [CO(2)] at which measurements were made for both CO(2) production and O(2) consumption. Root respiration was most sensitive to [CO(2)] near and below normal soil concentrations (< 1500 micro l l(-1)). Respiration rates changed little at [CO(2)]s above 3000 micro l l(-1) and were essentially constant above 6000 micro l l(-1) CO(2). These findings call into question estimates of root respiration made at or near atmospheric [CO(2)], suggesting that they overestimate actual rates in the soil. Our results indicate that sugar maple root respiration at atmospheric [CO(2)] (350 micro l l(-1)) is about 139% of that at soil [CO(2)]. Although the causal mechanism remains unknown, the increase in root respiration at low measurement [CO(2)] is significant and should be accounted for when estimating or modeling root respiration. Until the direct effect of [CO(2)] on root respiration is fully understood, we recommend making measurements at a [CO(2)] representative of, or higher than, soil [CO(2)]. In all cases, the [CO(2)] at which measurements are made and the [CO(2)] typical of the soil atmosphere should be reported.     

Compositional and structural differences in two laurel forest stands (windward and leeward) on Tenerife, Canary Islands

The laurel forest of Anaga is the most emblematic community of the Canarian Archipelago. Restoration programs are being developed to increase laurel forest area on the island of Tenerife. Structural and spatial characteristics determine many aspects of the community, including regeneration patterns, disturbance level, stand history. In spite of the importance of this information for restoration, few quantitative studies have been conducted on laurel forest dynamics. We analyzed two stands of the Anaga laurel forest of different aspect. The main difference between the two sites was the wind exposure, one leeward and the other windward. Regeneration, spatial distribution of regeneration, tree species composition, asexual regeneration and environmental parameters were analyzed in three 50 × 50 m plots at each site. Both sites differ in important aspects such as species richness, species composition, asexual regeneration and dead tree composition, while they are not different in basal area, density, density of regeneration and density of dead trees. Both sites have had similar management in the last century. Asexual regeneration is able to maintain the present species composition, while sexual regeneration is able to offer future changes in the canopy composition. Regeneration strategies and the effect of some environmental characteristics should be considered in restoration programs.     

Effects of shade on growth and mortality of maple (Acer pseudoplatanus), ash (Fraxinus excelsior) and beech (Fagus sylvatica) saplings

We compared shade tolerance of maple, ash and beech in the saplingstage from two sites with rich soils differing in water supply,growing in dense thickets underneath a beech shelterwood ofvarying canopy densities. Shade tolerance was described by twocomponents: mortality in shade and height growth in high light.At low light, beech showed the least mortality, maple the highestand ash in between on both sites. The decline with increasinglight was steepest in beech and more gradual with ash and maple.At 15 per cent above canopy light, all three species approachedzero mortality. Beech as the most shade-tolerant species hadthe highest survival rate under low light and the least lengthgrowth rate under high light (>17 per cent). Ash had a lowersurvival rate at low light than beech and a highest growth rateat high light. Maple showed a bit weaker trade-off with thelowest survival rate but a growth rate inferior to ash. On thebetter water-supplied site, height growth was significantlysuperior in all three species only under high light. On thebasis of these results, silvicultural conclusions are drawnwith respect to appropriate light levels and cutting types.     

Inhibition and acclimation of C(3) photosynthesis to moderate heat: a perspective from thermally contrasting genotypes of Acer rubrum (red maple)

Effects of moderate heat on growth and photosynthesis were investigated in two clonal genotypes of Acer rubrum L., originally collected from the thermally contrasting habitats of Florida and Minnesota, USA, and known in the horticultural trade for sensitivity and insensitivity to heat, respectively. Under both common garden and warm greenhouse conditions (day/night temperature of 33/25 degrees C), the Florida genotype exhibited more growth than the Minnesota genotype. To determine the physiological parameters associated with this response, plants were acclimated to ambient (27/25 degrees C) or moderately elevated (33/25 degrees C) temperatures for 21 days before measurement of net photosynthesis at temperatures ranging from 25 to 48 degrees C. In vivo measurements of gas exchange and chlorophyll a fluorescence of ambient-acclimated plants revealed that, compared with the Minnesota genotype, the Florida genotype maintained a higher photosynthetic rate, higher stomatal conductance, more open PSII reaction centers, a greater PSII quantum yield and a lower quantum requirement for photosystem II (phi(PSII)) per mole of CO(2) fixed (phi(CO(2) )) throughout the measurement temperature range. When both genotypes were acclimated at 33/25 degrees C and measured at 33 degrees C, analysis of the response of net photosynthesis to calculated intercellular CO(2) concentration indicated that the maximal rate of Rubisco carboxylation (V(cmax)) decreased more in the Minnesota genotype than in the Florida genotype in response to elevated temperature. Additionally, phi(PSII)/phi(CO(2) ) at 33 degrees C was markedly higher for Minnesota plants under photorespiratory conditions, but similar to Florida plants under non-photorespiratory conditions. The results indicate that the higher net photosynthetic rate at 33/25 degrees C of the Florida genotype compared with the Minnesota genotype could be a result of several mechanisms, including the maintenance of a higher V(cmax )and a more efficient quantum requirement of PSII per mole of CO(2) fixed, which is likely the result of lower photorespiration.     

Flowering behavior of clones in a Norway maple (Acer platanoides) seed orchard and mating system analysis using nuclear SSR markers

European Journal of Forest Research - Norway maple (Acer platanoides L.) is a tree species native to Central Europe and occurs in scattered or in small populations mixed with other tree species....