Dendroclimatology of sugar maple (Acer saccharum): Climate-growth response in a late-successional species

Sugar maple (Acer saccharum) is a shade-tolerant, late successional dominant species in the North American eastern deciduous forest. The objective of this study was to quantify the relationship between climate and radial growth in sugar maple and to identify spatial and temporal patterns in dendroclimatic response. We used a combination of archived sugar maple tree-ring chronologies and newly sampled sites to calculate dendroclimatic response of sugar maple at 13 sites in the United States and Canada. At all sites, sugar maple growth was significantly correlated to monthly temperature, precipitation, or Palmer Drought Severity Index. However, there were no generalizable patterns in sugar maple’s growth response to climate. Individual sites had unique dendroclimatic responses with respect to: a) which climatic variables were correlated to radial growth; b) what months had significant correlations between climate and radial growth; and c) what years had significant correlations between climate and radial growth. The individualistic dendroclimatic response of sugar maple appears to reflect a plastic response of the species to changes in climate perhaps related to its status as a strong competitor in late-successional forests. This ability to survive a wide range of environmental conditions may bode well for the species persistence under variable future climatic conditions. It also points to the need for more research on late-successional species in examining forest response to potential climate change scenarios because these species may be more resilient than early-successional species.     

Plastic allometry in young sugar maple (Acer saccharum): adaptive responses to light availability

Age, height, number of shoot endings, neighbor density, and overhead cover from local neighbors were recorded for over 1, 400 young sugar maple trees under 200 cm tall and growing in open vs. closed (shaded) habitats from two sites. Up to about age 5 yr, seedlings increase in height but rarely branch. Once branching starts, there begins a general decrease with age in the number of centimeters of height added for every new shoot ending that is produced. The pattern of this allometric relationship, however, is plastic—in the closed habitats, this switch to increased branching relative to height growth is delayed compared with trees from the open habitats. Within the closed habitats, branching is also delayed for trees having dense cover from local neighboring understory vegetation compared with trees that are not overtopped by understory vegetation. The oldest and tallest unbranched seedlings were recorded from the closed habitats. Seedlings displaying the first branch, however, were younger in the open habitats than in the closed habitats, and at one site they were shorter in the open habitat than in the closed habitat. These results suggest that the allometric relationship between height and degree of branching can display adaptive plasticity depending on light availability: As competition for light decreases (with greater light availability), there is an increasing premium on lateral growth (branching) to maximize light interception. Conversely, as competition for light increases (under decreasing light availability), there is an increasing premium on vertical growth (through strong and persistent apical dominance) to minimize the chances of being overtopped by neighbors.     

Vesicular-arbuscular mycorrhizal spore populations in sugar maple (Acer saccharum marsh. L.) forests

 The numbers and types of spores of vesicular-arbuscular mycorrhizal fungi occurring in the top 15 cm of the soil in three maple forests in Eastern Canada were investigated using traditional wet-sieving/decanting methods. In the most acid site, at St. Hippolyte, Québec, where the soil had been amended with base cations, after 1 year there was no effect on the numbers of spores present. Vesicular-arbuscular mycorrhizal spores present at St. Hippolyte consisted of Glomus rubiforme, other Glomus spp. and Acaulospora spp. Although the sporocarpic species, G. aggregatum, G. macrocarpum and G. rubiforme occurred at St. Hippolyte, they were not found at the two less acid sites (Waterloo, Ontario and Lacolle, Québec) . Spores of Acaulospora spp. were found at all three sites, but were most abundant at St. Hippolyte. At St. Hippolyte the total number of spores was much higher than at the other two sites; at Waterloo numbers were an order of magnitude lower than at St. Hippolyte. It is suggested that G. rubiforme and Acaulospora species may be adapted to acid conditions. Seasonal patterns of spore abundance suggested that Acaulospora spp. may sporulate during the spring, whereas G. rubiforme may sporulate during the fall. Accepted: 6 September 1995     

Changes in protein synthesis during stratification and dormancy release in embryos of sugar maple (Acer saccharum)

Protein synthesis in dormant embryos of sugar maple ( Acer saccharum ) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [³⁵S]-methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the cotyledons.     

Hydraulic lift and its influence on the water content of the rhizosphere: an example from sugar maple,Acer saccharum

Hydraulic lift, the transport of water from deep in the soil through plant root systems into the drier upper soil layers, has been demonstrated in several woody plant species. Here the volume of water involved in hydraulic lift by a mature sugar maple tree is estimated. Twenty-four intact soil cores were collected from the vicinity of a sugar maple tree at the same positions at which thermocouple psychrometers had been placed. Desorption measurements were made on the soil cores and the data were fitted to the Campbell relation for soil matric potential versus soil water content . The psychrometer data were filtered to obtain the diurnal component contributed by hydraulic lift. The diurnal component in was combined with the Campbell relation for each soil core to obtain the increase in soil water content due to hydraulic lift. The additional water contents were numerically integrated to obtain a volume of 102±54 1 of water which was hydraulically lifted each night. The volume of hydraulically lifted water (HLW) is sufficiently great that in ecosystems where hydraulic lift occurs it should be included in models for calculating the water balance. However, a previous analysis of the stable hydrogen isotope composition (D) of water in understory plants around trees conducting hydraulic lift implies a much greater volume of HLW than that calculated from the analysis performed above. To reconcile these differences, it is hypothesized that some understory plants preferentially extract HLW due to its higher matric potential and that the proportion of this water source within the xylem sap of at least some understory plants that use HLW was so great that the roots of these plants must therefore be in close proximity to the tree roots from which the HLW comes. The results of this study have implications for studies of plant competition where positive associations may exist as well as for ion uptake, nutrient cycling and the design of agroforestry systems.     

Assessment of the potential role of metals in sugar maple (Acer saccharum Marsh) decline in Ontario, Canada

Spatial and temporal differences in the crown condition of sugar maple (Acer saccharum Marsh) in Ontario remain largely unexplained. In this study, the potential role of metals in sugar maple dieback was explored by measuring metal concentrations in foliage and forest floor (LFH) at 35 forest stands in south-central Ontario that exhibit varying levels of decline and span a climatic, soil acidity and acid deposition gradient. Foliar and forest floor metal concentrations varied among sites by between two and ten-fold, with acidic sites exhibiting the highest concentrations of many metals in the forest floor and foliage. Sites with moderate decline symptoms (decline index (DI)?>?10, averaged between 1986 and 2004) had significantly greater Cd, Zn, Cu, Pb and Mn concentrations and lower Ca concentrations in the forest floor compared with healthy sites (DI?<?10). Foliar concentrations of Cd, Sr and Mn were also significantly greater and Ca was significantly lower in sites with moderate decline symptoms compared with healthy sites. However the highest metal concentrations in foliage and the forest floor found in this study are lower than critical values reported in the literature. The notable exception is Mn where values at acidic sites may be high enough to negatively impact sugar maple.     

Seasonal nitrogen and carbon concentrations in white,brown and woody fine roots of sugar maple (Acer saccharum Marsh)

Small diameter (<1.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots.     

Influence of northern limit range on genetic diversity and structure in a widespread North American tree,sugar maple (Acer saccharum Marshall)

Due to climate change, the ranges of many North American tree species are expected to shift northward. Sugar maple (Acer saccharum Marshall) reaches its northern continuous distributional limit in northeastern North America at the transition between boreal mixed‐wood and temperate deciduous forests. We hypothesized that marginal fragmented northern populations from the boreal mixed wood would have a distinct pattern of genetic structure and diversity. We analyzed variation at 18 microsatellite loci from 23 populations distributed along three latitudinal transects (west, central, and east) that encompass the continuous–discontinuous species range. Each transect was divided into two zones, continuous (temperate deciduous) and discontinuous (boreal mixed wood), based on sugar maple stand abundance. Respective positive and negative relationships were found between the distance of each population to the northern limit (D_north), and allelic richness (A_R) and population differentiation (F_ST). These relations were tested for each transect separately; the pattern (discontinuous–continuous) remained significant only for the western transect. structure analysis revealed the presence of four clusters. The most northern populations of each transect were assigned to a distinct group. Asymmetrical gene flow occurred from the southern into the four northernmost populations. Southern populations in Québec may have originated from two different postglacial migration routes. No evidence was found to validate the hypothesis that northern populations were remnants of a larger population that had migrated further north of the species range after the retreat of the ice sheet. The northernmost sugar maple populations possibly originated from long‐distance dispersal.     

Patterns of rhizosphere carbon flux in sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) saplings

Despite its importance in the terrestrial C cycle rhizosphere carbon flux (RCF) has rarely been measured for intact root–soil systems. We measured RCF for 8‐year‐old saplings of sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) collected from the Hubbard Brook Experimental Forest (HBEF), NH and transplanted into pots with native soil horizons intact. Five saplings of each species were pulse labeled with ¹³CO₂ at ambient CO₂ concentrations for 4–6 h, and the ¹³C label was chased through rhizosphere and bulk soil pools in organic and mineral horizons for 7 days. We hypothesized yellow birch roots would supply more labile C to the rhizosphere than sugar maple roots based on the presumed greater C requirements of ectomycorrhizal roots. We observed appearance of the label in rhizosphere soil of both species within the first 24 h, and a striking difference between species in the timing of ¹³C release to soil. In sugar maple, peak concentration of the label appeared 1 day after labeling and declined over time whereas in birch the label increased in concentration over the 7‐day chase period. The sum of root and rhizomicrobial respiration in the pots was 19% and 26% of total soil respiration in sugar maple and yellow birch, respectively. Our estimate of the total amount of RCF released by roots was 6.9–7.1% of assimilated C in sugar maple and 11.2–13.0% of assimilated C in yellow birch. These fluxes extrapolate to 55–57 and 90–104 g C m^?2 yr^?1 from sugar maple and yellow birch roots, respectively. These results suggest RCF from both arbuscular mycorrhizal and ectomycorrhizal roots represents a substantial flux of C to soil in northern hardwood forests with important implications for soil microbial activity, nutrient availability and C storage.     

Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global-scale environmental change

Current ecosystem model predictions concerning the effects of global temperature increase on forest responses do not account for factors influencing long‐term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' ability to adapt to global‐scale environmental change without experiencing major alterations in current range limits. Genetic variation and structure in sugar maple (Acer saccharum Marsh.) were examined across three regions, between two stands within regions, and among four to five open‐pollinated families within stands (total N = 547 genotypes) using 58 randomly amplified polymorphic DNA (RAPD) markers. Differences within open‐pollinated families account for the largest portion of the total variation (29%), while differences among regions represent less than 2% of the total variation. Genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity (greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation among families indicate that vegetational models designed to predict species' response to global‐scale environmental change may need to consider the degree and hierarchical structure of genetic variation when making large‐scale inferences.     

The effect of crown architecture on dynamic amplification factor of an open-grown sugar maple (Acer saccharum L.)

Tree failure may cause significant economic and societal disruptions in urban environments. A better understanding of the relationship between branches and stem as they affect the dynamic response of decurrent trees under wind loading is needed to reduce the risk of tree failure. Finite element (FE) models were used to identify the parameters that primarily impact tree response. A base model was developed using data from a sugar maple (Acer saccharum L.) located in Belchertown, MA, USA, from which parametric models were subsequently developed. Confidence in the base model was gained by comparing the natural frequency of this tree with experimental results. Results from a parametric study incorporating changes in eight different tree parameters (stem diameter, slenderness ratio of branches, number of branches, damping ratio, branch attachment heights, branch attachment angles, branch azimuth angles, and elastic modulus) are then presented to help identify critical model properties that affect the dynamic amplification factor (Rd) of the tree. A single parameter was varied in each model while keeping others unchanged from the base model. Parameters with the greatest effect on Rd included stem diameter, number and slenderness of branches in the crown, elastic modulus of stem and branches, and damping ratio. Thus, it may be possible to use pruning to alter crown architecture to reduce the risk of tree failure.     

Sugar maple (Acer saccharum Marsh.) establishment in boreal forest: results of a transplantation experiment

Aim To evaluate whether seedlings of sugar maple (Acer saccharum Marsh.) can establish beyond the species northern range limit in adjacent boreal forest. Location The hardwood–boreal forest transition zone on the north‐east shore of Lake Superior, Ontario, Canada. Methods Seed fall of sugar maple was monitored for 5 years in a stand of this species at its northern range limit, and seed from this stand was transplanted to five micro‐habitat types in an adjacent boreal forest. The establishment and survival of sugar maple seedlings there, and in the seed‐source stand, was monitored for the following 7–11 years. Soil‐surface light levels were measured in both forest types. Results Most seed fell in the final year of monitoring, when c. 250 seeds m^?2 were recorded. First‐year seedling establishment rates in the maple stand, deriving from this mast seed year, was approximately double that deriving from seed transplanted to the boreal forest sites; this is tentatively attributed to seed predator satiation in the maple stand. However, subsequent seedling survivorship in the boreal forest was greater than that in the maple stand, resulting in comparable seedling densities by the end of 6 years. This difference is tentatively attributed to better illumination in the boreal forest sites, and canopy‐opening disturbances appear to be especially facilitative of seedling survival. Main conclusions There is no fundamental impediment to sugar maple seedlings establishing in boreal forest communities if climate warming occurs and seed is available. If management intervention is needed to accelerate seed availability in a rapidly warming boreal forest, then diffuse seed application to disturbed boreal forest sites during mast years of local boreal tree species is recommended as the most effective way of avoiding seed predation and increasing seedling survival.     

Cryopreservation of Steinernema carpocapsae and Heterorhabditis bacteriophora

A method for the cryopreservation of third-stage infective juveniles (IJ) of Steinernema carpocapsae and Heterorhabiditis bacteriophora was developed. Cryoprotection was achieved by incubating the nematodes in 22% glycerol (S. carpocapsae) or 14% glycerol (H. bacteriophora) for 24 hours, followed by 70% methanol at 0 C for 10 minutes. The viability of S. carpocapsae frozen in liquid nitrogen as 20 μl volumes spread over cover slip glass was > 80%. Survival of H. bacteriophora frozen on glass varied from 10 to 60% but was improved to > 80% by replacing the glass with filter paper. Cryopreservation and storage of 1-ml aliqots of S. carpocapsae IJ resulted in > 50% survival after 8 months; pathogenicity was retained and normal in vitro development took place. Trehalose and glycerol levels increased and glycogen levels decreased during incubation of S. carpocapsae IJ in glycerol. Normal levels of trehalose, glycerol and glycogen were restored during post freezing rehydration.     

Effects of base cation fertilization on the nutrient status,free amino acids and some carbon fractions of the leaves of sugar maple (Acer saccharum Marsh.)

A study was conducted in the Lower Laurentians of southern Quebec to test the hypothesis that base cation fertilization would improve the nutrient status of declining sugar maples (Acer saccharum Marsh.) and alter the partitioning of leaf C and N. Six 40×40 m plots were delineated in an 80 year old stand of sugar maple. Three plots received a mixture of fertilizer and liming materials (500 kg ha^–1 of K₂SO₄, 250 kg ha^–1 of CaCO₃ and 250 kg ha^–1 of CaMg(CO₂)₂) in the spring of 1989. Leaves from mid crown of dominant or co-dominant maples were sampled monthly during the 1990 growing season. Trees were cored in 1992 to measure their response in diameter growth. Fertilization increased diameter growth and foliar K concentration of trees but reduced foliar Ca concentration. Fertilization resulted in lower starch concentrations and higher ratios of soluble sugars to starch in June and September, and in higher free amino acid concentrations but lower ratio of total non-structural carbohydrates to free amino acids in September. Leaf proline concentration was correlated with leaf starch concentration (r=0.39). The results suggest that amelioration of K deficiencies in sugar maple through fertilization with a mixture of base cations can increase tree growth and affect the seasonal dynamics of foliar C and N pools.Abbreviations FAA free amino acids - TNC total non-structural carbohydrates     

Diet Composition and Lipids of In Vitro-Produced Heterorhabditis bacteriophora

Several entomopathogenic nematode species are currently under evaluation for mass production and field efficacy for biological control of insect pests. However, quality and quantity of in vitro-produced entomopathogenic nematodes vary considerably, depending on media, temperature, and production method. In addition, nematode production should be cost effective. We investigated nematode yield, production time, total lipid content, and fatty acid composition of Heterorhabditis bacteriophora produced in artificial media supplemented with different lipid sources. Lipid source significantly affected lipid quantity and quality in H. bacteriophora. Media supplemented with extractable insect lipids produced yields 1.9 times higher than did beef fat- or lard-supplemented media. Moreover, the developmental rate in media supplemented with host lipids was 1.7 times faster than that in media supplemented with beef fat or lard. Nematodes grown in media supplemented with insect lipids accumulated significantly higher lipid proportion per dry biomass than those grown in media supplemented with other lipid sources. H. bacteriophora produced in media supplemented with insect lipids, olive oil, or canola oil had similar fatty acid patterns, with oleic (18:1) acid as the major lipid fatty acid. Media supplemented with other lipid sources produced nematodes with fatty acid patterns different from those of media supplemented with insect lipids. We recommend addition of fatty acid mixtures that resemble natural host lipids for mass-producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes and could improve yield.