Effects of elevated atmospheric CO2 and/or O3 on intra- and interspecific competitive ability of aspen

Three model communities of trembling aspen (monoculture, and mixed with either paper birch or sugar maple) were grown for seven years in elevated atmospheric CO(2) and O(3) using Free Air CO(2) Enrichment (FACE) technology. We utilized trends in species' importance, calculated as an index of volume growth and survival, as indications of shifting community composition. For the pure aspen communities, different clones emerged as having the highest change in relative importance values depending on the pollutant exposure. In the control and elevated CO(2) treatments, clone 42E was rapidly becoming the most successful clone while under elevated O(3), clone 8 L emerged as the dominant clone. In fact, growth of clone 8 L was greater in the elevated O(3) treatment compared to controls. For the mixed aspen-birch community, importance of aspen and birch changed by - 16 % and + 62 %, respectively, in the controls. In the treatments, however, importance of aspen and birch changed by - 27 % and + 87 %, respectively, in elevated O(3), and by - 10 % and + 45 %, respectively, in elevated CO(2). Thus, the presence of elevated O(3) hastened conversion of stands to paper birch, whereas the presence of elevated CO(2) delayed it. Relative importance of aspen and maple changed by - 2 % and + 3 %, respectively, after seven years in the control treatments. But in elevated O(3), relative importance of aspen and maple changed by - 2 % and + 5 %, respectively, and in elevated CO(2) by + 9 and - 20 %, respectively. Thus, elevated O(3) slightly increases the rate of conversion of aspen stands to sugar maple, but maple is placed at a competitive disadvantage to aspen under elevated CO(2).     

SEASONAL AND INDIVIDUAL VARIATION IN LEAF QUALITY OF TWO NORTHERN HARDWOODS TREE SPECIES

Seasonal trends in five traits of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula allegheniensis Britt.) leaves thought to influence feeding by herbivores were measured from 17 May through 19 September, 1979. Total nitrogen and water contents declined and toughness increased through the growth season. These seasonal changes were more pronounced in sugar maple than in yellow birch. Total polyphenol contents and tanning coefficients of leaf extracts from both species reached a season high by the end of May and changed very little after that date; these patterns differ from those reported by several other investigators. Sugar maple leaf extracts exhibited much higher tanning coefficients than did those of yellow birch, a finding which is consistent with current plant defense theory. Significant differences in total polyphenol content and tanning coefficients were found between individual trees in yellow birch, but not sugar maple. The relationship between successional status, leaf quality traits, and variability in these traits in forest trees is discussed.     

Effects of CO2 and light on tree phytochemistry and insect performance

Direct and interactive effects of CO₂ and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acer saccharum) were grown under ambient (387±8 μL/L) and elevated (696±2 μL/L) levels of atmospheric CO₂, with low and high light availability (375 and 855 μmol×m^?2×s^?1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white‐marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short‐term (fourth instar) feeding trials were conducted with insects fed detached leaves.
Phytochemical analyses demonstrated strong effects of both CO₂ and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO₂ decreased water content and increased starch content, especially under high light conditions. High CO₂ availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO₂ and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO₂, respectively.
The long‐term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general, CO₂ effects were pronounced in high light and decreased along the gradient aspen birch maple. For larvae reared on high light aspen, enriched CO₂ resulted in 62% fewer survivors, with increased development time, and reduced pupal mass. For maple‐fed insects, elevated CO₂ levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO₂ effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO₂ significantly reduced total consumption, especially by insects on high light aspen and low light maple.
This research demonstrates that effects of CO₂ on phytochemistry and insect performance can be strongly light‐dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO₂ availability appeared to increase the defensive capacity of early‐successional species primarily under high light conditions, and of late‐successional species under low light conditions. Due to the interactive effects of tree species, light, CO₂, and herbivory, community composition of forests may change in the future.     

Hierarchical structure of juvenile hybrid aspen xylem revealed using X-ray scattering and microtomography

X-ray scattering and microtomography (μCT) are useful techniques to reveal the structure of wood at the nano- and micrometer scales. The nanostructure of xylem in greenhouse-grown 2.5- to 3.5-month-old Populus tremula L.?×?tremuloides Michx. trees was characterized using wide-angle X-ray scattering (WAXS), and the cellular structure was investigated using μCT. For comparison, the nanostructure of wood in 2-year-old silver birch, Norway spruce and Scots pine saplings was determined. Based on the μCT results, the lengths of fiber lumina of the hybrid aspen saplings were shorter than any previous results on the lengths of wood fibers. The mean microfibril angles of the hybrid aspen saplings were significantly lower (8°–14°) than those of the birch, spruce and pine saplings (27°–35°) implicating that cellulose microfibrils were oriented nearly parallel to the cell axis in the young hybrid aspen saplings. Hybrid aspen saplings were found to contain tension wood based on the histochemical analysis and μCT images. However, typical tension wood properties, i.e. larger crystallite width and higher crystallinity than in normal wood, were detected only in a few hybrid aspen samples, while in most of the hybrid aspen saplings, the crystallite widths (3.0?±?0.1?nm) and the crystallinities (30?±?5?%) corresponded to those of normal wood. The deformations of cellulose crystallites were determined using WAXS in situ upon dehydration of the never-dried samples. In all the species studied, the cellulose unit cell dimension decreased and disorder of cellulose chains increased parallel to the chains upon drying. Also, the transverse disorder of chains increased in birch, spruce and pine, while no changes were detected in this direction in hybrid aspen. The crystallite widths and drying deformation results might indicate that the gelatinous layer has not fully developed in the young hybrid aspen saplings.     

TEMPORAL AND SPATIAL PATTERNS OF SPECIFIC LEAF WEIGHT IN SUCCESSIONAL NORTHERN HARDWOOD TREE SPECIES

Temporal and spatial patterns of specific leaf weight (SLW, g/m²) were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan to evaluate the utility of SLW as an index of leaf photosynthetic capacity. No significant diurnal changes in SLW were found. Specific leaf weight decreased and then increased during leaf expansion in the spring. Most species, especially those located in the understory, then had relatively constant SLW for most of the growing season, followed by a decline in SLW during autumn. Specific leaf weight decreased exponentially down through the canopy with increasing cumulative leaf area index. Red oak (Quercus rubra), paper birch (Betula papyrifera), bigtooth aspen (Populus grandidentata), red maple (Acer rubrum), sugar maple (A. saccharum), and beech (Fagus grandifolia) generally had successively lower SLW, for leaves at any one level in the canopy. On a given site, comparisons between years and comparisons of leaves growing within 35 cm of each other showed that differences in SLW among species were not due solely to microenvironmental effects on SLW. Bigtooth aspen, red oak, and red maple on lower-fertility sites had lower SLW than the same species on higher-fertility sites. Maximum CO₂ exchange rate, measured at light-saturation in ambient CO₂ and leaf temperatures of 20 to 25 C, increased with SLW. Photosynthetic capacities of species ranked by SLW in a shaded habitat suggest that red oak, red maple, sugar maple, and beech are successively better adapted to shady conditions.     

Differential drought responses between saplings and adult trees in four co-occurring species of New England

Tree-ring characteristics in four species were examined to address whether co-occurring mature trees of different successional status respond differently to drought, and whether saplings of these species have a greater response to drought than mature trees. We examined saplings and mature trees of paper birch, yellow birch, red maple and sugar maple, which varied in successional status (shade-tolerance) and co-occurred at Harvard Forest, Petersham, Mass., USA. Three drought events in 1964–1966, 1981 and 1995 were identified using climate data. For mature trees, there was no significant interspecific difference in relative changes in ring-width index (RWI) during the 1964–1966 and 1995 drought events. However, the interspecific difference was significant in the 1981 drought event. Response function analysis for mature trees showed that the radial growth of sugar maple was mainly controlled by spring and summer precipitation, red maple by spring and summer precipitation and temperature, yellow birch by winter and summer precipitation, and spring and summer temperature, and paper birch by spring and summer precipitation and spring temperature. Saplings of sugar maple and yellow birch, but not red maple and paper birch, showed significant positive correlations between RWI and annual total precipitation. In the 1995 drought event, saplings and mature trees of red maple and paper birch differed significantly in drought responses, but this was not true in sugar maple and yellow birch. Our results do not support a generally greater response in saplings than in mature trees, nor an early- versus late successional difference in drought responses.     

Elevated CO2 differentially alters the responses of coocurring birch and maple seedlings to a moisture gradient

Summary To determine the effects of elevated CO₂ and soil moisture status on growth and niche characteristics of birch and maple seedlings, gray birch (Betula populifolia) and red maple (Acer rubrum) were experimentally raised along a soil moisture gradient ranging from extreme drought to flooded conditions at both ambient and elevated atmospheric CO₂ levels. The magnitude of growth enhancement due to CO₂ was largely contingent on soil moisture conditions, but differently so for maple than for birch seedlings. Red maple showed greatest CO₂ enhancements under moderately moist soil conditions, whereas gray birch showed greatest enhancements under moderately dry soil conditions. Additionally, CO₂ had a relatively greater ameliorating effect in flooded conditions for red maple than for gray birch, whereas the reverse pattern was true for these species under extreme drought conditions. For both species, elevated CO₂ resulted in a reduction in niche breadths on the moisture gradient; 5% for gray birch and 23% for red maple. Species niche overlap (proportional overall) was also lower at elevated CO₂ (0.98 to: 0.88: 11%). This study highlights the utility of of experiments crossing CO₂ levels with gradients of other resources as effective tools for elucidating the potential consequences of elevated CO₂ on species distributions and potential interactions in natural communities.     

Isolation and characterization of O-acetylated glucomannans from aspen and birch wood

O-acetylated glucomannans were isolated from aspen and birch wood employing two different procedures and thereafter subjected to carbohydrate analysis by NMR spectroscopy and MALDI mass spectrometry. In one of the isolation procedures, acetone-extracted aspen or birch wood meal was extracted with dimethyl sulfoxide and then with hot water. Fractionation of the hemicellulose-containing extracts by size-exclusion chromatography was subsequently performed. In the other procedure, fractional precipitation with ethanol was used to isolate glucomannans from lyophilized process water produced by mechanical pulping of aspen. The aspen and birch glucomannans are O-acetylated at the C-2 or C-3 position of some of the mannose residues (random distribution), with a degree of acetylation of approx 0.3. In both cases the degree of polymerization was approx 16, indicating that low-molecular mass fractions of the glucomannans in hardwood have been isolated here.     

Cutting xylem under tension or supersaturated with gas can generate PLC and the appearance of rapid recovery from embolism

We investigated the common assumption that severing stems and petioles under water preserves the hydraulic continuity in the xylem conduits opened by the cut when the xylem is under tension. In red maple and white ash, higher percent loss of conductivity (PLC) in the afternoon occurred when the measurement segment was excised under water at native xylem tensions, but not when xylem tensions were relaxed prior to sample excision. Bench drying vulnerability curves in which measurement samples were excised at native versus relaxed tensions showed a dramatic effect of cutting under tension in red maple, a moderate effect in sugar maple, and no effect in paper birch. We also found that air injection of cut branches (red and sugar maple) at pressures of 0.1 and 1.0 MPa resulted in PLC greater than predicted from vulnerability curves for samples cut 2 min after depressurization, with PLC returning to expected levels for samples cut after 75 min. These results suggest that sampling methods can generate PLC patterns indicative of repair under tension by inducing a degree of embolism that is itself a function of xylem tensions or supersaturation of dissolved gases (air injection) at the moment of sample excision. Implications for assessing vulnerability to cavitation and levels of embolism under field conditions are discussed.     

Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species

• 1 Natural forest systems constitute a major portion of the world's land area, and are subject to the potentially negative effects of both global climate change and invasion by exotic insects. A suite of invasive weevils has become established in the northern hardwood forests of North America. How these insects will respond to increasing CO₂ or O₃ is unknown.
• 2 The present study examined the effects of elevated atmospheric CO₂ and O₃ on the invasive weevil Polydrusus sericeus Schaller at the Aspen Free Air CO₂ Enrichment (FACE) site near Rhinelander, Wisconsin. A performance assay was conducted in the laboratory during the summer of 2007 using mated pairs of P. sericeus fed a combination of aspen, birch and maple foliage. We recorded leaf area consumption, oviposition and adult longevity. We also conducted visual abundance surveys in the field from 2004 to 2007 on aspen and birch at Aspen FACE.
• 3 Elevated CO₂, but not O₃, significantly affected P. sericeus performance. Female, but not male, longevity was reduced under elevated CO₂. Polydrusus sericeus also produced fewer eggs under elevated CO₂ conditions compared with ambient conditions. Adult P. sericeus strongly preferred birch over both aspen and maple, regardless of fumigation treatment.
• 4 The effects of elevated CO₂ on P. sericeus populations at Aspen FACE were minimal, and varied among years and host tree species. Polydrusus sericeus abundance was significantly greater on birch than aspen. Over the long term, elevated CO₂ may reduce adult female longevity and fecundity of P. sericeus. Further studies are needed to evaluate how this information may scale to ecosystem impacts.

     

Palatability of transgenic birch and aspen to roe deer and mountain hare

Genetic engineering of plant resistance characteristics against fungi may unintentionally influence traits that are important for plant–herbivore interactions. We studied the palatability of transgenic birch (Betula pendula), aspen (Populus tremula) and hybrid aspen (P. tremula x tremuloides) genetically modified with the aim to improve fungal disease resistance, to selective mammalian herbivores in cafeteria tests. Roe deer (Capreolus capreolus) were fed with transgenic birch carrying a sugar beet chitinase IV gene. In the experiment with roe deer, none of the six transgenic birch lines differed significantly from the wild-type control in the proportion of consumed plant biomass. Correlation analyses suggested that sugar content did not guide the feeding preferences of roe deer but revealed a positive correlation between starch content and proportion of mass consumed. However, the variation in starch content could not be related to the level of transgene expression. Mountain hares (Lepus timidus) were fed with plant material from chitinase transgenic birch and aspen and hybrid aspen that carried a pinosylvin synthase gene from Scots pine. One transgenic birch line was significantly less palatable to hares than the wild-type control. The results of this study suggest that plant genotype may be related to the palatability of plant material when transgenic and wild-type woody plant material is used as winter food for hares. The results of this case study did not reveal changes in the palatability of the studied transgenic lines that could be readily related to the functioning of the used transgenes.     

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.     

Impact of drying and re-wetting on N,P and K dynamics in a wetland soil

As increased nutrient availability due to drainage is considered a major cause of eutrophication in wetlands rewetting of drained wetlands is recommended as a restoration measure. The effect of soil drying and rewetting on the contribution of various nutrient release or transformation processes to changed nutrient availability for plants is however weakly understood. We measured effects of soil drying and re-wetting on N mineralization, and denitrification, as well as on release of dissolved organic nitrogen (DON), phosphorus, and potassium in incubated soil cores from a wet meadow in southern Sweden. Additionally, the impact of re-wetting with sulphate-enriched water was studied. Soil drying stimulated N mineralization (3 times higher) and reduced denitrification (5 times lower) compared to continuously wet soil. In the wet cores, denitrification increased to 20 mg N m^–2 d^–1, which was much higher than denitrification measured in the field. In the field, increased inorganic-N availability for plants due to drainage seemed primarily to be caused by increased N mineralization, and less by decreased denitrification. Soil drying also stimulated the release of DON and K, but P release was not affected. Re-wetting of dried soil cores strongly stimulated denitrification (up to 160 mg N m^–2 d^–1), but N mineralization was not significantly decreased, neither were DON or K release. In contrast, the extractable P pool increased upon soil wetting. Re-wetting with sulphate-enriched water had no effect on any of the nutrient release or transformation rates. We conclude that caution is required in re-wetting of drained wetlands, because it may unintendently cause internal eutrophication through an increased P availability for plants.     

Enriched atmospheric CO2 and defoliation: effects on tree chemistry and insect performance

We examined the effects of CO₂ and defoliation on tree chemistry and performance of the forest tent caterpillar, Malacosoma disstria. Quaking aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees were grown in open-top chambers under ambient or elevated concentrations of CO₂. During the second year of growth, half of the trees were exposed to free-feeding forest tent caterpillars, while the remaining trees served as nondefoliated controls. Foliage was collected weekly for phytochemical analysis. Insect performance was evaluated on foliage from each of the treatments. At the sampling date coincident with insect bioassays, levels of foliar nitrogen and starch were lower and higher, respectively, in high CO₂ foliage, and this trend persisted throughout the study. CO₂-mediated increases in secondary compounds were observed for condensed tannins in aspen and gallotannins in maple. Defoliation reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. Similarly, defoliation induced accumulations of secondary compounds in aspen but not in maple. Larvae fed foliage from the enriched CO₂ or defoliated treatments exhibited reduced growth and food processing efficiencies, relative to larvae on ambient CO₂ or nondefoliated diets, but the patterns were host species-specific. Overall, CO₂ and defoliation appeared to exert independent effects on foliar chemistry and forest tent caterpillar performance.     

Scaling ozone responses of forest trees to the ecosystem level in a changing climate

Many uncertainties remain regarding how climate change will alter the structure and function of forest ecosystems. At the Aspen FACE experiment in northern Wisconsin, we are attempting to understand how an aspen/birch/maple forest ecosystem responds to long-term exposure to elevated carbon dioxide (CO₂) and ozone (O₃), alone and in combination, from establishment onward. We examine how O₃ affects the flow of carbon through the ecosystem from the leaf level through to the roots and into the soil micro-organisms in present and future atmospheric CO₂ conditions. We provide evidence of adverse effects of O₃, with or without co-occurring elevated CO₂, that cascade through the entire ecosystem impacting complex trophic interactions and food webs on all three species in the study: trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh), and sugar maple (Acer saccharum Marsh). Interestingly, the negative effect of O₃ on the growth of sugar maple did not become evident until 3 years into the study. The negative effect of O₃ effect was most noticeable on paper birch trees growing under elevated CO₂. Our results demonstrate the importance of long-term studies to detect subtle effects of atmospheric change and of the need for studies of interacting stresses whose responses could not be predicted by studies of single factors. In biologically complex forest ecosystems, effects at one scale can be very different from those at another scale. For scaling purposes, then, linking process with canopy level models is essential if O₃ impacts are to be accurately predicted. Finally, we describe how outputs from our long-term multispecies Aspen FACE experiment are being used to develop simple, coupled models to estimate productivity gain/loss from changing O₃.     

Leaf litter quality and decomposition rates of yellow birch and sugar maple seedlings grown in mono-culture and mixed-culture pots at three soil fertility levels

Seedlings of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh.) were grown for 2 years in mono-culture and mixed-culture and at three fertility levels. Following the second growing season, senescent leaves were analysed for N concentration, acid hydrolysable substances (AHS), and nonhydrolysable remains (NHR). A litter sub-sample was then inoculated with indigenous soil microflora, incubated 14 weeks, and mass loss was measured. Litter-N was significantly higher at medium than at poor fertility, as well as in yellow birch than in sugar maple litter. The species effect on litter-N increased with increasing fertility. At medium fertility, litter-N of sugar maple litter was lower in mixed-culture than in mono-culture. AHS, NHR as well the NHR/N ratio were significantly higher in yellow birch than in sugar maple litter. At medium fertility, the NHR/N ratio of sugar maple litter was significantly lower in mono-culture than in mixed-culture. Mass loss was significantly greater at medium and rich fertility than at poor fertility, and in yellow birch than in sugar maple litter. At poor fertility, mixed-litter decomposed at a rate comparable to yellow birch, whereas at medium and rich fertility, mixed-litter decomposed at a rate comparable to sugar maple. There was a significant positive relationship between litter-N and mass loss. A similar positive relationship between NHR and mass loss was presumed to be a species effect on decomposition. Results support the hypothesis that species × fertility and species × mixture interactions can be important determinants of litter quality and, by implication, of site nutrient cycling.     

Abscisic acid promotes root system development in birch tissue culture: a comparison to aspen culture and conventional rooting‐related growth regulators

The research aim was to assess the effects of the plant hormone abscisic acid (ABA) and the growth regulator paclobutrazol (PBZ) on root system development during the in vitro culture of different birch and aspen genotypes. The studied genotypes involved two aspen (Populus tremula and Populus tremuloides × P. tremula) and two silver birch (Betula pendula) trees, with one of the birches characterized by its inability to root in vitro. For experiments, apical shoot segments were cultured on nutrient medium enriched with either ABA or PBZ. Additionally, the analysis of the endogenous hormones in shoots developed on hormone‐free medium was conducted by high‐performance liquid chromatography. The endogenous concentration of auxin indole‐3‐acetic acid was much higher in the aspens than that in the birches, while the highest concentration of ABA was found in the root‐forming birch. The culturing of this birch genotype on medium enriched with ABA resulted in an increased root length and a higher number of lateral roots without any negative effect on either shoot growth or adventitious root (AR) formation, although these two processes were largely inhibited by ABA in the aspens. Meanwhile, PBZ promoted AR formation in both aspen and birch cultures but impaired secondary root formation and shoot growth in birches. These results suggest the use of ABA for the in vitro rooting of birches and PBZ for the rooting of aspens.     

Effects of 76 Hz electromagnetic fields on forest ecosystems in northern Michigan: Tree growth

Since 1984, the possible effects of extremely low-frequency electromagnetic (EM) fields generated by a 76 Hz communication antenna on the growth and productivity of four deciduous and one coniferous species have been studied in the Upper Peninsula of Michigan. Results from two research sites are discussed here: one site near an antenna element and a control site located 50 km from the communication system. Growth models for individual tree diameters were developed for northern red oak (Quercus rubra), paper birch (Betula papyrifera), aspen (Populus tremuloides with a few individuals ofP. grandidentata), and red maple (Acer rubrum). A growth model for individual tree height was developed for young red pine (Pinus resinosa). Average differences between the observed and predicted growth were calculated for each growing season and then compared between the study sites and across the study periods to evaluate changes in growth patterns which could be attributed to EM field effects. For aspen and red maple, the results showed a stimulation of diameter growth at magnetic flux density levels of 1 to 7 milliGauss; height growth of red pine was increased at about the same exposure levels. There are no clear indications of an EM field effect on total annual diameter growth for either of the other two species.     

Do enzymatic hydrolyzability and Simons' stain reflect the changes in the accessibility of lignocellulosic substrates to cellulase enzymes?

In an attempt to elucidate the impact of substrate accessibility to cellulases on the susceptibility of lignocellulosic substrates to enzymatic hydrolysis, a hydrogen peroxide treated, Douglas fir kraft pulp was dried using several methods with varying levels of intensity. Oven-drying at 50 and 100 degrees C, air-drying, and freeze-drying methods were employed to remove the interfibrillar water from the pulp samples. Subsequently, the never-dried and variably dried pulps were hydrolyzed using a commercial cellulase preparation supplemented with additional beta-glucosidase. Drying reduced the susceptibility of the substrates to enzymatic hydrolysis, which can be attributed to the hornifying effect that drying has on fibers. This effect was more pronounced for the fibers that were oven-dried at 100 degrees C (23% reduction) and 50 degrees C (15% reduction), and there was a good correlation between the Simons's stain results and the enzymatic digestibility of the dried pulps. These observations indicated that drying significantly reduced the population of larger pores and that the partial closure of larger pores created a large number of smaller pores that were not accessible to the displacement dye molecules (orange dye). The inaccessibility of the cellulose to the enzymes, due to the collapse or closure of the large pores, appears to be the primary reason for the lower susceptibility of the dried pulps to enzymatic hydrolysis.     

Stem wood properties of Populus tremuloides, Betula papyrifera and Acer saccharum saplings after 3 years of treatments to elevated carbon dioxide and ozone

The aim of this study was to examine the effects of elevated carbon dioxide [CO₂] and ozone [O₃] and their interaction on wood chemistry and anatomy of five clones of 3‐year‐old trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling‐origin saplings of the same age. Material for the study was collected from the Aspen Free‐Air CO₂ Enrichment (FACE) experiment in Rhinelander, WI, USA, where the saplings had been exposed to four treatments: control (C; ambient CO₂, ambient O₃), elevated CO₂ (560 ppm during daylight hours), elevated O₃ (1.5 × ambient during daylight hours) and their combination (CO₂+O₃) for three growing seasons (1998–2000). Wood chemistry responses to the elevated CO₂ and O₃ treatments differed between species. Aspen was most responsive, while maple was the least responsive of the three tree species. Aspen genotype affected the responses of wood chemistry and, to some extent, wood structure to the treatments. The lignin concentration increased under elevated O₃ in four clones of aspen and in birch. However, elevated CO₂ ameliorated the effect. In two aspen clones, nitrogen in wood samples decreased under combined exposure to CO₂ and O₃. Soluble sugar concentration in one aspen clone and starch concentration in two clones were increased by elevated CO₂. In aspen wood, α‐cellulose concentration changed under elevated CO₂, decreasing under ambient O₃ and slightly increasing under elevated O₃. Hemicellulose concentration in birch was decreased by elevated CO₂ and increased by elevated O₃. In aspen, elevated O₃ induced statistically significant reductions in distance from the pith to the bark and vessel lumen diameter, as well as increased wall thickness and wall percentage, and in one clone, decreased fibre lumen diameter. Our results show that juvenile wood properties of broadleaves, depending on species and genotype, were altered by atmospheric gas concentrations predicted for the year 2050 and that CO₂ ameliorates some adverse effects of elevated O₃ on wood chemistry.