Foliar sensitivity of eight eastern hardwood tree species to ozone

As part of a larger 3-yr study, container-grown seedlings of black cherry (Prunus serotina) red maple (Acer rubrum), red oak (Ouercus rubra), sweetgum (Liquidambar styraciflua), white ash (Fraxinus americana), white oak (Ouercus alba), yellow-poplar (Liriodendron tulipifera), and yellow birch (Betula allegheniensis) were exposed to 0,0.075, or 0.15 μL L-¹ O₃ in laboratory controlled-environment chambers for 6 hr d^?1 on 2 consecutive days for 12 weeks. On the third consecutive day of each week, plants were treated for 45 min with precipitation at pH 3.0 or 4.2. The only significant foliar symptoms were induced by the O₃ treatments, and the severity of symptoms was not influenced by precipitation pH. The most common symptom was a dark, adaxial stipple which was most severe on the oldest leaves. Equations were developed to express the influence of leaf position on percent leaf injury following 4, 8, and 12 weeks of treatment. Based on percent leaf tissue showing stipple and defoliation following exposure to 0.15 μL L^?1 O₃, the most sensitive species to O₃ was black cherry, followed by sweetgum, yellow-poplar, white ash, red maple and yellow birch. Red oak and white oak foliage did not exhibit stipple.     

Elemental analyses and physiological responses of forest trees in SO2-polluted areas of NE-Bavaria

Many areas of NE-Bavarian Mountains experience relatively high SO₂ concentrations (between 60 and 1400 μg m^?3). Since 1980,Picea abies, Abies alba, andLarix decidua have exhibited needle tipchlorosis and necrosis. Affected trees usually occur on acid soils above 700 m. Needles of affected trees ofP. abies had ample N, P concentrations. However, needle concentrations of Mg were very low, those of Ca, K, Zn of affected trees were relatively low. Although Al, Fe, and Cu concentrations were in the normal range, usually S concentrations were above the toxicity threshold. In the same region low concentrations of Mg were present in foliage ofAbies alba, Larix decidua, Fagus sylvatica, andAcer platanoides that exhibited visible leaf injury. Although some slight changes in water relations occurred, the present evidence suggests that Mg — deficiency may result from acid deposition and that this mineral deficiency may be responsible for tree injury.     

Gaseous Elemental Mercury Fluxes in New York City

As with many urban environments, a number of sources of airborne elemental mercury (Hg°) exist in New York City, yet little research has been conducted to examine the flux and sources of mercury in New York. In this study, we conducted ambient monitoring of Hg° at six locations in New York City. Airborne Hg° averaged 3.84±0.10 ng m^-3 and 3.70±0.08 ng m^-3 in the boroughs of Manhattan and Brooklyn respectively, yet only 2.69±0.03 ng m^-3 in a more residential neighborhood in Queens. Both precipitation and ambient temperature were significantly correlated with ambient Hg° levels in New York City, suggesting that the surface emission of mercury from urban surfaces plays a role in urban Hg° concentrations. Local sources were also seen to contribute to urban Hg° levels by leading to `spikes' of Hg° in which elevated concentrations were recorded for short periods of time.     

Modelization of the mercury fluxes at the air-sea interface

Aqueous and atmospheric Hg° concentrations for remote marine areas such as the equatorial Pacific Ocean and for coastal seas such as the North Sea and the Scheldt Estuary are discussed. Biological processes seem to be at the origin of the supersaturated Hg° concentrations in the water. On the other hand, transfer velocities across the air-sea interface were calculated with a classical shear turbulence model and with a wave breaking model. With these data, Hg° fluxes from the sea to the atmosphere were calculated: in the Pacific Ocean they range from 0.43 to 6.5 μg g Hg.m^?2. yr^?1 at a wind speed of 2.8 m.s^?1 and from 10.3 to 156 μg Hg.m^?2 yr^?1 at a wind speed of 54 m.s^?1, but they are still higher when wave breaking is considered (from 11 to 168 μg Hg.m^?2.yr^?1). These transfer fluxes are an order of magnitude higher in the Scheldt Estuary.     

Uptake of fluoride and aluminum by plants grown in contaminated soils

Soils collected from areas at different distances from an aluminum smelter were studied to determine the soluble and labile F and soluble Al contents and availabilities to selected plants. Red maple seedlings (Acer rubrum L.) and orchard grass (Dactylis glomerata L.) were grown in pots containing the soils and after 3 mo foliar tissues were sampled and analyzed for the two elements. The soluble and labile contents of soil F as predictors of foliar F were compared. Significant decreases in soluble and labile F and soluble Al in soils were found with increasing distance from the smelter. As F levels in the soils increased, the F in the foliage of both orchard grass and maple increased. As Al in the soil increased, Al in maple foliage increased. Overall, F concentrations in plant foliage were below those considered as background. The results imply that, at least in the soils studied, the soil F content is not an important source of F to plants and therefore to herbivores in the area. Labile F values in the soils were significantly greater than soluble F at all sites, but, contrary to previous studies, soluble F was a better predictor of foliar F than was labile F.     

Modeling the elemental mercury cycle in Pallette Lake,Wisconsin, USA

The spatial and temporal distribution of elemental Hg (Hg°) and reactive Hg (Hg_R) has been studied on Pallette Lake, Wisconsin during May – August, 1993 and May, 1994. In general, Hg° concentrations near the lake surface greatly exceeded saturation with respect to atmospheric Hg° indicating a flux out (?) of the lake. Evasional losses were estimated using a thin film model and averaged ?101 pmol m^?2 d^?1 during July and August, 1993. A large portion of atmospherically deposited Hg is re-emitted. Thus, in-lake Hg° production' and evasion to the atmosphere will significantly reduce the amount of Hg which is transported to the sediments, the principal site of methylation. Laboratory experiments were conducted to ascertain the rate of Hg° formation from Hg(II). Reduction was significantly lower in heat sterilized lakewater suggesting Hg° production was biologically mediated. The temporal distribution of epilimnetic Hg°, as measured at the lake center, was influenced by Hg° evasion, Hg° production and advective transport of water parcels of differing Hg content. Spatial gradients in Hg° and Hg_R were identified and a transport model was employed to estimate the advective flux of Hg°. The importance of atmospheric deposition and sediment-water interaction as sources of Hg_R to epilimnetic waters were examined. Porewater concentrations of Hg° and Hg_R were determined on several occasions. During May, 1994, the depletion of lakewater Hg_R following a input pulse due to rain was observed and the estimated removal rate (16–20% d^?1) agrees well with reduction rates obtained in the laboratory (23% d^?1).     

Nitrogen mineralization in boreal forest stands of isle royale,Northern Michigan

The correlation of soil temperature and moisture with inorganic N concentrations and net mineralization beneath major species types in mature boreal and northern hardwood forests was examined over a two year period. Soils beneath species types where the canopy was dominated byBetula papyrifera, Picea glauca, Alnus rugosa or, in northern hardwoods,Acer saccharum were studied. Net NO₃ ^? mineralization varied by species type and net total inorganic nitrogen (N) mineralization varied by month and the interaction of species type with month. Soil NO₃ ^? concentration and NO₃ ^? mineralization were correlated for spruce, and inversely correlated for alder and maple. Soil NH₄ ⁺ concentration and NH₄ ⁺ mineralization were inversely correlated for alder and maple. In laboratory temperature and moisture treatments of birch, spruce and maple soils, NH₄ ⁺ and total inorganic N-mineralization increased with temperature. The response to moisture was most evident for NO₃ ^? mineralization in maple soils.     

Temperature effects on plant response to sulfur dioxide in Zea mays,Liriodendron tulipifera,and Fraxinus pennsylyanica

The influence of a 7 °C range of air temperature (28 to 35 °C) on plant response to SO₂ (0.4 μL L^?1 for 7 hr) was investigated in herbaceous (Zea mays) and woody (Liriodendron tulipifera and Fraxinus pennsylvanica) species. The indices of plant response were SO₂-induced changes in photosynthesis and the transpiration ratio. The physiological basis of differences in response as a function of temperature was evaluated through determination of SO₂ flux to foliage. The most consistent influence of the higher temperature for all three species was an increase of 20 to 50% in the foliar S content. The transpiration ratio and photosynthesis were more responsive to SO₂ at the higher temperature in both woody species but less responsive in Z. mays. Thus, the pattern of SO₂-induced injury as a function of temperature was not consistent among all species. Several mechanisms are proposed to account for the increase in SO₂ flux at higher temperatures, including a change in stomatal conductance and direct temperature effects on the conductivity of the diffusive media (gas and liquid phase) and the kinetic energy of SO₂ molecules. Since the pattern of temperature-dependent plant responses to SO₂ was species-specific, generalizations about the modifying role of temperature on plant responses to SO₂ are limited.     

Particle-size distribution of PAH in the air of a remote Norway spruce forest in northern Bavaria

The aim of the present study was to elucidate thedistribution of particulate polycyclic aromatichydrocarbons (PAH) in the air of a remote Norwayspruce (Picea abies (L.) karst.) stand.The study encompassed a total of twenty differentcongeners. Particles in ambient air were alternativelycollected by two different Berner cascade impactors atthe field site in Northern Bavaria over a 14-weeksperiod from the end of April through to the end ofJuly 1994 and subsequently analyzed for their PAHcontent. The concentrations of total suspendedparticulate matter (TSP) ranged from 9–31 μg m^-3,suggesting that the field site is an area with a lowlevel of airborne particles. There was a negativerelationship of total particle concentrations with theamount of canopy precipitation due to particle washout at precipitation events. The distribution of theparticle masses on the different size fractions witha maximum in the 1-μm range is typical for remoteareas and indicates a medium-range transport. Theaerosol-bound PAH load decreased from spring sampleswith 2–4 ng m^-3 to values <1 ng m^-3 in the summersamples. Concurrently, the proportion of low molecularweight congeners in the total PAH load declined.Frequently, the highest PAH concentrations (referringto the air) were found in the 0.1–3 μm sizeseparates (accumulation mode). The results suggestthat apart from PAH input to the soil with litter, dryand wet deposition of aerosol particles is animportant pathway of PAH contamination of acid forestsoils in the Fichtelgebirge mountain range.     

Response of three eastern tree species to supplemental UV-B radiation: leaf chemistry and gas exchange

Quantitative changes in foliar chemistry in response to UV-B radiation are frequently reported but less is known about the qualitative changes in putative UV-screening compounds. It has also not been conclusively shown whether qualitative differences in screening compounds or differences in localization patterns influence the sensitivity of plants to damage from UV-B radiation and there is some question as to whether differences in the amounts of soluble screening compounds correlate with physiological sensitivity to UV-B radiation. This study represents the first part of a multiple-year study designed to answer the above questions. In this study we evaluated whether differences in soluble UV-screening compounds were linked with possible effects on gas exchange and photosynthetic carbon assimilation. Branches of mature trees of sweet gum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were exposed to supplemental levels of UV-B radiation over three growing seasons. Controls for UV-A were also measured by exposing branches to supplemental UV-A only and additional branches not irradiated were also used for controls. These species demonstrated differing levels of screening compounds with poplar being the most responsive in terms of epidermal accumulation of phenolics. These were separately identified as flavonols, chlorogenic acid and hydroxycinnamates (HCAs). Red maple had the highest levels of constitutive UV-absorbing compounds but these showed little response to supplemental UV-B radiation. Leaf area was marginally influenced by UV exposure level with both UV-A and UV-B tending to reduce leaf area in red maple and poplar and increase it in sweet gum, when averaged over the 3-year period. Assimilation was generally not reduced by UV-B radiation in these species and was enhanced in red maple by both UV-B and UV-A and by UV-A in sweet gum. These findings are consistent with a hypothesis that epidermal attenuation of UV-B would only be reduced in poplar, which accumulated the additional epidermal screening compounds. It is possible that photosynthetic efficiency was enhanced in red maple by the increased absorption of blue light within the mesophyll due to elevated levels of HCAs. Stomatal conductance was generally reduced and this led to an increase in water use efficiency (WUE) in red maple and poplar. Since few detrimental effects of supplemental UV-B were observed, these results suggest that these tree species utilized a range of UV-screening compounds and deposition patterns to achieve UV-B tolerance and further, that subtle responses to UV-B could have ecological significance in the absence of reduced productivity or photosynthetic efficiency.     

The short-term effects of wood-ash amendment on forest soils

In the heavily forested regions of the northeastern U.S. the potential for producing electricity from wood-fired boilers is also creating a growing supply of wood-ash requiring disposal. Landfill space is expensive and limited, which has resulted in an interest in spreading wood-ash on forest sites. This greenhouse study was designed to provide information on soil and seedling response to wood-ash applications. Red maple (Acer rubrum) seedlings were grown in either O or B horizon forest soil material and amended with six levels of ash (0, 4, 8, 12, 16, and 20 Mg ha^?1) and two levels of N fertilizer (0 and 224 kg ha^?1). Ash amendments increased pH and exchangeable base cations, and decreased extractable Al and Fe concentrations, in both soil materials. Ash treatments increased seedling foliar K and Na concentrations in O horizon soils, but had little effect on growth. No significant effects on seedling properties from ash in B horizon soils were found. Fertilizer N treatments did not improve seedling growth in either soil material. Soil and seedling response to N were notably different for the different soils used. Based on this short-term study it appears that (a) land applications of wood-ash at the rates used may be a viable approach to recycling this solid waste, and (b) long-term studies are required to evaluate this practice under field conditions.     

Fine-Root Production and Aboveground Development for Loblolly Pine,Silver Maple,and Cottonwood

Fine-root production was studied in recently established loblolly pine (Pinus taeda), silver maple (Acer saccharinum), and cottonwood (Populus deltoides) biomass plantations. Dry weights of fine roots produced in ingrowth cores were recorded from April 2008 to March 2009 to quantify the temporal variation of fine-root production among the species. Similarly, fine-root production was compared to the monthly height and diameter increments, soil temperature, and moisture content. Species showed no significant difference in fine-root production; however, fine-root production varied by month. Fine-root production in September was significantly different from that of December and January combined, February, and May. Loblolly pine produced 49 g m^?2, whereas silver maple and cottonwood produced 37 g m^?2 and 35 g m^?2 of fine roots, respectively, during the study period. Fine-root production was not correlated with height increment, diameter increment, soil temperature, and soil moisture.     

Behavior of heavy metals in forest microcosms

Transport and distribution of heavy metals were determined in soil and vegetation (Acer Rubrum) of intact forest microcosms. Litter from a contaminated forest and baghouse dust from a primary Pb smelter were applied to three of the microcosms, while three uncontaminated microcosms served as controls. Total dosages for Ph, Cd, Zn, and Cu on the treated microcosms were 11.0, 0.128, 0,748, and 0.161 mg cm^?2, respectively. All metals were mobilized in soil and were enriched in at least one tissue component of Acer rubrum. Enrichment of Pb, Cd, and Zn occurred in all Acer tissues; Cu enrichment was found only in leaves. Uptake of metals by Acer rubrum was similar to a contaminated forest in southeastern Missouri and decreased in order: Zn, Cu, Cd, and Pb. Results of this experiment indicate that intact microcosms may be useful in assessing uptake and mobility of toxic chemicals which may be applied to forest ecosystems.     

Effects of simulated acid rain on the growth,nutrition, foliar pigments and photosynthetic rates of sugar maple and white spruce seedlings

Sugar maple (Acer saccharum Marsh.) and white spruce (Picea glauca (Moench) Voss) seedlings were exposed to simulated acid rain (SAR) of pH 3.2, 4.3 and 5.6 for two and one-half growing seasons. Ambient rain was excluded from the treatment plots by mobile rain exclusion canopies. Sugar maple seedlings treated with pH 3.2 SAR had significantly higher foliar concentrations of nitrogen, sulphur and manganese, compared to either the pH 4.3 or 5.6 treated seedlings. The pH 3.2 treated seedlings also tended to have greater growth and photosynthetic rates compared to the pH 4.3 and 5.6 treated seedlings. In contrast, the pH 3.2 treated white spruce seedlings tended to have decreased growth and lower foliar potassium concentrations relative to the pH 4.3 and 5.6 treated seedlings. Statistically there were no significant treatment differences in seedling height, seedling diameter, foliar pigments, or photosynthetic rates in either the sugar maple or white spruce seedlings.     

Temporal variation of mercury in vegetation

Temporal changes in the Hg content of balsam fir needles (Abies balsamea) and white spruce needles (Picea glauca) were monitored at a control site over two growing seasons. Results indicated a significant increase in the Hg content of needles of both species over the course of a growing season and from one year to the next. The Hg content of new foliage more than doubled within each growing season, and was 5–10 ng g^?1 higher in the 1990 growing season than in the previous year. These results indicate that temporal variation is a potential source of error when mapping the spatial variation of Hg concentrations in vegetation. To minimize this source of error, field surveys should be completed as quickly as possible (i.e., within two or three weeks).     

Mercury speciation in the Scheldt Estuary

Surface waters of the Scheldt Estuary were sampled on various occasions between 1991 and 1994. Longitudinal particulate Hg (PM) concentrations ranged from 0.4 – 1.7 μgHg/g and are essentially controlled by physical mixing of polluted fluvial particulates with relatively unpolluted marine particulates. Total dissolved mercury (TDM)concentrations ranged from 0.5 to 5.2 ng/L and are strongly influenced by removal and mobilization processes in the upper estuary, while in the lower estuary mixing processes cause a progressive decrease in TDM towards the mouth. Speciation studies showed that dissolved Hg is predominantly bound to strong complexing ligands (organic substances) in the upper estuary, but this fraction decreases with increasing salinity. In June 1993, however, the reactive mercury fraction was also high in the upper estuary. Model calculations showed that a conditional stability constant for Hg- humic acid interactions of 10¹⁹ was a good estimate for the Scheldt estuary. Dissolved methylmercury was analyzed on three occasions. Significant seasonal variations were observed with concentrations ranging from 11 to 120 pg/L in the winter and 80 to 400 pg/L in summer. Supersaturation of Hg° is observed throughout the whole estuary resulting in an estimated evasion flux of 140–1400 ng/m² day.     

Bryophyte species richness on boulders: relationship to area, habitat diversity and canopy tree species

Bryophytes growing on siliceous boulders (diameter 50-200 cm) were studied in two forests in east-central Sweden to investigate the influence of different canopy tree species on the bryophyte species richness. Granite boulders lying below crowns of Ulmus glabra (elm), Fraxinus excelsior (ash), Acer platanoides (maple), Quercus robur (oak), Betula pendula (birch), and Picea abies (Norway spruce) were studied in two mixed stands. Both boulder area and within-boulder habitat diversity were positively related to species richness. Boulders below the base-rich deciduous trees F. excelsior, U. glabra and A. platanoides held roughly twice as many species as those below P. abies, with Q. robur and B. pendula as intermediates. The rank order among trees was as expected from bark pH and litter decomposability in the literature. We also used sample plots to investigate species richness at a smaller scale. Within plots, intermediate levels of litter, inclination and exposed rock promoted species richness, and also the covering tree species had an effect. Individual plots were on average not more species-rich on large boulders than on small ones. This leads us to conclude that population extinctions on the plot-level, and re-colonisations from other parts of the boulder, are less important for species richness than within-boulder habitat diversity. Since species richness was lower under P. abies it is important to favour a diversity of tree species and to include base-rich deciduous trees in otherwise homogeneous Picea forests.     

Remnant sugar maple (Acer saccharum subsp. skutchii) populations at their range edge: Characteristics,environmental constraints and conservation implications in tropical America

Relationships between environmental conditions and persistence of populations at edges of ranges should be useful for predicting consequences of climate change. We characterized environmental conditions of six disjunct sites in Mexico and Guatemala that contain all known relict populations of the most southern subspecies of sugar maple, cloud forest sugar maple (Acer saccharum subsp. skutchii). We also sampled abundance and basal area of all tree species, recording 164 species, 92 genera (61% tropical), and 54 families at these sites. Temperate genera decreased in number from north to south, but mixtures of temperate and tropical species were co-dominant with cloud forest sugar maple at all sites. For all species, basal area was 24–52 m² ha^?1 and density was 990–2986 trees/ha at the six sites. Cloud forest sugar maple comprised 7–43% of total basal area and 1–16% of total densities at each site. Populations of cloud forest sugar maple currently are vulnerable to environmental change. Anthropogenic disturbance is negatively affecting four populations, and regeneration is successfully occurring in only two sites. As a result, densities and basal area are much reduced compared to more northern temperate populations. NMS-ordination indicated that elevation and hurricane frequency are major environmental constraints related to abundance. Maple recruitment is associated with short hurricane return intervals that maintain higher elevation cloud forests in states conducive for regeneration. We establish the conservation status of cloud forest sugar maple at the southern end of its range relative to expected climate change and propose this subspecies be included in the IUCN-Red List.     

Utilization of MSW Compost In Nursery Stock Production

This three year study was conducted to evaluate the suitability of municipal solid waste (MSW) compost as a soil amendment or a mulch to suppress weeds in the production of field grown nursery stock. In the soil amendment experiment, compost was applied at the rates of 0, 56, and 112 t/ha and incorporated into the soil prior to planting. In the mulch/weed control experiment, 224 t/ha of compost was applied to one set of plots as a mulch after planting and compared to plots treated with herbicide and untreated controls. Each plot in both experiments contained four rows with one each of red maple (Acer rubrum L.), sugar maple (Acer saccharum Marsh.), white pine (Pinus strobus L.), and pin oak (Quercus palustris Muenchh.). Mortality and weed counts were determined during the first growing season. Annual measurements of crown height, crown width, and caliper (at the 1 foot level) were made the following three winters. Two inches of compost mulch (224 t/ha) provided adequate weed control only in the first year. Mowing suppressed the weeds that invaded the plots beyond the first year. For maples, first year mortality in plots mulched with 224 t/ha compost or amended with 112 t/ha compost was significantly less than unamended controls. In subsequent years, the mulched maples grew more than trees in the unamended controls. In the plots amended with 56 or 112 t/ha compost, sugar maples had increased height, canopy, and caliper growth compared to the unamended controls. The hearty pin oak saplings survived transplanting and there was a significant increase in caliper growth in plots amended with 112 t/ha (1 inch) of compost. Mortality of white pine increased when mulched with 224 t/ha compost. Increased mortality was most likely due to high concentrations of ammonium and soluble salts in the immature compost. Beyond the first year, there were no negative impacts on the growth of white pine from any of the compost treatments.     

Input of Atmospheric Particles into Forest Stands by Dry Deposition

In this study the dry input of atmospheric particles into a forest stand is quantified. A wash-off-method using the natural leaf surfaces as collectors of the dry deposition was chosen. The direct on-site-measurement on living branches were achieved in a spruce stand (Picea abies (L.) Karst) at Solling, Germany. The ion exchange processes occurring on natural branches can reliably be quantified through immediate sequential washings. In order to calculate also the gas dry deposition of those trace elements which occur in both particle and gas phases, a resistance model was used. From these results the deposition velocity of particulate aerosol components into the forest stand was calculated. Dry particle deposition constitutes an important part of the total matter input into the forest ecosystem. Just the nitrogen input into Solling only by dry deposition (from particle-, mist-, and gas-deposition) with about 30 kg N ha^?1 a^?1 already exceeds the critical load of 20 kg N ha^?1 a^?1 by far, and this is without even considering the additional load by wet deposition which amounts to 15 kg ha^?1 a^?1. These findings are of greatest ecological importance, as the damage to the stability of the forest ecosystem caused by increased nitrogen input is considerable. Only a quick and drastic reduction of sulphur and nitrogen emissions could stop the further increase of the nutritient imbalance and the progressing acidification of this ecosystem.