Container-grown tree seedling responses to sodium chloride applications in different substrates

Seedlings of Norway maple (Acer platanoides), silver birch (Betula pendula), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were grown in selected sodium chloride (NaCl) concentrations, soil types and under different watering regimes. Plants were raised from seeds, except for Scots pine plants which were obtained from a commercial source. Among the plant species tested, Scots pine was the most tolerant to soil salinity, while Norway spruce was the most susceptible. For both Norway maple and Norway spruce some half-sib families were more tolerant than others. No significant correlation was found between the tolerance of different half-sib families and the tolerance of mother trees observed in the field. The extent of leaf necrosis correlated significantly with the leaf concentrations of sodium (Na) and chloride (Cl). Among half-sib families within the species no such correlation was found. On the other hand, the least injured progeny of Norway maples had the highest concentrations of NaCl. The extent of salt-induced leaf necrosis varied with soil type, and a significant interaction between species and soil type was observed. Seedlings of Norway spruce grown in sand showed more severe necrosis and significantly higher concentrations of Na and Cl than seedlings grown in loam, silt loam, and peat. The severity of salt-induced leaf injury varied with the watering regime. Silver birch was the most affected species by drought and autumn watering treatments. Plants of silver birch subjected to drought showed increased leaf necrosis compared to the non-treated plants, and autumn watering treatment reduced the severity of leaf necrosis.     

Prospects for cultivating white mulberry (Morus alba) in the drawdown zone of the Three Gorges Reservoir, China

Restoration of vegetation is the most viable management approach for restoring ecological functions in the drawdown zone (hydro-fluctuation belt) of the Three Gorges Reservoir. The selection of plants for this purpose is therefore critically important. Most indigenous plants are not adapted, however, to the counter-seasonal fluctuation of water levels and rapid changes of up to 30 m in water depth that characterize the management of the reservoir. As a result, the reservoir drawdown zone tends to be vegetation deficient. Mulberry (Morus alba L.) has attracted attention as a suitable woody plant for restoring woody vegetation because of its strong adaptation to environmental stresses and the finding that it survives up to 7 m of flooding in parts of the drawdown zone. Comprehensive evaluation of research is therefore required in order to provide guidance for the rational use of mulberry in vegetation restoration strategies for the drawdown zone. Knowledge of the physiology of mulberry adaptation to stress is reviewed here, along with a detailed review of the ecology and agricultural benefits and limitations of mulberry in the context of the Three Gorges Reservoir. It is proposed that a cultivation model for mulberry plants based on ecological principles should be adopted for use within the drawdown zone and that a wider range of biophysical and socio-economic research to develop this model further should be conducted in the future.     

Growth and physiology of Northern Red Oak: preliminary comparisons of mature tree and seedling responses to ozone

Considerable progress has been made during the past decade in the development of mechanistic models that allow complex chemical, physical, and biological processes to be evaluated in the global change context. However, quantitative predictions of the response of individual trees, stands, and forest ecosystems to pollutants and climatic variables require extrapolation of existing data sets, derived largely from seedling studies, to increasing levels of complexity with little or no understanding of the uncertainties associated with these extrapolations. Consequently, a project designed to address concerns associated with scaling from seedling to mature tree responses was initiated. During the 1990 and 1991 growing seasons, mature northern red oak (Quercus rubra L.) trees and seedlings were exposed to subambient, ambient, and twice ambient ozone (O(3)) concentrations. The initial focus of the study was to identify possible trends and obvious differences between mature trees and seedlings, both in terms of growth and physiology and in response to O(3). Generally, mature trees exhibited a greater decrease in photosynthesis rates over the growing season than did the seedlings. Ozone treatments had no consistent effect on gas exchange rates of seedlings, but the twice ambient O(3) treatment resulted in reduced photosynthesis rates in the mature tree. Despite no effect of O(3) on seedling gas exchange rates, total seedling biomass was significantly less at the end of the 1991 growing season for those seedlings exposed to twice ambient O(3) levels. Disproportionate reductions in root biomass also resulted in reduced root to shoot ratios at elevated O(3) concentrations.     

Interactions between Sitka spruce, the green spruce aphid, sulphur dioxide pollution and drought

Sitka spruce trees, with and without the aphid Elatobium abietinum and/or drought treatment, were subjected to 25 nl litre(-1) of sulphur dioxide over a 2-month period. Aphids became three times as abundant on the fumigated trees if they were well watered and twice as abundant on trees from which water was withheld, compared with unfumigated controls. Growth parameters of the trees were little affected by pollution alone, but were substantially reduced by either aphids or drought. There was a significant interaction between SO(2) and aphids in a further reduction of both leader extension and root weight. Root weight was also reduced by 24% more than expected from the additive effects of the combined SO(2) and drought treatment.     

A conceptual framework: Redefining forest soil's critical acid loads under a changing climate

Federal agencies of several nations have or are currently developing guidelines for critical forest soil acid loads. These guidelines are used to establish regulations designed to maintain atmospheric acid inputs below levels shown to damage forests and streams. Traditionally, when the critical soil acid load exceeds the amount of acid that the ecosystem can absorb, it is believed to potentially impair forest health. The excess over the critical soil acid load is termed the exceedance, and the larger the exceedance, the greater the risk of ecosystem damage. This definition of critical soil acid load applies to exposure of the soil to a single, long-term pollutant (i.e., acidic deposition). However, ecosystems can be simultaneously under multiple ecosystem stresses and a single critical soil acid load level may not accurately reflect ecosystem health risk when subjected to multiple, episodic environmental stress. For example, the Appalachian Mountains of western North Carolina receive some of the highest rates of acidic deposition in the eastern United States, but these levels are considered to be below the critical acid load (CAL) that would cause forest damage. However, the area experienced a moderate three-year drought from 1999 to 2002, and in 2001 red spruce (Picea rubens Sarg.) trees in the area began to die in large numbers. The initial survey indicated that the affected trees were killed by the southern pine beetle (Dendroctonus frontalis Zimm.). This insect is not normally successful at colonizing these tree species because the trees produce large amounts of oleoresin that exclude the boring beetles. Subsequent investigations revealed that long-term acid deposition may have altered red spruce forest structure and function. There is some evidence that elevated acid deposition (particularly nitrogen) reduced tree water uptake potential, oleoresin production, and caused the trees to become more susceptible to insect colonization during the drought period. While the ecosystem was not in exceedance of the CAL, long-term nitrogen deposition pre-disposed the forest to other ecological stress. In combination, insects, drought, and nitrogen ultimately combined to cause the observed forest mortality. If any one of these factors were not present, the trees would likely not have died. This paper presents a conceptual framework of the ecosystem consequences of these interactions as well as limited plot level data to support this concept. Future assessments of the use of CAL studies need to account for multiple stress impacts to better understand ecosystem response.     

New approaches to study the relationship between stomatal conductance and environmental factors under Mediterranean climatic conditions

The most frequently models used (Ball–Berry and Jarvis-type models) to estimate stomatal conductance (Gs) values have limitations when applied to plants growing in Mediterranean climate. To overcome these limitations, several statistical methodologies (Multiple Linear Regression, Neural Net Analysis (NNA)) were used to build models to predict Gs. However, all these models were unable to integrate the physiological response of plants to the overall limiting environmental parameters in our Mediterranean site especially during the summer drought. With this in mind, it is relevant to find alternative approaches which link Gs response to environmental limitations of plants. In this paper, we demonstrate that: (1) the different linear and nonlinear statistical approaches used significantly affect the weights of the environmental variables which are utilized in semi-empirical Gs models; (2) a tight relationship exists between summer values of Gs and the rate of accumulated precipitations (α) in the first 5 months of the year, thus allowing to predict Gs in a quantitative way; and (3) the latter is also related to different water-use strategies adopted by plants in response to drought stress in the summer period. Because α is easily calculated, it is an interesting parameter for the Gs modelling addressed to understand many important aspects of the plant–environment interactions, such as water relations and pollutant uptake.     

Shoot growth of mature Fagus sylvatica and Picea abies in relation to ozone

Epidemiological analysis of sequential growth data may be a tool in assessing ozone sensitivity of mature trees. Annual shoot growth of mature Fagus sylvatica in 83 Swiss permanent forest observation plots and of Picea abies in 61 plots was evaluated for 11 and 8 consecutive years, respectively, using branches harvested every 4 years. The data were assessed as annual deviation from average growth and related to fructification, ozone, meteorological parameters, and modelled soil water content using a mixed linear model. In beech, a significant association between ozone and shoot growth was observed which corresponded to a 7.4% growth reduction between 0 and 10 ppm h AOT40 (accumulated ozone over threshold 40). This is in the same order of magnitude as the response observed in experiments with seedlings. No interaction was found between ozone and drought parameters. In Norway spruce, shoot growth was neither associated with ozone nor with drought.     

Changes in susceptibility of beech (Fagus sylvatica) seedlings towards Phytophthora citricola under the influence of elevated atmospheric CO2 and nitrogen fertilization

The growth-differentiation balance hypothesis (GDBH) predicts changes in susceptibility of plants against herbivores with changing resource availability. In the presented study we tested the validity of the GDBH for trees infected with a root pathogen. For this purpose Fagus sylvatica seedlings grown under different atmospheric CO₂- and soil nitrogen regimes were infected with the root pathogen Phytophthora citricola. High nitrogen supply increased total biomass of beech regardless of the CO₂-treatment, whereas elevated CO₂ enhanced biomass only in the high nitrogen treatment. The responses of beech under the different growing regimes to the Phytophthora root infection were not in line with the predictions of the GDBH. Enhanced susceptibility of beech against P. citricola was found in seedlings grown under elevated CO₂ and low nitrogen supply. Fifteen months after inoculation these plants were characterized by enhanced water use efficiency, by altered root-shoot ratios, and by enhanced specific root tip densities.     

Growth, ectomycorrhizae and nonstructural carbohydrates of loblolly pine seedlings exposed to ozone and soil water deficit

Loblolly pine (Pinus taeda) seedlings from three full-sib families were exposed to 0, 50, 100 or 150 ppb ozone (O(3)) (5 h/d, 5 d/week for 6 or 12 weeks). Soil water potential was maintained near pot capacity (-0.03 MPa) or soil was allowed to dry to approximately -1.0 MPa and resaturated. Chlorotic mottling and flecking of needles due to O(3) injury were observed for seedlings from all pine families. Soil water deficit lessened the intensity of O(3) symptoms, possibly due to stomatal closure. Exposure to O(3) and soil water deficit each resulted in less seedling volume growth and dry weight, and changed the nonstructural carbohydrate content of seedlings compared with controls. Increasing O(3) concentrations resulted in a linear reduction in foliar starch content but did and affect hexose or sucrose content. Soil water deficit resulted in less starch and soluble sugar contents in above- and below-ground plant parts compared with controls. Soil water deficit did not affect numbers or percentages of roots that formed ectomycorrhizal tips. A linear dose-response relationship between O(3) and ectomycorrhizae was observed. The number of ectomycorrhizal tips/cm long root and the percentage of feeder roots that formed ectomycorrhizae were lower as O(3) concentration increased. Overall, each stress alone caused less seedling growth and carbohydrate content compared with controls, but only O(3) was responsible for suppression of ectomycorrhizae.     

Competition and facilitation in industrial barrens: variation in performance of mountain birch seedlings with distance from nurse plants

In stressful environments inter-plant facilitation is an important phenomenon co-occurring with competition. However, most experiments in natural ecosystems have only contrasted "sheltered" and "exposed" microsites, thus missing possible non-linearity of effects and not giving any information about the scale at which these interactions operate. In the current experiment we studied the net effect of nurse trees on mountain birch seedlings at various planting distances. Seedlings were planted in two highly stressful subarctic industrial barren sites around the nickel-copper smelter in Monchegorsk, NW Russia, at five distances (from 10 to 100 cm) from mature birch trees that were circa 100 cm in height. The survival and growth of seedlings were monitored for six years and the results were analyzed in respect to several environmental characteristics. Despite the fact that interaction strengths varied between years and between two study sites, both survival and growth of seedlings indicated optimum performance at middle distances and decreasing performance closer to and further from the nurse tree. We suggest that adverse effects on seedling performance at short distances are explained by competition and/or accumulation of pollutants under nurse plants, whereas at long distances these adverse effects appear due to lack of shelter, as shown by higher wind stress and lower soil water content.     

Biological activity of soil organic matter mobilized by root exudates

In order to study the biological activity of soil organic matter mobilized by agrarian (Zea mays: cultivars Mytos and Samantha) and forest (Picea abies Karst. and Pinus sylvestris L.) root exudates, two different soils, an Eutric Cambisol (EC) and a Rendzic Leptosol (RL), were considered. Soil organic matter extracts were obtained by treating the soils with water (control) or plant root exudates. The extracts were characterized by hormone-like activities and gas chromatographic/mass spectrometric (GC/MS) measurements. Their effects on the nitrogen metabolism in maize seedlings were evaluated. The nitrogen organification in the maize seedlings has been greatly stimulated by all the organic acid extracts from the agrarian soil, while the extracts from the forest soil had no influence upon the metabolism; this indicated a probable link between the plant and the environment. The different biological activities of the extracts are discussed.     

Dispersal and mobility of heavy metals in relation to tree survival in an aerially contaminated woodland soil

Nearly a century of metal deposition adjacent to a metal refinery in Prescot, north-west England has led to highly elevated metal levels in soils at a dominantly Acer pseudoplatanus woodland, but with incongruously and perplexingly few detrimental effects on trees. Dispersal and speciation of Cu, Cd, Zn, Pb and Ni in soil was found to be extremely variable, but spatial patterns of metals were inter-related and also related to soil pH and soil organic matter. These soil variables were all generally higher in soil directly beneath trees than in soil between trees, and were particularly high beneath the spreading canopy of Aesculus hippocastanum. It is argued that this heterogeneous dispersal and availability of metals in soils may explain the survival of mature trees and the successful establishment of seedlings within the woodland. Differing speciation and mobility has allowed high disappearance rates of metals since recent closure of the refinery, which may result in soil recovery at a faster rate than previously thought.     

Effect of La3+ on the activities of antioxidant enzymes in wheat seedlings under lead stress in solution culture

In order to improve the plant ability to resist lead stress, effect of 0.05 mg/l La(NO₃)₃ on the activities of catalase (CAT), superoxide dismutase (SOD), the level of malondialdehyde (MDA) in wheat seedlings under lead stress was studied. The effect of La³⁺ on plant growth, chlorophyll content in wheat seedlings after adding 0, 50, 100 mg/l Pb(NO₃)₃ to the nutrient solution for 12 days was observed. The plants were grown in nutrient solution in a strictly controlled climate growth room. Effects of La³⁺ (with La treatment) compared with check groups was evidently observed. The activities of SOD and CAT in root were enhanced 0.45–1.69 times and 33.20–77.77% respectively and MDA content was reduced 11.05–27.49% in root after treatments from the second day till the end of the experiment. The activities of SOD and CAT was found to be increased slightly (P<0.05) and MDA content decreased in shoot and root of wheat seedlings by La³⁺ under lead stress within five days after treatments compared with Pb1 and Pb2 groups. It was assumed that antioxidant enzymes was found to be increased by La(NO₃)₃, the antioxidant potential of the wheat seedlings to resist lead stress enhanced. It is suggested that La³⁺ could be used to resist lead stress at the beginning under stress while the stress was not so serious.     

Accumulation and spatial distribution of Cd, Cr, and Pb in mulberry from municipal solid waste compost following application of EDTA and (NH4)2SO4

Municipal solid waste compost can be used to cropland as soil amendment to supply nutrients and improve soil physical properties. But long-term application of municipal solid waste (MSW) compost may result in accumulation of toxic metals in amended soil. Phytoremediation, especially phytoextraction, is a novel, cost-effective, and environmentally friendly approach that uses metal-accumulating plants to concentrate and remove metals from contaminated soils. Ethylenediaminetetraacetate (EDTA) was applied to metal-contaminated soil to increase the mobility and phytoavailability of metals in soil, thereby increasing the amount of toxic metals accumulated in the upper parts of phytoextracting plants. The objectives of this study were (1) to investigate the accumulation and spatial distribution of toxic metals (Cd, Cr, and Pb) in mulberry from MSW compost with the application of EDTA and (NH₄)₂SO₄, (2) to examine the effectiveness of EDTA and (NH₄)₂SO₄ applied together on toxic metals (Cd, Cr, and Pb) removal by mulberry under field conditions, and (3) to evaluate the potential of mulberry for phytoextraction of toxic metals from MSW compost. The tested plant—mulberry had been grown in MSW compost field for 4 years. EDTA solution at five rates (0, 50, 100, 50 mmol L^?1?+?1 g?L^?1 (NH₄)₂SO₄, and 100 mmol L^?1?+?1 g?L^?1 (NH₄)₂SO₄) was added into mulberry root medium in September 2009. Twenty days later, the plants were harvested and separated into six parts according to plant height. Cd, Cr, and Pb contents in plant samples and MSW compost were analyzed using an atomic absorption spectrophotometer. In the same treatment, Cd, Cr, and Pb concentrations in mulberry shoot were all higher than those in root, and Cd and Pb concentrations in shoot increased from lower to upper parts, reaching the highest in leaves. Significant increases were found in toxic metal concentration in different parts of mulberry with increasing EDTA concentration, especially when combined with (NH₄)₂SO₄. Mulberry exhibited high ability to accumulate Cd with bioconcentration factors (BCFs) higher than 1. EDTA application also significantly increased Cd BCFs. More than 30 % of metal uptake was concentrated in mulberry branches (stem of above 100 cm height) and leaves. Results presented here show that mulberry is a woody plant that has the potential of Cd phytoextraction from MSW compost by removing leaves and cutting branches. The application of EDTA combined with (NH₄)₂SO₄ significantly enhanced the efficiency of mulberry in removing Cd from the compost medium. Adding (NH₄)₂SO₄ into the compost will lower the risk of the exposure of environment to excessive non-biodegradable EDTA in a large-scale EDTA-assisted phytoextraction by reducing the dosage of EDTA. In China, the need for sod is increasing day by day. Sod is often produced on arable soil and sold together with soils. This would lead to the soil being infertile and the soil layer thin. After several times’ production, the soil can no longer be used for cultivating crops and be destroyed. In order to fully utilize MSW compost resources and save valuable soil resources, MSW compost can be used to replace arable soil to produce sod after extraction of toxic metals in it.     

Physiology, morphology, and ozone uptake of leaves of black cherry seedlings, saplings, and canopy trees

Patterns of ozone uptake were related to physiological, morphological, and phenological characteristics of different-sized black cherry trees (Prunus serotina Ehrh.) at a site in central Pennsylvania. Calculated ozone uptake differed among open-grown seedlings, forest gap saplings, and canopy trees and between leaves in the upper and lower crown of saplings and canopy trees. On an instantaneous basis, seedling leaves had the greatest ozone uptake rates of all tree size classes due to greater stomatal conductance and higher concentrations of ozone in their local environment. A pattern of higher stomatal conductance of seedlings was consistent with higher incident photosynthetically-active radiation, stomatal density, and predawn xylem water potentials for seedlings relative to larger trees. However, seedlings displayed an indeterminate pattern of shoot growth, with the majority of their leaves produced after shoot growth had ceased for canopy and sapling trees. Full leaf expansion occurred by mid-June for sapling and canopy trees. Because many of their leaves were exposed to ozone for only part of the growing season, seedlings had a lower relative exposure over the course of the growing season, and subsequently lower cumulative uptake, of ozone than canopy trees and a level of uptake similar to upper canopy leaves of saplings. Visible injury symptoms were not always correlated with patterns in ozone uptake. Visible symptoms were more apparent on seedling leaves in concurrence with their high instantaneous uptake rates. However, visible injury was more prevalent on leaves in the lower versus upper crown of canopy trees and saplings, even though lower crown leaves had less ozone uptake. Lower crown leaves may be more sensitive to ozone per unit uptake than upper crown leaves because of their morphology. In addition, the lower net carbon uptake of lower crown leaves may limit repair and anti-oxidant defense processes.     

Combined effect of copper and prolonged summer drought on soil microarthropods in the field

Soil microarthropods experience a large range of natural stressors in their natural environment, e.g. variations in temperature and soil moisture, but also anthropogenic stressors such as soil pollutants. In the present study the combined effect of drought stress and copper pollution on microarthropods was investigated in a field study. We hypothesised that microarthropods in copper polluted soil would be more susceptible to drought than animals in control soil. Surprisingly, the abundance of microarthropods in autumn was positively affected by summer drought and copper pollution did not influence the effect of drought in a negative way. The stimulation was mainly seen as an increase of Acari, but also groups of Collembola were positively affected. We suggest that the positive effect of the enforced summer drought could be due to a rapid recovery, which further is accelerated by an increase of food resources (microbes) which have not been utilized during the drought.     

Growth dynamics of Chinese wingnut (Pterocarya stenoptera) seedlings and its effects on soil chemical properties under simulated water change in the Three Gorges Reservoir Region of Yangtze River

Pterocarya stenoptera is a native deciduous tree species and a candidate for reforestation in the riparian zones of the Three Gorges Reservoir Region of Yangtze River in China. Water treatments of continuous flooding (CF) and periodic flooding–drought (PF) were applied to examine the growth dynamics of 4-month-old P. stenoptera seedlings and its effects on soil chemical properties. Results showed that P. stenoptera seedlings in both CF and PF significantly decreased leaf biomass accumulation and the height and diameter growth as compared to that in control (CK; treatment with well-watered, well-drained soil), respectively. There was no significant difference in stem biomass among the three groups, but root biomass in PF showed severe reduction compared to that in both CK and CF. Total biomass in PF was significantly decreased compared to that in CK, but comparable to that in CF. Furthermore, no significant difference was found between CF and CK in total biomass. Water treatments in the unplanted soil pots significantly influenced soil pH, soil organic matter (OM), total nitrogen (TN), and alkali hydrolysable nitrogen (AN) contents, in contrast to no significant effects in total phosphorus (TP), total potassium (TK), available phosphorus (AP), and available potassium (AK) contents. In P. stenoptera soils, there were significant effects by water treatment, time, and treatment × time in the eight tested soil chemical properties, except treatment in TK and time effect in OM content. Compared to unplanted soils, the growth of P. stenoptera seedlings significantly increased soil pH value and OM, TN, TP, and TK contents, while decreasing AN, AP, and AK contents in CK group, augmented the mean value of each of the tested soil chemical properties with an exception of AK content in CF group, and increased soil pH value and TN, AN, TP, and AP contents with no significant differences in OM, TK, and AK contents in PF group. Given the fact that TN and TP contents significantly increased in P. stenoptera soils as compared to those in unplanted soils, growth of P. stenoptera seedlings should be a successful candidate for restoration within the highly dynamic hydrologic zone of the riparian zones of the Three Gorges Reservoir Region.     

Effect of landfill leachate irrigation on red maple (Acer rubrum L.) and sugar maple (Acer saccharum Marsh.) seedling growth and on foliar nutrient concentrations

Greenhouse experiments were conducted to investigate the nature and severity of stresses imposed on northern hardwood tree species (red maple (Acer rubrum L.) and sugar maple (Acer saccharum Marsh.)) by the application of municipal landfill leachate. Red maple seedlings received applications of untreated and pretreated (lime, activated carbon) leachate, to both leaves and soil, at irrigation rates consistent with evapotranspirational demands. Plant height measurements indicated no significant growth effects arising from leachate application over a 7-week period. Stem diameter, however, was positively affected by applications of both untreated and lime-treated leachate diluted to 75% with deionized water. Iron foliar concentrations were significantly higher in seedlings irrigated with untreated leachate applied to leaves and soil, but not in seedlings where leachate was applied to soil only. Nitrogen foliar concentrations were substantially higher in seedlings receiving undiluted and untreated leachate applied to the soil only. The Cu concentration of the red maple foliage decreased appreciably in plants receiving moderate applications of leachate. Foliar Ca concentrations decreased notably in seedlings irrigated with untreated leachate applied to the soil and with diluted, carbon-treated leachate. The Cu concentration of the red maple foliage decreased appreciably in plants receiving applications of undiluted and 50% water-diluted lime-treated leachate while Mn levels were consistently high across all treatments. Leachate application did not cause any discernable changes in foliar concentrations of P, K, Mg, B or Zn. In an ancillary experiment, sugar maple seedlings were subjected to saturation/ drainage treatment cycles with undiluted and untreated leachate. Severe visible symptoms of vegetative stress were apparent within 24 h and 100% seedling mortality occurred after five such waterlogging cycles. Fe assimilation was apparent in both leachate treatments relative to the 24 h water treatment. Despite the short-term nature of the experiments, the results indicate how quickly forest vegetation may respond to altered chemical environments. This underscores the need for correct installation and control of leachate irrigation systems.     

Germination, growth and gas exchange of selected boreal forest seedlings in soil containing oil sands tailings

Greenhouse experiments were conducted to determine the effects of soil enriched in fine tailings (FT), produced by the oil sands extraction, on germination, seedling growth and physiology of several plant species of the boreal forest. The germination of seeds was initially delayed by 15% FT in dogwood (Cornus stolonifera Michx) and jack pine (Pinus banksiana Lamb) but not in white spruce [Picea glauca (Moench) Voss]. In the second set of experiments we showed that all dogwood seedlings survived 6 months of treatment with 15% FT while the survival rates of raspberry, jack pine and white spruce seedlings were reduced to 44, 55 and 94%, respectively. FT reduced root and shoot dry weights in raspberry seedlings and the number of lateral shoots in jack pine and white spruce seedlings. In raspberry and jack pine seedlings, reductions of gas exchange were recorded. The results of our study suggest that the modifications of soil chemistry, texture and structure by FT may all contribute to the observed phytotoxic effects.     

Behavior and fate of chlorpyrifos introduced into soil-crop systems by irrigation

The effect of chlorpyrifos added in irrigation water to a red soil from Central South China on the growth of wheat and oilseed rape seedlings, together with its uptake, was studied in a pot experiment. Addition of chlorpyrifos (1-10 microg g-1) in a single irrigation with distilled water resulted in absorption of chlorpyrifos by wheat (0.257-4.50 microg g-1) and also oilseed rape seedlings (0.249-2.02 microg g-1) during 20 d of plant growth. An initial concentration of chlorpyrifos in soil that is equivalent to or below 10 microg g-1 did not significantly influence the growth of wheat seedlings. Similarly, an initial concentration equivalent to or below 5 microg g-1 did not significantly influence the growth of oilseed rape seedlings. The degradation rate of chlorpyrifos was 1.4-4.2 times larger in oilseed rape rhizosphere soil than in unvegetated soil. The numbers of bacteria and fungi in oilseed rape rhizosphere soil were 3.18 times and 1.84 times larger, respectively, than those in unvegetated soil. This helps to explain the difference in degradation rates obtained.