Black Spruce Seedlings Research Articles

Using cover crops to establish white and black spruce on abandoned agricultural lands

Vegetation control is a critical factor in reforestation. On abandoned agricultural lands, an alternative to herbicide application is the use of cover crops to compete with the weeds and to improve survival and growth rates of transplanted species. A factorial experiment was carried out on four sites to test this hypothesis. The experiment included three factors. The first factor consisted of lime versus no lime application. The second factor included four cover crop combinations and a control. Cover crop combinations were winter barley (Hordeum vulgare) underseeded with either birdsfoot trefoil (Lotus corniculatus), Kentucky bluegrass (Poa pratensis), ladino clover (Trifolium repens), or a mixture of Kentucky bluegrass and ladino clover. The third factor consisted in planting either white (Piceaglauca) or black (Picea mariana) spruce seedlings. Winter barley did not establish as rapidly and vigorously as expected. Nevertheless, the cereal reduced weed populations in the establishment year. For broadleaf weeds, this reduction was not large enough to allow a carryover during subsequent years. In contrast, subsequent increase of the grassy weed populations was slowed down in the presence of cover crops. The establishment of the other cover crops was poor and highly variable from site to site. It is not clear whether this relative failure was due to growing conditions, poor establishment of the cereal cover crop, or to other factors. Liming and cover crops had little effect on spruce growth but black spruce seedlings grew taller than white spruce seedlings at two out of four sites, and basal diameter of white spruce reached larger values than did black spruce. For white spruce, this might constitute an advantage in old fields where seedlings are prone to lodging under weed pressure. Finally, it was noted that seedling survival was exceptionally high in all treatments.

Invertebrate predation of postdispersal seeds and juvenile seedlings of black spruce (Picea mariana) in the boreal forest of eastern Canada

We used an extensive vertebrate exclosure experiment to evaluate black spruce (Picea mariana (Mill.) B.S.P.) postdispersal seed and seedling predation by invertebrates in three boreal habitats of Eastern Canada: recent burn, spruce–moss, and lichen woodland. Between 9% and 19% of seeds were eaten by invertebrates. Seed predation was higher in recent burns than in spruce–moss and lichen woodlands. Abundance and diversity of potential invertebrate seed consumers sampled in pitfall traps also varied among habitat types. Among the invertebrate seed consumers sampled, Myrmica spp. (Hymenoptera: Formicidae) and Pterostichus adstrictus (Eschscholtz, 1823) (Coleoptera: Carabidae) were the most numerous; Formica spp. (Hymenoptera: Formicidae) and Pterostichus punctatissimus (Randall, 1838) (Coleoptera: Carabidae) were also present. Between 2% and 12% of juvenile black spruce seedlings were eaten by invertebrates. The most important seedling consumers were slugs (molluscs). Invertebrate predation of seeds and seedlings was highest (19% and 12%) in recent burns, indicating that invertebrate predation may significantly influence black spruce regeneration in these sites.

Root Rot of Black Spruce Caused by Cylindrocladium canadense in Eastern North America.

During October 2002, symptoms of root rot of black spruce, Picea mariana (Mill.) B.S.P., were observed in the St-Modeste (47°46'N, 69°36'W) conifer nursery (400 km northeast of Montreal, Quebec, Canada). Disease severity was low in the greenhouse-produced mother plants and 1-year-old seedlings and moderate in field-grown 2- and 3-year-old seedlings. A species of Cylindrocladium was isolated on potato dextrose agar from 12 symptomatic seedlings from the greenhouse and 12 from the field. The isolates produced chestnut-colored colonies and chlamydospores, both of which were typical of C. canadense Kang, Crous & Schoch (2). DNA was extracted from representative isolates (MTF 101, MTF 102), and the internal transcribed spacer (ITS) of the rDNA gene was amplified and sequenced (GenBank Accession Nos. AY705980 and AY705981). There was a 99% match with a sequence of C. canadense (GenBank Accession No. AF348256). However, there was approximately 10% divergence with the ITS sequence of C. floridanum (GenBank Accession No AF307343). MTF101 and MTF102 were pathogenic on black spruce seedlings when fungal suspension (106 CFU/ml) was added to germinating seeds in petri plates or infiltrated into roots of 2-week-old seedlings growing in sterilized, moist, sandy soil in the greenhouse. Within 3 weeks, inoculated seedlings exhibited typical root necrosis, while control seedlings were symptomless. C. canadense was reisolated only from symptomatic seedlings. The occurrence of C. canadense in eastern North America has significant implications for forestry regeneration. Previously, only C. floridanum had been reported as pathogenic in the St-Modeste nursery and in eastern North America(1).

Black spruce seedlings in a Kalmia–Vaccinium association: microsite manipulation to explore interactions in the field

We established a field trial on an ericaceous-dominated clearcut in Quebec to determine the effect of Kalmia angustifolia L., Vaccinium angustifolium (Ait.), and V. myrtilloides (Michx.) on the growth and physiology of black spruce (Picea mariana (Mill.) BSP) seedlings and on soil characteristics over the first two growing seasons. Plots undergoing one of three treatments (shrub removal, humus removal, or undisturbed control) were planted with black spruce seedlings that were either unfertilized or spot fertilized at time of planting. In some of the undisturbed control plots, we also used 15NH415NO3 to compare uptake of broadcast N fertilizer by vegetation. The ericaceous shrubs had a significant negative impact on seedling growth. Growth reductions were not related to water stress, soil temperature, or soil moisture. Extractable NH4-N and P concentrations in mineral soil tended to decrease in the presence of ericaceous shrubs, but effects were not significant. Seedling foliar N concentration was also reduced in the presence of ericaceous shrubs. Of the total amount of 15N fertilizer found in vegetation, 64% was immobilized in Vaccinium spp., 31% in Kalmia, and 5% in black spruce, but spruce took up more 15N per unit of root biomass than the ericaceous shrubs. Kalmia had consistently higher predawn xylem water potentials than black spruce.

Effects of soil temperature on ecophysiological traits in seedlings of four boreal tree species

One-year-old seedlings of black spruce (Picea Mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss.), jack pine (Pinus banksiana Lamb.) and aspen (Populus tremuloides Michx.) were exposed to 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures for 4 months. The rate of net photosynthesis (A), stomatal conductance, mid-day xylem water potential, the internal to ambient CO2 concentration ratio (Ci/Ca), and specific leaf area (SLA) were evaluated 3 months after the initiation of the treatments. The responses of the above variables generally showed a bell-shaped curve except the Ci/Ca ratio. The relationships between soil temperature and the ecophysiological variables (except Ci/Ca) were modeled using third-order polynomials. The models suggest that jack pine generally had the highest optimal soil temperature among the four species, followed sequentially by black spruce, trembling aspen and white spruce. Aspen was generally more sensitive to low soil temperatures than the conifers while black spruce was more sensitive to high soil temperatures than other species. Jack pine and trembling aspen generally showed different response patterns than black and white spruce. The photosynthesis in aspen and jack pine was progressively less limited by stomatal conductance (relative to mesophyll limitation) as soil temperature increased from 5 to 35 °C whereas in the spruces, stomatal conductance was the least limiting to photosynthesis at moderate soil temperatures (10–15 °C for white spruce, 15–20 °C for black spruce). The xylem water potential of jack pine and aspen was more sensitive to low soil temperatures while that of the spruces was more sensitive to high soil temperatures. The specific leaf area of jack pine and aspen showed large variations with changes in soil temperature while that of the spruces was relatively constant throughout the range of soil temperatures. Most of the conifer seedlings in the 35 °C soil temperature treatment died at the end of the experiment while all aspen seedlings survived.

Molecular profiling of rhizosphere microbial communities associated with healthy and diseased black spruce (Picea mariana) seedlings grown in a nursery.

Bacterial and fungal populations associated with the rhizosphere of healthy black spruce (Picea mariana) seedlings and seedlings with symptoms of root rot were characterized by cloned rRNA gene sequence analysis. Triplicate bacterial and fungal rRNA gene libraries were constructed, and 600 clones were analyzed by amplified ribosomal DNA restriction analysis and grouped into operational taxonomical units (OTUs). A total of 84 different bacterial and 31 different fungal OTUs were obtained and sequenced. Phylogenetic analyses indicated that the different OTUs belonged to a wide range of bacterial and fungal taxa. For both groups, pairwise comparisons revealed that there was greater similarity between replicate libraries from each treatment than between libraries from different treatments. Significant differences between pooled triplicate samples from libraries of genes from healthy seedlings and pooled triplicate samples from libraries of genes from diseased seedlings were also obtained for both bacteria and fungi, clearly indicating that the rhizosphere-associated bacterial and fungal communities of healthy and diseased P. mariana seedlings were different. The communities associated with healthy and diseased seedlings also showed distinct ecological parameters as indicated by the calculated diversity, dominance, and evenness indices. Among the main differences observed at the community level, there was a higher proportion of Acidobacteria, Gammaproteobacteria, and Homobasidiomycetes clones associated with healthy seedlings, while the diseased-seedling rhizosphere harbored a higher proportion of Actinobacteria, Sordariomycetes, and environmental clones. The methodological approach described in this study appears promising for targeting potential rhizosphere-competent biological control agents against root rot diseases occurring in conifer nurseries.

Irrigation Control and Physiological Responses of Nursery-grown Black Spruce Seedlings (1+0) Cultivated in Air-slit Containers

Air-slit containerized (IPL 25-350A) black spruce [Picea mariana (Mill) BSP; 1+0] seedlings, were subjected to four irrigation regimes (IR-15%, IR-30%, IR-45%, and IR-60%, by volume, cm3 water/cm3 substrate) under tunnel conditions in a forest nursery. Irrigation regimes were controlled by time-domain reflectometry during the first growing season. With exception of midday water potential, water relation and gas exchange variables were unaffected by substrate water content. There were no significant differences in height, diameter or number of needle primordia of the seedlings grown under IR-15%, IR-30%, and IR-45%. Seedlings grown in a substrate with a high water content (IR-60%) had lower oven-dry biomass and higher cuticular transpiration rates than seedlings grown under the three other irrigation regimes. Root hydraulic conductivity was not affected by irrigation regime, but showed a general decrease towards the end of the growing season. Variation in root hydraulic conductivity was most likely related to root growth and degree of lignification. Seedlings that had been exposed to IR-60% during the first growing season remained smaller than the other seedlings throughout the second growing season. Results of this study indicate that nursery managers can reduce the quantity of irrigation water used without significantly affecting the growth or physiology of air-slit containerized black spruce seedlings (1+0) grown under tunnel conditions.

Root plug effects on early growth and nutrition of container black spruce seedlings

The capacity of root plugs of containerized stock to serve as a ready nutrient source for growth and nutrition of newly planted seedlings is not well understood. Intact and barerooted container-reared seedlings were planted on soil bioassays of contrasting fertility to examine the contribution of the root plug to early field performance, and test if nutrient loading and (or) site enrichment may enhance this effect. The test species was black spruce ( Picea mariana (Mill.) BSP) fertilized conventionally or nutrient loaded (at 10 or 64 mg N per plant for the season) in the nursery. The bioassays, retrieved from a boreal forest in northern Ontario, were topdressed with 20–20–20 fertilizer at 0 and 200 kg N ha −1 at planting to simulate nutrient “poor” and “rich” sites. Without changing total biomass, nutrient loading raised root plug electrical conductivity by 67%, and built up plant N, P and K reserves by 152, 32 and 33%, respectively. One season after outplanting, nutrient loading increased biomass, N, P and K accumulation of seedlings as high as 35, 43, 27 and 41%, demonstrating the effectiveness of this practice in improving early growth and nutrition. Element content differences between barerooted and intact seedlings suggest that root plugs contributed as much as 22, 17 and 34% to respective plant N, P and K uptake, signifying that root plugs act as important reserves for meeting nutrient requirements of container stock. Barerooting reduced height growth, shoot:root ratio and nutrient uptake of seedlings, particularly on the fertile (rich) site, but nutrient loading countered this inhibition somewhat. Study results confirm the importance of root plugs as immediate nutrient sources for fast growing trees, and suggest that supplemental fertilization prior to outplanting may benefit initial plantation establishment.

Effects of soil temperature on ecophysiological traits in seedlings of four boreal tree species

One-year-old seedlings of black spruce ( Picea Mariana (Mill.) B.S.P.), white spruce ( Picea glauca (Moench) Voss.), jack pine ( Pinus banksiana Lamb.) and aspen ( Populus tremuloides Michx.) were exposed to 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures for 4 months. The rate of net photosynthesis ( A), stomatal conductance, mid-day xylem water potential, the internal to ambient CO 2 concentration ratio ( C i/ C a), and specific leaf area (SLA) were evaluated 3 months after the initiation of the treatments. The responses of the above variables generally showed a bell-shaped curve except the C i/ C a ratio. The relationships between soil temperature and the ecophysiological variables (except C i/ C a) were modeled using third-order polynomials. The models suggest that jack pine generally had the highest optimal soil temperature among the four species, followed sequentially by black spruce, trembling aspen and white spruce. Aspen was generally more sensitive to low soil temperatures than the conifers while black spruce was more sensitive to high soil temperatures than other species. Jack pine and trembling aspen generally showed different response patterns than black and white spruce. The photosynthesis in aspen and jack pine was progressively less limited by stomatal conductance (relative to mesophyll limitation) as soil temperature increased from 5 to 35 °C whereas in the spruces, stomatal conductance was the least limiting to photosynthesis at moderate soil temperatures (10–15 °C for white spruce, 15–20 °C for black spruce). The xylem water potential of jack pine and aspen was more sensitive to low soil temperatures while that of the spruces was more sensitive to high soil temperatures. The specific leaf area of jack pine and aspen showed large variations with changes in soil temperature while that of the spruces was relatively constant throughout the range of soil temperatures. Most of the conifer seedlings in the 35 °C soil temperature treatment died at the end of the experiment while all aspen seedlings survived.

Root plug effects on early growth and nutrition of container black spruce seedlings

Root plug effects on early growth and nutrition of container black spruce seedlings

Persistence of early growth of planted Picea mariana seedlings following clear-cutting and drainage in Quebec wetlands

A study was carried out to test the persistence of the early effects of forest drainage and planting position on the growth of black spruce (Picea mariana (Mill.) BSP) seedlings planted in eight drained forested wetland cutovers. Initial results, 2 years after planting, had shown that seedling response was most affected by planting position within the microtopography, and to a lesser extent, by distance to the drainage ditch. Persistence of these effects was tested by measuring the survival and growth rates of seedlings for an additional 4 years after planting. Increased growth owing to raised planting position was maintained over time. The small effect of distance to ditch on seedling growth observed after two growing seasons did not evolve into larger differences over time, and after 6 years there was no significant effect of distance to drainage ditch. Given the marginal growth improvements of black spruce seedlings planted closer to the ditch, drainage networks with narrow ditch spacing are not necessary on these site types after clear-cutting.

Régénération artificielle des pessières noires à éricacées : effets du scarifiage, de la fertilisation et du type de plants après 10 ans

Site invasion by ericaceous shrubs after perturbation, either natural or human, is a major concern on some sites of the boreal forest of Québec. A dense cover of ericaceous shrubs often induces a conifer "growth check," which can last several decades. An interaction study was initiated in 1991 with the general objective of developing silvicultural strategies to ensure plantation success on such sites. Black spruce, jack pine, and tamarack seedlings were planted. Stock type, scarification, and fertilization treatments were organised in a randomized block split plot design. We measured seedling total height periodically over a ten-year period and assessed basal area and survival ten years after plantation. Most responses to treatments were additive. Results indicated that mechanical soil scarification is of major importance to ensure seedling growth, both in height and basal area, on spruce-ericaceous shrub sites of northeastern Québec. Scarification allowed a better expression of the site index, implying a sustainable impact on microsite characteristics that is greater than short-term effects on mineralization and nutrient availability. Fertilization positively influenced seedling growth, but less than soil scarification. Species choice had a strong impact on site productivity. Over a ten-year period, stock types only had a minor influence on plantation success, when compared to scarification or fertilization effects. Key words: Kalmia angustifolia, ericaceous shrubs, survival, growth, regeneration, black spruce, jack pine, tamarack

Ecophysiological adaptations of black spruce ( Picea mariana ) and tamarack ( Larix laricina ) seedlings to flooding

Black spruce (Picea mariana (Mill.) B.S.P.) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in boreal peatlands. The effects of 34 days of flooding on morphological and physiolog- ical responses were investigated in the greenhouse for black spruce and tamarack seedlings in their second growing season (18 months old). Flooding resulted in reduced root hydraulic conductance, net assimilation rate and stomatal conductance and increased needle electro- lyte leakage in both species. Flooded tamarack seedlings maintained a higher net assimilation rate and stomatal conductance compared to flooded black spruce. Flooded tamarack seedlings were also able to maintain higher root hydraulic conductance compared to flooded black spruce seedlings at a comparable time period of flooding. Root respiration declined in both species under flooding. Sugar concentration increased in shoots while decreasing in roots in both species under flooding. Needles of flooded black spruce appeared necrotic and electrolyte leakage increased over time with flooding and remained signif- icantly higher than in flooded tamarack seedlings. No visible damage symptoms were observed in flooded tamarack seedlings. Flooded tamarack seedlings devel- oped adventitious roots beginning 16 days after the start of flooding treatment. Adventitious roots exhibited significantly higher root hydraulic conductivity than similarly sized flooded tamarack roots. Flooded black spruce lacked any such morphological adaptation. These results suggest that tamarack is better able to adjust both morphologically and physiologically to prolonged soil flooding than black spruce seedlings.

Responses of black spruce (Picea mariana) and tamarack (Larix laricina) to flooding and ethylene.

Black spruce (Picea mariana (Mill.) BSP) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in the boreal peatlands of Alberta, Canada, where low nutrient availability, low soil temperature and a high water table limit their growth. Effects of flooding for 28 days on morphological and physiological responses were investigated in greenhouse-grown black spruce and tamarack seedlings in a growth chamber. Flooding reduced root hydraulic conductance, net assimilation rate and stomatal conductance, and increased water-use efficiency (WUE) and needle electrolyte leakage in both species. Although flooded black spruce seedlings maintained higher net assimilation rates and stomatal conductance than flooded tamarack seedlings, flooded tamarack seedlings were able to maintain higher root hydraulic conductance than flooded black spruce seedlings. Needles of flooded black spruce developed tip necrosis and electrolyte leakage after 14 days of flooding, and these symptoms were subsequently more prominent than in needles of flooded tamarack seedlings. Flooded tamarack seedlings exhibited no visible injury symptoms and developed hypertrophied lenticels at their stem base. Application of exogenous ethylene resulted in a significant reduction in net assimilation, stomatal conductance and root respiration, whereas root hydraulic conductivity increased in both species. Thus, although flooded black spruce seedlings maintained a higher stomatal conductance and net assimilation rate than tamarack seedlings, black spruce did not cope with the deleterious effects of prolonged soil flooding and exogenous ethylene as well as tamarack.

Hydraulic adjustment in jack pine and black spruce seedlings under controlled cycles of dehydration and rehydration.

Drought adjustments were compared in black spruce (Picea mariana[Mill] B.S.P), and jack pine (Pinus banksiana[Lamb.]) by subjecting seedlings to five cycles of dehydration and rehydration. A computer-controlled root misting chamber system, supplied low (-1.5 MPa), moderate (-2.0 MPa), and severe (-2.5 MPa) dehydration, respectively, in cycles 1, 3 and 5. Although cell water relations failed to adjust to chronic dehydration, there was limited osmotic adjustment in black spruce (cycle 3), and water was re-allocated from the apoplast to the symplast in jack pine (cycles 1 and 3). Dehydration postponement was more important than dehydration tolerance. Jack pine was better able to postpone dehydration than black spruce. Specific conductivity, the hydraulic conductivity per unit stem cross-sectional area, was lower in jack pine and slower to decline during chronic dehydration. When specific conductivity was corrected for the greater leaf area in black spruce, the leaf-specific conductivity did not differ in the two species. There was no increase in needle leakage in jack pine and stomata in jack pine seedlings reopened fully after rehydration. Black spruce was more of a 'water spender', and less water stress (-2.0 MPa, cycle 3) was required to lower specific conductivity, compared to jack pine (-2.5 MPa, cycle 5). Leakage from needle membranes increased in black spruce, and stomata failed to reopen after rewatering (cycles 3 and 5). A greater needle area, smaller root system, and a higher specific conductivity lowered the water stress threshold for cavitation in black spruce, which is confined to moister sites in the boreal forest. Jack pine had a larger root system, smaller needle area and lower specific conductivity than black spruce. Because of these static features, jack pine is more drought tolerant and it is often found on sites that are too hot and dry for black spruce.

Characterizing the frost sensitivity of black spruce photosynthesis during cold acclimation.

We used photosynthetic light response curves to measure and model the responses of two provenances of 3-year-old black spruce (Picea mariana (Mill.) BSP) seedlings to severe artificial frost treatments applied at 2-week intervals during cold acclimation. Black spruce seedlings responded to cold acclimation with long-term suppression of photosynthetic capacity (Amax) and apparent quantum-use efficiency (alpha'). Short-term reductions in both photosynthetic parameters following frost treatments were dependent on the extent of cold acclimation of the seedlings and the severity of the frost treatments. Large reductions in Amax in response to the frost treatments were observed in seedlings that had undergone little cold acclimation and these reductions were associated with an irreversible reduction in alpha'. Such seedlings recovered only partially during the subsequent 23 days, whereas seedlings in most other treatments showed complete recovery of Amax after 13 days. The impact of frost treatments on Amax and alpha' did not vary with seedling provenance. We propose an algorithm that predicts the combined effects of cold acclimation and severe freezing temperatures on the extent of the suppression of A(max) during autumn. The algorithm is based on (1) the maximum Amax observed during the growing season, (2) the accumulation of cold degree-days, based on a minimum nocturnal temperature < 5 degrees C, and (3) the severity of freezing temperatures during autumn. The parameters developed in the algorithm showed that cold acclimation of black spruce seedlings had a greater impact on the reduction of Amax in autumn than did the severe frost treatments. Mean Amax of seedlings subjected to artificial frosts showed a strong correlation with values predicted by the algorithm (r2 = 0.91).

Effets de différentes régies d'irrigation sur la croissance, la nutrition minérale et le lessivage des éléments nutritifs des semis d'épinette noire (1+0) produits en récipients à parois ajourées en pépinière forestière

To reduce the quantity of irrigation water used and the amount of mineral nutrients lost because of leaching, we used time domain reflectometry to monitor and maintain four irrigation regimes (15, 30, 45 and 60%, v/v) during the first growing season for 1+0 black spruce (Picea mariana (Mill.) BSP) seedlings. The seedlings were produced in air-slit containers (IPL 25–350A), filled with a peat substrate and were grown under a polyethylene tunnel at a forest nursery. Similar fertility levels were maintained in all four irrigation regimes even though the water content of the substrate could be very low (15 and 30%). Irrigation regime did not affect growth, root architecture or tissue nutrient contents at the end of the growing season. Monitoring water use over the course of the growing season clearly showed that the amount of irrigation water could be reduced by 62 to 76% without compromising seedling quality relative to the 60% irrigation regime. Leachate losses varied exponentially as a function of irrigation regime. The mean amount of water leached, relative to the quantity of water applied during the sampling period, was 10, 7.1, 28.4, and 62.2% for the 15, 30, 45, and 60% irrigation regimes, respectively. The losses of mineral nitrogen at the beginning of August were 49.7, 35.9, 55.2, and 88.2%, respectively, for the 15, 30, 45, and 60% irrigation regimes. To optimize irrigation and decrease leaching, a dynamic model for irrigation management is proposed that accounts for the phenological development of black spruce seedlings grown under tunnel conditions in forest nurseries.

ECOPHYSIOLOGICAL STUDY OF SUITABILITY OF PICEA MARIANA L. FOR AFFORESTATION IN ALKALIZED TERRITORIES IN NORTHEAST ESTONIA

The present paper is based on experiments carried out with black spruce (Picea mariana (Mill.) B.S.P.) in an industrial area in Northeast Estonia. Two-year-old seedlings of black spruce were planted in a sample plot affected by a cement plant and in an unpolluted control sample plot in 1990. At the end of the experiment in 1997 it was ascertained that the impact of industrial alkaline air pollution complexes resulting in the alkalization and chemical deviations of growth conditions decreases the content of carbohydrates and disbalances the mineral element composition in different organs of trees. Changes in the physiology of trees retard the growth and bring about a decrease in total biomass. The sturdiness quotient was higher and the Dickson quality index was lower than the control, indicating serious damages of trees in the polluted area. Increasing share of needles in the total biomass in polluted areas in comparison with control trees suggests that compensation mechanisms were started in trees to increase the assimilating mass in order to survive under stress.

Interactions among Kalmia angustifolia, soil characteristics, and the growth and nutrition of black spruce seedlings in two boreal Newfoundland plantations of contrasting fertility

To determine the nature of the negative influence of Kalmia angustifolia L. on black spruce (Picea mariana (Mill.) BSP) seedling growth and foliar nutrient concentrations, the effect of proximity to Kalmia on spruce seedlings was studied on two Kalmia-dominated sites of contrasting soil characteristics in central Newfoundland. Spruce seedlings and the soil at the base of their stems were sampled, and spruce leader length and foliar N and P concentration, as well as various physicochemical soil characteristics, were determined. Path analysis was used to determine the strength of direct and indirect relationships among variables hypothesized to be causally linked. Path diagrams were generated based on current knowledge of nutrient cycling in boreal ecosystems and mechanisms previously hypothesized to account for the influence of Kalmia on black spruce. On the wetter and richer site, proximity to Kalmia was associated with reduced spruce growth and humus extractable NH4-N, suggesting nutrient competition. On the drier and poorer site, results were consistent with a direct negative effect of Kalmia on the N nutrition of spruce. On both sites, we also found evidence for a direct effect of Kalmia on spruce growth that is consistent with allelopathic effects on spruce function.

Mechanisms of interaction between Kalmia angustifolia cover and Picea mariana seedlings

Sites dominated by Kalmia angustifolia L. are often associated with slow decomposition of organic matter, decreased nitrogen (N) mineralization rates, and low black spruce (Picea mariana (Mill.) BSP) productivity. The objective of this study was to separate the effects of belowground competition by Kalmia from the effects of water-soluble soil phenols on black spruce seedlings growing under different levels of Kalmia cover. A factorial greenhouse bioassay was established in which black spruce seedlings were grown for 6 months in intact blocks of soil with three different levels of Kalmia cover. The soil was treated with charcoal to reduce the amounts of water-soluble phenols, and (or) tubes were inserted to exclude Kalmia roots. At low Kalmia cover, reducing the level of belowground competition increased seedling biomass by 134%. However, reducing belowground competition did not increase seedling biomass at the two higher levels of Kalmia cover. It is possible that seedling biomass remained low because of an increased immobilization of N in the organic layer. Furthermore, the proportion of ectomycorrhiza morphotypes differed among seedlings growing under different levels of Kalmia cover. The effect of water-soluble phenols on seedling growth remains uncertain, since we observed a confounding effect of the charcoal treatment on soil microbial biomass and seedling response.