Ledum Groenlandicum Research Articles

Biomass and carbon pool of two bogs in the Experimental Lakes Area, northwestern Ontario

This study was undertaken to estimate the aboveground biomass and carbon pool of plant communities in two bogs: one to be experimentally flooded to simulate a hydroelectric reservoir and the other left unflooded as a reference. The biomass of trees, saplings, and tall shrubs was estimated using allometric regression equations, while that of tree and tall shrub seedlings, low shrubs, herbs, bryophytes, and litter was harvested from 0.25-m2 plots. The eight communities were open or treed in low to high densities with Picea mariana (Mill.) BSP. and sparse Larix laricina (Du Roi) K. Koch. Aboveground community biomass (excluding litter) ranged from 7189 ± 924 (mean ± SE) to 72 909 ± 20 627 kg·ha-1, and litter ranged from 1181 ± 548 to 7664 ± 2848 kg·ha-1. Mean carbon concentration in the plant material analyzed ranged from 430 to 540 mg C·g-1. Carbon concentration of leaves in woody species was higher than in branches and stems. Carbon pool estimates (excluding litter) for the communities ranged from 3140 ± 480 to 35 010 ± 8890 kg C·ha-1. Community carbon per unit area as a percentage of biomass per unit area ranged from 44 to 48%. The available carbon pool (including litter and excluding tree branches and stems) of communities in the experimental bog ranged from 6386 to 9907 kg C·ha-1. Low shrubs, dominated by Chamaedaphne calyculata (L.) Moench in wetter, more open communities and Ledum groenlandicum Oeder in drier, more densely treed communities, composed 34-53% of the available carbon pool. Litter was the largest contributor (33%) to the available carbon pool in the most densely treed community, and bryophytes (mostly Sphagnum angustifolium (C. Jens. ex Russ.) C. Jens. in Tolf and Sphagnum fallax (Klinggr.) Klinggr., 46%) in the sedge community. The available carbon pool in aboveground vegetation of the experimental bog was estimated to be 1.17 × 105 kg C, approximately 12% of the estimated carbon pool in the peat.Key words: biomass, bog, carbon, experimental reservoir.

Podosphaera myrtillina . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Podosphaera myrtillina . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASE: Powdery mildew of plants belonging to the Vacciniaceae only. Infected plants usualy change colour, Ascomata form a brown layer on damaged green parts of host. Development of the disease can by epiphytotic, in which case the crop of berries can be significantly reduced. HOSTS: Arctostaphylos alpina (?), Ledum groenlandicum (?), Vaccinium angustifolium (V. pennsylvanicum), V . × intermedium (V. myrtillus × vitis-idaea), V. membranaceum, V. myrtillus, V. oxycoccos (Oxycoccus palustris, O. quadripetalus), V. uliginosum, V. vitis-idaea . [Type species - Vaccinium myrtillus ] GEOGRAPHICAL DISTRIBUTION: Asia (temperate areas only): Republic of Georgia, Russia (all Russian far east including Kamchatka; west, south and east Siberia including Yakutia). Europe: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Great Britain, Greenland, Hungary, Iceland, Italy, Latvia, Lithuania, Netherlands, Norway, Poland, Rumania, Russia (western and northwestern areas of European part, Moscow oblast'), Slovakia, Sweden, Switzerland, Ukraine, former Yugoslavia. North America: Canada, USA (including Alaska). TRANSMISSION: Probably by wind-dispersed conidia. The rôle of ascospores in disease transmission is unknown, although it has been supposed that they can cause the initial stage of the disease. Infection can also, however, occur from colonies surviving in host buds. In addition, ascomata of Podosphaera myrtillina , especially of var. major , intertwine their appendages to form clusters which are dispersed by rain or wind.

Effects of Ledum groenlandicum amendments on soil characteristics and black spruce seedling growth

The effects of leaves and litter of the boreal forest understory shrub, Ledum groenlandicum, on soil characteristics and black spruce (Picea mariana) seedling growth were investigated. Organic and mineral soils, not previously associated with L. groenlandicum, were amended with leaves and litter of this species. The objectives of the present study were: (i) to determine the changes in soil characteristics after amending with L. groenlandicum, (ii) to determine the quantitative variation in the concentration of water-soluble phenolic allelochemicals in mineral and organic soil layers modified by L. groenlandicum and (iii) to study the growth response of black spruce in soils treated with different L. groenlandicum amendments. The amended organic and mineral soils were analyzed for pH, organic matter, PO4, N, Ba, Cu, Zn, Fe, Mn, Ca, Na, K, Mg, Al and total phenolics equivalence. Results indicate that organic soils amended with L. groenlandicum leaves and litter were significantly different from unamended control soil for most of the chemical characteristics, while amended mineral soil was different from that of unmodified mineral soil for PO4, organic matter, K and total phenolics equivalence. Water-soluble phenolics from L. groenlandicum and changes in nutrient availability are plausible causes of L. groenlandicum interference with black spruce seedling growth.

Patterns of retention and utilization of aerially deposited nitrogen in boreal peatlands

:Nitrogen dynamics were quantified for two years using 15N (as NH4Cl at 3 g N m-2 year-1) in a bog and a rich fen in continental western Canada. After two years, 81–88% of the applied nitrogen was recovered; 98.4-98.7% of the recovered nitrogen occurred in the top 45 cm of the moss-peat layer and 1.3-1.6% occurred in the above ground shrub component. In the bog, 29% was recovered from the top 0–5 cm of Sphagnum fuscum, while in the fen 19% was recovered from this zone in Tomenthypnum nitens. Sphagnum sequestered the applied nitrogen more efficiently than did Tomenthypnum. However, over time Tomenthypnum retained it better in the upper moss layers. Overall, after two years Sphagnum retained 42% and Tomenthypnum 48% in the top 12 cm of the ground layer. The nitrogen of the current year’s moss growth contained 26–28% applied nitrogen (% NDFF) after one season and 19–20% after two seasons. Moss production increased from 4–30% annually over the two year period, while production for Betula pumila in the fen and Ledum groenlandicum in the bog did not increase significantly. Decomposition of S. fuscum in the bog was significantly less than T. nitens in the fen after two years, but no differences were evident after nitrogen additions in either peatlands. We conclude that 1) nearly all nitrogen is immediately sequestered by the moss layer; 2) much of this new nitrogen is found in the actively growing region and moss production increases; 3) shrubs are little affected by the additional nitrogen during the first two years and direct absorption of nitrogen through leaves is unimportant; and 4) newly deposited nitrogen is tightly controlled by the moss layer in both bogs and fens. However retention patterns are different. Subsequent use of nitrogen by vascular plants is determined by nutrient release through decompositional processes deeper in the moss layer.

Trace element chemistry of vegetation applied to mineral exploration in eastern Nova Scotia, Canada

Trace element analysis of conifer tissues demonstrates the application of biogeochemistry to mineral exploration for gold and other metals hosted by lower Paleozoic metasediments in eastern Nova Scotia. At the regional scale, enrichment of up to 170 ppb Au and 72 ppm As in the ash of twigs from balsam fir (Abies balsamea) coincides with known gold districts and major shear zones. These concentrations are approximately 30 times background level. The twig trace element chemistry indicates previously unsuspected Au potential in Carboniferous Horton Group sedimentary rocks, and around the contact aureoles of Devonian granitoids where the twigs are also enriched in Cs (×30), Sb (×3), Rb (×3) and W (×10). Along the Minas Fault, separating the Avalon and Meguma terranes, anomalous groupings of Ba and Cr in twigs suggest exploration potential for base metal (Cu-Pb-Zn) and mafic or ultramafic (Co-Ni-Pt group element) associations. Detailed biogeochemical studies at five till- and/or bog-covered localities near the Beaver Dam gold deposit outline mineralization buried beneath up to 25 m of surficial sediment. An association of Au, As and Cs in the vegetation provides consistent patterns equal to or better than the more erratic geochemical response in soil and till surveys over the same areas. Concentrations of up to 170 ppb Au in the ash of twigs indicate locations suitable for further exploration. The low shrubs Labrador tea (Ledum groenlandicum), leather leaf (Chamaedaphne calyculata) and bog laurel (Kalmia polifolia) were collected from two small boggy areas suspected to overlie gold-bearing bedrock. Typically, these species contain <10 ppb Au in ash. At one site they contained 22 to 36 ppb Au, and at the other they yielded 55 to 85 ppb Au, in association with Cs and weak Co enrichment. In the glaciated terrain of eastern Nova Scotia, biogeochemical exploration is an effective method for delineating metalliferous zones. Multi-site anomalous concentrations of Au and related pathfinder elements occur where subcropping mineralization is covered by till. Regional and prospect-level biogeochemistry can assist exploration by providing valuable data to aid in the discovery of buried or blind mineralization.

Composition of the essential oil of Ledum groenlandicum

The composition of the essential oil of Ledum groenlandicum Retzius was investigated. This oil was obtained by steam distillation (hydrodistillatio

Germacrone defends labrador tea from browsing by snowshoe hares

Labrador tea (Ledum groenlandicum), a slow-growing late successional evergreen, is highly unpalatable to snowshoe hares (Lepus americanus). Germacrone, a sesquiterpene that is the major component of the essential oil ofL. groenlandicum, was shown by bioassay to be a potent antifeedant to hares. Its concentrations in leaves and intemodes of the plant are high enough to defendL. groenlandicum from hares. This chemical defense of Labrador tea from herbivory is consistent with the resource availability theory of antiherbivore defense.

Sulphur gas emissions in the boreal forest: The West Whitecourt case study

The water relations physiology of Pinus contorta × Pinus banksiana and several other important boreal species was studied intensively during 1975–1976 in the vicinity of the West Whitecourt Sulphur Recovery Gas Plant near Whitecourt, Alberta, Canada as part of the West Whitecourt Case Study. Xylem pressure potentials of pine varied from −0.3 MPa to −1.6 MPa and were not noticeably different from pine in areas not receiving S gas emissions such as the Richardson Fire Tower near Fort McMurray, Alberta. Leaf diffusive resistance varied from 2 scm−1 to 60+ s cm−1. The xylem pressure potentials of Picea mariana, Arctostaphylos uva-ursi, and Ledum groenlandicum, were not measurably different from values reported in the literature. Based upon xylem pressure potentials, and leaf diffusive resistances, the water relations of all the species studied in the vicinity of the West Whitecourt Gas Plant did not seem to be measurably affected by S gas emissions. It is concluded that the effects of S gas emission upon photosynthesis are not due to moisture stress.

Biogeochemistry as an aid to exploration for gold, platinum and palladium in the northern forests of Saskatchewan, Canada

Twigs of shrub alders ( Alnus crispa and Alnus rugosa) tend to contain more gold than other common species in the northern forests of Saskatchewan. Alders are not cyanogenic, hence samples can be ashed to preconcentrate gold without loss of the metal as the volatile gold cyanide. Samples from mineralized zones commonly have over 50 ppb Au in the ash of the outermost 50 cm of alder twig. Background values are about 10 ppb Au. In the absence of alder from a given locality, other species may provide useful information on gold in the substrate. Examples are given of surveys using balsam fir ( Abies balsamea), white spruce ( Picea glauca) and black spruce ( Picea mariana). A reconnaissance scale survey in which alder twigs were collected at 2-km intervals has outlined an area, coincident with a major lithostructural domain, within which ashed twigs contained from 20 to 130 ppb Au ( x = 45 ppb Au ). In sharp contrast, alders in a neighbouring area contained less than 10 ppb Au. It appears that this regional approach to biogeochemical sampling in glaciated terrains may provide a quick appraisal of the gold potential of underlying bedrock. Platinum and palladium show a tendency to concentrate in twigs and trunk of black spruce ( Picea mariana) and jack pine ( Pinus banksiana), and in stems of labrador tea ( Ledum groenlandicum). Spruce was sampled close to a worked out nickel-copper deposit that contained 3000 ppb Pt and 6000 ppb Pd. The ashed twigs yielded up to 880 ppb Pt and 1350 ppb Pd, compared to background levels of below 10 ppb Pt and 2 ppb Pd.

Biomass and productivity of the woody strata of forested bogs in northern Minnesota

Biomass and net primary productivity of three forested perched and three forested raised ombrotrophic bogs were determined and compared. The tree stratum was dominated by Picea mariana (Mill.) B.S.P. and the low shrub stratum by Ledum groenlandicum Oeder and Chamaedaphne calyculata (L.) Moench. Based on a modified forest growth and yield model (STEMS), aboveground living biomass of the tree stratum on the perched bogs was declining by about 0.5 t ha−1 year−1 from a base of 100.7 t ha−1, and on the raised bogs it was increasing by 0.2 t ha−1 year−1 on a base of 31.0 t ha−1. Net primary productivity of that stratum was 3.1 and l.0 t ha−1 year−1 on the perched and raised bogs, respectively. Low shrub aboveground productivity, equal to mortality, was 0.4 and 2.0 t ha−1 year−1 on the perched and raised bogs, respectively. This was about 40% of the standing biomass of shrubs in both bog types. Aboveground net primary productivity of woody strata was 3.5 and 3.0 t ha−1 year−1 on the perched and raised bogs, respectively. These data are comparable to earlier estimates of Sphagnum production on the same bogs: 3.8 t ha−1 year−1 on perched bogs and 3.2 t ha−1 year−1 on raised bogs. Vascular herbs contributed an additional 0.2 t ha−1 year−1 to aboveground production on the perched bogs and 0.1 t ha−1 year−1 on the raised bogs. The higher productivity of perched bogs is probably related to slightly higher nutrient status related to their landscape position. The total productivity of all strata of these ombrotrophic sites approaches that of upland sites in the same region.

Determining the availability of traditional wild plant foods: An example of Nuxalk foods, Bella Coola, British Columbia

Forty‐two plant foods known to have been used in the past by native people of the Nuxalk Nation, Bella Coola, British Columbia, Canada, were studied. To estimate the availability of the most prominent plant food resources, field estimates were made using modifications of standard techniques for quantifying plant species. Assessments of accessibility, abundance and frequency of food species were made. In addition, harvesting efficiency of 24 species was determined. Twenty species were selected as being the most readily available food resources, and therefore good candidates for nutritional research and promotion. These included the trees: Populus trichocarpa, Pyrus fusca, Tsuga heterophylla; the shrubs: Amelanchier alnifolia, Ledum groenlandicum, Ribes divaricatum, Rosa nutkana, Rubus idaeus, R. parviflorus, R. spectabilis, Sambucus racemosa, Vaccinium ovalifolium, V. parvifolium, Viburnum edule, and the herbs: Cornus canadensis, Epilobium angustifolium, Heracleum lanatwn, Maianthemum dilatatum, Potentilla pacifica, Trifolium wormskioldii. It was concluded that the variety and quantity of plant food resources of the Nuxalk Nation in the Bella Coola Valley are substantial.

Acid-buffering capacity of foliage from boreal forest species

Buffering capacity to acidity was defined as the microequivalents of H+ required to produce a 5 μeqiv. change of H+ concentration in a homogenate prepared from leaf tissue. The results for six species collected from the southern boreal forest of Saskatchewan, Canada, showed that trembling aspen (Populus trenudoides Michx.) and Labrador tea (Ledum groenlandicum Oeder.), had the highest buffering capacities (379 and 189 μeuiv. H+ ∙ g−1, respectively), while jack pine (Pinus banksiana Lamb.) had the lowest (33 μequiv. H+ ∙ g−1). Tamarack (Larix laricina (Du Roi) K. Koch), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) had intermediate values. Buffering capacity and pH of homogenates for all species showed seasonal fluctuations, with the lowest values occurring in the middle of the growing season. The results suggest that foliage of evergreen conifers, particularly jack pine, is less well buffered against acidic pollution than that of broad-leaved species such as trembling aspen.

The vegetation and water chemistry of four oligotrophic basin mires in northwestern Ontario

Four small oligotrophic basin mires on the Precambrian Shield were quantitatively analyzed for vegetation patterns and surface water and groundwater chemistry. Mean concentrations of ions in the surface waters of all vegetation stands indicate these mires to be characterized by low calcium content (0.6–1.9 mg Ca L−1), low corrected conductivity (12–31 μmho cm−1 (1 mho = 1 S)), and relatively high pH (4.0–5.7). Mire 224 is dominated by Chamaedaphne calyculata, Scheuchzeria palustris, and Carex oligosperma. The surface water mean determinations are Ca, 1.10 ± 0.51 mg L−1; Mg, 0.57 ± 0.2 mg L−1; corrected conductivity, 16.7 ± 4.2 μmho cm−1; and pH 4.37. Abundance patterns of the dominant Carex species can be correlated with pH of the surface water of the mire. Mire 239 is characterized by Smilacina trifolia, Ledum groenlandicum, and Carex trisperma. The mean surface water determinations are Ca, 1.53 ± 0.36 mg L−1; Mg, 0.59 mg L−1; corrected conductivity, 21.2 ± 2.0 μmho cm−1; and pH 4.0. Significant differences in pH, Ca, and Mg occur between the interior and edge portions of this bog. Water chemistry from portions burned in 1974 showed no difference from unburned portions. The vegetation of mire 661 contains a sequence of communities positioned relative to the inflow streams, with a Myrica gale – Alnus rugosa community followed by a zone dominated by Picea mariana then a Larix laricina zone and then by an open Sphagnum papillosum – Menyanthes trifoliata lake edge zone. More ombrotrophic areas are dominated by Sphagnum fuscum. Ca, Mg, and Fe concentrations, pH, and corrected conductivity were reduced through this sequence. Comparison of weekly samples of water entering and leaving this mire in 1981 showed a reduction of Ca, Mg, SO4, NO3 N, alkalinity, and pH.

Effect of Sulfur Dioxide on Woody Boreal Forest Species Grown on Native Soils and Tailings

AbstractA study was carried out on the influence of 15.2 µmol m−3 (0.34 ppm) (Canadian maximum acceptable limit) of SO2 on net CO2 assimilation rate (NAR) and visible symptom development of several boreal forest woody species. Fumigation with SO2 significantly reduced NAR in all species and produced visible symptoms of injury in 2 to 20 d. The decrease in NAR of deciduous species {aspen (Populus tremuloides Michx.), willow (Salix sp.), green alder [Alnus crispa (Ait.) Parsh], and paper birch (Betula papyrifera Marsh)} was significantly more rapid than of conifers { jack pine (Pinus banksiana Lamb.), white spruce [Picea glauca (Moench) Voss], and black spruce [P. mariana (Mill.) BSP]} or an evergreen angiosperm [Labrador tea (Ledum groenlandicum Oeder)] when grown on a fertilized Brunisol. cases did not appear until NAR had decreased considerably. The response of these metabolic and visible responses appeared to be related to differences in S uptake owing in part to higher gas exchange rates for deciduous species than for conifers.Conifers growing in oil sands tailings responded to SO2 with a significantly more rapid decrease in NAR as compared with those growing in the Brunisol. Because both soils were fertilized, nutrient status was ruled out as a cause. It is suggested that the conifers obtained from the railings dike were predisposed to SO2 fumigation by either the presence of toxic material in the tailings sand or their history of exposure to moderate levels of SO2. Sulfur uptake and visible symptom development were not different on tailings as compared with the Brunisol.

Post-pollination callose development in ovules of Rhododendron and Ledum (Ericaceae): zygote special wall.

In Rhododendron spp. and Ledum groenlandicum a callose wall is laid down around the zygote in the first 2 days after fertilization. The periodic acid/Schiff-positive, aniline blue-fluorescence-positive callosic wall is initiated adjacent to the degenerating synergid, extends to cover the entire zygote surface, and remains visible during the initiation of embryogeny as the zygote elongates before the first proembryonal division. Unfertilized ovules show eventual callose deposition in the ovule wall cells during senescence in undeveloped abscising pistils, but show no development of callose within the embryo sac. Possible roles of a zygote special callose wall are discussed.

Natural uranium concentrations of native plants over a low-grade ore body

Plant uranium concentrations generally reflect soil or rock substrate concentrations in upland areas, but they may not in lowland areas where the rhizoids of Sphagnum spp. and the rocks of Ledum groenlandicum may be in direct contact either continuously or on a seasonal basis with the groundwater. This study points out the importance of selecting plant species and collection sites where the true substrate can be well defined and sampled. Sphagnum spp. and Ledum groenlandicum best reflect the substrate uranium concentrations in lowland areas, Umbilicaria spp. and Cladonia spp. in rock outcrop, and Picea mariana and Betula papyrifera in upland locations. The study shows the best plant part to sample is the older tissue such as the stems, twigs, and wood. Since no systematic changes in plant tissue concentrations were found throughout the season, sampling can be carried out anytime. Expression of soil concentrations on an ash weight basis gave a considerably different result than those on a dry weight basis, particularly when comparisons were made between litter-enriched mineral soil and true organic soils. The amount of ash varied among plant organs, species, and taxonomic divisions, and a constant value cannot be used to convert plant ash concentrations to concentrations on a dry weight basis.

Litter Decomposition in a Subarctic Spruce‐Lichen Woodland, Eastern Canada

The litter bag technique was used to examine the decomposition of six litter types (representing Picea mariana, Cladina stellaris, Betula glendulosa, and Ledum groenlandicum) and standard cellulose. The decomposition was measured over a 2—yr period, with tissue samples placed on a recently burnt site and on top of and beneath a lichen mat in a mature spruce—lichen woodland in northern Quebec. Mass losses after 2 yr were between 10 and 60%, with the largest losses occurring in B. glandulosa and L. groenlandicum leaves and the smallest in C. stellaris; 60—90% of the lst—yr mass loss occurs during the winter (September to June). The exponential decay constant k ranged from —0.05 to —0.53. There were few statistically significant differences in decomposition rate among the three sites. Of the chemical constituents analyzed, original concentrations of Ca, carbohydrate, P.K. and N were closely correlated either with the decomposition parameter k or with mass remaining after 1 or 2 yr. Ca, Mg, and k are rapidly lost from the decomposing tissues, except for C. stellaris. All the tissues, except B. glandulosa, showed an accumulation of N. associated with high C:N ratios. The results emphasize the importance of N to this ecosystem, in that it tends to remain immobilized in the litter, at least over the first 2 yr.

Anomodon minor (Musci: Leskeaceae) in North America

Anomodon minor (Hedw.) Furnr. is reported from a disjunct locality in northeastern Alberta, Canada. Its occurrence in eastern North America, with disjunct populations in the south- western United States and Mexico, is mapped. One of us recently collected Anomodon minor in northeastern Alberta along the Clearwater River floodplain at 56042'N, 110*08'W (Lee, June 30, 1983--ALTA, CANM, UBC). The species occurs there on sheltered clifffaces ofthe Middle Devonian Methy formation outcrops, which are hard, buff-colored, porous dolomites. The general vegetation of the area is dominated by scrubby, open Populus tremuloides Michx. with Betula papyrifera Marsh., Pinus bank- siana Lamb. and Picea glauca (Moench) Voss in- termixed in the canopy. Understory vegetation is highly variable within short distances, reflecting the rugged topography. Moist sheltered draws have 100% plant cover dominated by Linnaea borealis var. americana (Forbes) Rehd., Mitella nuda L., Ledum groenlandicum Oeder and by feather moss- es, particularly Hylocomium splendens (Hedw.) B.S.G. The drier, exposed summits of the outcrops have only 30% plant cover dominated by Juniperus communis L., Elymus innovatus Beal, Ditrichum flexicaule (Schwaegr.) Hampe and Pleurozium schreberi (Brid.) Mitt. Bryophytes commonly found on the cliff faces and crevices include Hypnum cu- pressiforme Hedw., Encalypta procera Bruch, Thui- dium abietinum (Hedw.) B.S.G., Rhytidium rugo- sum (Hedw.) Kindb., Ditrichum flexicaule

Modelling geographic variation in the timing of shoot extension by ericaceous shrubs

The seasonal timing of shoot extension by three ericaceous shrubs (Ledum groenlandicum, Chamaedaphne calyculata, and Kalmia polifolia) was monitored at eight peat bogs along an 800-km latitudinal transect through Ontario, Canada, and at a transplant garden containing plants from four of the peat bogs. The timing of shoot extension varied among plants from different locations, both in the transplant garden and in the field. A regression model containing two independent variables (heat units (i.e., degree-days) and either the average annual degree-day total for a plant's geographic origin or the average frost-free period) could account for 95 to 99% of the seasonal plus intersite variation in shoot extension recorded in the transplant garden. The seasonal pattern of shoot extension predicted for each of the eight peat bogs with the regression model was close to the observed pattern in most cases. The average difference between predicted and observed percentages of shoot extension ranged from 4% for L. groenlandicum to 7% for K. polifolia.

Carbon Allocation to Antiherbivore Compounds in a Deciduous and an Evergreen Subarctic Shrub Species

Seasonal patterns of 14C-photosynthate allocation to secondary chemicals in Betula glandulosa Michx. and Ledum groenlandicum Oeder from northern Quebec were analysed in the context of resource utilization in deciduous and evergreen leaves. A sequential extraction procedure was used to separate volatile compounds, total phenolics, alkaloids and organic acids from '4C-labelled leaf tissues. Sugar, nitrogen and cell wall constituent concentrations were measured as indicators of leaf nutritive quality and hence susceptibility to herbivore attack. Both species allocated the greatest proportion of current photosynthate to total phenolics early in the season when leaf susceptibility was highest. Lignin contents were also high at that time. During the growth period carbon allocation to total phenolics decreased while alkaloids and volatile compounds peaked. This indicated a competitive interaction among metabolic pathways involved in growth and defensive chemical production. Allocation to the organic acid fraction was highest early in the season. While both species utilized quantitative and qualitative defenses, the evergreen leaves allocated relatively more carbon to total phenolics while the deciduous leaves had a greater emphasis on alkaloids and organic acids. The evergreen leaves also allocated current photosynthate to volatile compounds, but only in their first season. The emphasis on total phenolics decreased with leaf age in the evergreen species, but the levels of allocation to alkaloids and organic acids were maintained. The results supported the hypotheses (1) that defensive systems exist in the leaves of the species studied, and (2) that the carbon cost of defense is directly related to the plants' sensitivity to leaf loss, both between species and among leaf age classes.