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Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown in the greenhouse in a sterilized mixture of forest soil and vermiculite, which had been inoculated with root fragments from one of six different ectomycorrhizal under story plant species (Arctostaphylos uva-ursi (L.) Spreng, P. menziessi, Salix bebbiana Bebb, Alnus viridis subsp. sinuata (Regel) Ä. Löve & and D. Löve (alder), Betula papyrifera Marsh. (paper birch), Populus tremuloides Michx.) and arbuscular mycorrhizal Calamagrostis rubescens Buckl. (pinegrass) sampled from a dry Douglas-fir forest in the southern interior of British Columbia. The overall objective of the present study was to investigate the inoculum potential of these ectomycorrhizal roots for colonizing Douglas-fir seedlings. A total of seven ectomycorrhizal morphotypes formed on the bioassay seedlings, which were colonized by all treatments except the control. Seedlings growing in soil inoculated with root fragments of Douglas-fir, Arctostaphylos, and paper birch had greater ectomycorrhizal richness and a higher percentage of colonized fine roots relative to the pinegrass and alder treatments. The community of ectomycorrhizal fungi that colonized the bioassay seedlings differed from that associated with some of the same refuge plants assessed in a previously reported field-based study at this site. Different ectomy corrhizal fungal colonization strategies and the retention of refuge plants are discussed in relation to the colonization of outplanted seedlings following clearcutting.Key words: ectomycorrhizae, refuge plants, inoculum potential, soil bioassay, Pseudotsuga menziesii.

In wet soils, nitrogen-fixing root nodules are subjected to elevated CO2. Only a few studies have examined the effect of elevated CO2 on nitrogenase activity, and the results have been mixed. We examined intact black alder (Alnus glutinosa (L.) Gaertn.) and sweet gale (Myrica gale L.) seedlings and field-collected speckled alder (Alnus incana ssp. rugosa (Du Roi) Claus.) nodules to clarify the effects of elevated CO2. Nitrogenase activity was measured via acetylene reduction in an open, flow-through system. We found that repeated measurements of the peak rate of nitrogenase activity, the only reliable measure of nitrogenase activity, could be made on the same plant via 150-s exposures to acetylene separated by 20 min without acetylene. Our results for elevated CO2 consistently showed that it had little effect on nitrogenase activity at low concentrations and increasingly inhibited nitrogenase activity as the CO2 concentration increased. In black alder, 0.5 kPa CO2 had little effect, whereas 3.0 kPa CO2 reduced nitrogenase activity 31–35%. Sweet gale, was less sensitive to elevated CO2 and was unaffected by 1.5 kPa CO2. Black alder grown with the roots, but not the shoots, in 1.3 kPa CO2 showed only minimal acclimation to elevated CO2.Key words: acetylene reduction technique, actinorhizal plants, Alnus, carbon dioxide, Myrica gale, nitrogen fixation.

Red alder (Alnus rubra Bong.) is a nitrogen-fixing woody plant that is common on wetland sites and tolerates flooding through a variety of induced morphological and physiological changes. Among these changes are the formation of hypertrophied nodule lenticels and the subsequent full restoration of nitrogenase activity after 50 days of flooding. The objective of this study was to examine fine structural changes within red alder nodules during lenticel development that correspond to changes in nitrogenase activity during a 50-day experimental flood. Nodulated seedlings of red alder were grown under greenhouse conditions and then exposed to root flooding for 1, 20, 35, or 50 days. At each harvest, estimates of nitrogenase activity were made via acetylene reduction, and nodule samples were taken for light-microscope examination. Only after 50 days of flooding did red alder show restoration of nitrogenase to pretreatment levels. At this time, Frankia vesicles were found to be directly adjacent to developing lenticel tissue and large intercellular spaces. Intercellular space within the nodule increased from 0.6% in nonflooded tissue to 5.7% after 50 days of flooding. Our results demonstrate the sensitivity of the nitrogenase enzyme to low oxygen soil conditions and indicate that substantial morphological change within the nodule must occur before red alder can regain the capacity to fix nitrogen under flooded conditions.Key words: Alnus rubra, Frankia, waterlogged, biological nitrogen fixation, hypertrophied lenticels, intercellular space.

Although most vascular plants have symbiotic relationships with soil microbes, and there is an extensive theoretical literature on the evolution of mutualism, there has been little experimental examination of the evolution of mutualism between plants and their microbial symbionts. We inoculated red alder (Alnus rubra Bong.) seedlings from three high- and three low-elevation populations with crushed nodule suspensions containing the nitrogen fixing bacterium Frankia from either the parent trees (familiar strains) or the other plant population sampled within the parent watershed (unfamiliar strains). The inoculated seedlings were planted on three high- and three low-elevation sites. Growth was monitored over the second and third year following planting, after which the whole plants were harvested. The proportion of nitrogen derived from fixation was estimated from the ratio of stable nitrogen isotopes in the harvested leaves. On low-elevation sites, which had high soil nitrogen, plants with familiar Frankia strains were half the size and derived less fixed nitrogen from their symbionts compared with plants inoculated with unfamiliar Frankia strains. On high-elevation sites, which had low soil nitrogen, the type of inoculum had little effect on plant performance, although plants with familiar inoculum were consistently larger than plants with unfamiliar inoculum. These results suggest that the degree of mutualism in this symbiosis depends on environmental conditions and may decrease with time.Key words: coevolution, Frankia, Alnus rubra, mutualism, nitrogen fixation, symbiosis.

The time course of acetylene reduction was examined in field nodules of speckled alder (Alnus incana ssp. rugosa (Du Roi) Claus.) and sweet gale (Myrica gale L.) with an open flow-through system. When detached speckled alder nodules were measured in the laboratory, there was an initial peak rate of nitrogenase activity between 2 and 3 min followed by pronounced declines to 50% of the peak rate (early summer) and 66% (late summer) at 9 min, after which there was little further change. Speckled alder nodules measured in the field while still attached to the plant also had a peak rate between 2 and 3 min. Most sweet gale nodules had a peak rate at 2–3 min and a sharp decline to 27% at 21 min followed by a partial recovery to 49% at 60 min. The time courses of field nodules of speckled alder and sweet gale were comparable with those of intact, growth chamber grown seedlings. The initial peak rate is the most accurate measure of nitrogenase activity and the only reliable way to measure this is with an open, flow-through system. We describe a simple, inexpensive, flow-through system for use in the field. Key words: acetylene-induced decline, Alnus incana ssp. rugosa, actinorhizal plants, Myrica gale, nitrogen fixation, nitrogenase activity.

Mycorrhizal fungi associated with plant species may change as vegetation develops following disturbance. The objectives of this study were to compare ectomycorrhizae through a chronosequence on deglaciated land from bare mineral soil to mature forest and to determine time required for mycorrhizal formation on natural seedlings. A chronosequence that formed as Exit Glacier retreated enabled us to document changes in mycorrhizae on existing woody plants, including Populus balsamifera ssp. trichocarpa (Torr. & Gray) Hult, (black cottonwood) that dominates the early stages, Alnus sinuata (Regel) Rydb. (Sitka alder) that has few ectomycorrhizal fungal associates, and Picea sitchensis (Bong.) Carr. (Sitka spruce) that typifies late successional stages. Some seedlings of Populus balsamifera became ectomycorrhizal within 3 weeks of germination but most took longer. Although a dark type without clamp connections dominated willows in the second and third stage, it was not a dominant in the first stage and was rare on 1st year seedlings. Ectomycorrhizal types differed among successional stages for Populus balsamifera. Diversity increased from early successional stages to later stages, mostly from an increase in evenness rather than richness. Arbuscular mycorrhizae were not found on any woody plants, although a few herbaceous plants had low infection percentages. Keywords: ectomycorrhizae, chronosequence, Populus, Alnus, Picea, Salix.

The transition from alder (Alnus tenuifolia) to balsam poplar (Populus balsamifera) is a critical turning point in primary succession on river floodplains in interior Alaska. Associated with the change in plant species are large changes in N cycling. N-fixation and nitrification decrease and the system becomes N-limited, with NH4+ dominating the inorganic N pool. Balsam poplar leaves contain large quantities of tannins and low molecular weight phenolic compounds. We evaluated the effect of these compounds on microbial respiration and N cycling in laboratory assays on soils from an alder-dominated site. Plant compounds were purified and applied to silica gel as an inert carrier. Both tannins and phenolics caused net N-immobilization over a 30-day assay. However, tannins inhibited respiration while phenolics stimulated it. There were no specific effects on nitrification. Thus, tannins acted as a general microbial inhibitor, while phenolics acted as a growth substrate. By inhibiting mineralization while stimulating immobilization, poplar secondary compounds may reduce soil N-availability during the transition betwen alder and poplar stages in succession. Keywords: respiration, mineralization, tannins, secondary chemicals, succession, plant–microbe interactions.

The foliar phenology of potted 1-year-old seedlings of alder (Alnus hirsuta Turcz.), maple (Acer mono Maxim.), and birch (Betula platyphylla Sukatch. var. japonica Hara) was observed from May to September in eight growth environments: factorial combinations of temperatures (light:dark, 30:20 °C and 26:16 °C), CO2 level (70 and 36 Pa), and nutrient regime (high versus low levels of fertilization). Seedlings grown at high fertility always had more leaves, and under high CO2, shed leaves slightly later than seedlings grown at low fertility. Except for maple, production of newly formed shoots and leaves was accelerated by high CO2. In maple, high CO2 only increased the number of flushes of the leader shoot. Alder and birch accelerated sylleptic shoot and leaf production at high CO2 in fertile conditions. The production of new leaves by alder grown at high CO2 and low fertility was almost the same as that grown under normal CO2, at high fertility. At high CO2, the timing of winter bud formation of monopodial alder and maple was delayed, while that of sympodial birch was almost the same as at ambient CO2. Key words: foliar phenology, elevated atmospheric CO2 and temperature, monopodial versus sympodial growth, nutrient levels, winter bud formation, global change.

Spring and early summer flood is one of the main factors affecting the dynamics of black ash (Fraxinus nigra Marsh.) stands growing on lake floodplains in the boreal forest. The effect of flooding on the vegetation was studied in five stands on the shore of Lake Duparquet in Abitibi, northwestern Quebec. Divisive hierarchical classification analysis (Twinspan) revealed the existence of four different vegetation types: (i) black ash – speckled alder (Alnus rugosa) – bog willow (Salix pedicellaris), (ii) black ash – balsam poplar (Populus balsamifera) – ostrich fern (Matteuccia struthiopteris), (iii) black ash – pussy willow (Salix discolor) – sensitive fern (Onoclea sensibilis), and (iv) black ash – speckled alder – sensitive fern. Detrended correspondance analysis (Decorana) shows that elevation and drainage are the main factors affecting plant distribution and dynamics. Geomorphology also plays a major role in the way each stand responds to flooding. For each of the vegetation types studied, black ash shows a particular regeneration pattern and sexual regeneration tends to become less frequent with increasing exposure to flooding. Finally, the strong sexual regeneration and the youth of the populations found in the most elevated sites could be related to a possible alteration of the flood regime. Key words: Fraxinus nigra Marsh., flooding, boreal forest, floodplain, ecological gradiant, regeneration.

N2 fixation by grey alder, Alnus incana (L.) Moench, was studied in the field during two growing seasons in northern Sweden. Alders were planted in a nitrogen-poor soil. Each alder had its root system enclosed in an open-ended cylinder that was closed with a gas-tight lid around the stem base to serve as cuvette during nitrogenase activity (acetylene reducing activity) measurements. To follow the seasonal variation, nitrogenase activity was measured at noon on 15 occasions for each alder in 1987 and on 15 occasions in 1988. Diurnal variation in nitrogenase activity was studied at six occasions, but no obvious pattern in the diurnal variation was found. Nitrogenase activity began shortly after leaf emergence at the very end of May, increased in June, stayed high although with some variation through July and August, declined during September, and was zero in early October. Cumulative nitrogenase activity over the season was converted to cumulative N2 fixation after determination of molar ratio nitrogenase activity to N2 fixation. This conversion was facilitated as the Frankia chosen as symbiont was lacking hydrogenase activity. Control experiments showed that the introduced symbiont was the only infective Frankia in the soil. N2 fixation was estimated to be 0.23 and 2.83 g N/(alder∙year) in the 1st and 2nd year, respectively. Despite its young age, A. incana was apparently capable of high N2 fixation rates at the high latitude studied. Key words: Alnus incana, hydrogenase, intact plants, N2 fixation, seasonal variation, spreading of Frankia.

Fixation of atmospheric N2 may provide an advantage to woody plants in N-limited environments, but may also alter their resistance to herbivory. Studies in adjacent plantings of three North American shrub alders (Alnus spp.) and three Eurasian tree alders showed significant species differences in susceptibility to a leaf-mining sawfly (Fenusa dohrnii) and in response to inoculation with a N2-fixing actinomycete (Frankia). During the first 5 years, woody biomass production ranged from 0.3 t∙ha−1∙year−1 in Alnus viridis ssp. sinuata (Sitka alder) to 8.3 t∙ha−1∙year−1 in Alnus incana ssp. incana (grey alder). Grey alder and another tree species (Alnus japonica) were attacked infrequently and suffered little sawfly damage except in plots with poor growth. The tree species Alnus glutinosa (black alder) was attacked frequently, and sawfly damage was greatest in plots with the best growth. The shrub species Alnus viridis ssp. crispa (green alder) was also attacked frequently but was highly resistant to larval feeding. Frequently attacked species showed greater damage in the lower portion of the crown. Frankia inoculation increased green alder biomass by 87% but had no significant effect on grey alder or black alder. The concept of a growth-defense trade-off does not fully explain the interactions between Alnus spp. and F. dohrnii. Key words: Alnus, Fenusa dohrnii, Frankia, biomass production, plant–herbivore interactions, leaf miner.

Critical ecological research on belowground ecosystems has often been impeded because of the inability to adequately recognize ectomycorrhizal relationships, especially the abundance, diversity, and distribution of the fungus component, and the specificity of particular fungus–host combinations. Red alder, with its high degree of host specificity and paucity of fungal symbionts, provides an ideal model for studying these attributes. Eleven morphologically recognizable types of ectomycorrhizae were characterized from field-collected root material, greenhouse soil bioassays, and laboratory syntheses. Most mycobionts were basidiomycetes, as evidenced by abundant clamp connections present in the mantle and extramatrical hyphae. Seven mycobionts identified to species included Alpova diplophloeus, Thelephora terrestris, Lactarius obscuratus, Cortinarius bibulus, Laccaria laccata, Hebeloma crustuliniforme, and Paxillus involutus. Many of the ectomycorrhizae collected in the field appeared to have more than one mycobiont present in the mantle. Root tips could generally be categorized into either flexuous or succulent morphological types. The flexuous types were long, thin, indeterminate in growth, with an acute root apex, and the mantle and Hartig net in longitudinal section were not well formed near the root apex. The succulent types were short, thick, determinate in growth, with a rounded root apex, and the mantle and Hartig net in longitudinal section were well formed near the root apex. Additional characteristics important in distinguishing among red alder ectomycorrhizal types included color, extent of extramatrical hyphae development, mantle surface characteristics, and selected microchemical reactions. Mantle thickness was highly variable and not useful in characterization. Hartig net development was shallow, and regardless of mycorrhizal origin, rarely extended beyond one epidermal cell layer. Key words: ectomycorrhizae, Alnus, characterization, ecology, belowground.

A study was designed to isolate potentially pathogenic, endophytic fungi of red alder (Alnus rubra). Apparently healthy leaves and 2- to 3-year-old twigs were collected at three and eight sites, respectively, surface sterilized, cut into small pieces, and incubated on 2% malt extract agar. Ninety percent of the leaves and more than 80% of the twigs were colonized by endophytic fungi; 40 different fungi were isolated and identified. Fungi previously recorded as plant pathogens dominated the endophyte community of leaves (Gnomonia setacea, Gnomoniella tubaeformis, and Septoria alni) but were only minor components of the fungal population of twigs (Melanconis alni and a Nectria species). Abundance of each fungus species and the species composition depended on the plant organ sampled and collection site. In twigs, three main types of endophyte associations occurred among sites: the first was dominated by the unidentified "Black Mycelium 2," the second by Phomopsis sp. 2, and the third by Ophiovalsa suffusa, Pezicula livida, and Phloeosporella sp. The endophyte community of leaves was dominated by G. setacea except at one site where G. tubaeformis was the predominant fungus. Key words: endophytic fungi, fungal community, Alnus rubra, mycoherbicide.

Four-year-old plantation-grown autumn olive (Elaeagnus umbellata Thunb.) and black alder (Alnus glutinosa L.) trees were analyzed for gross heat value, ash, alcohol-benzene extractives, hot-water extractives, 1% NaOH extractives, lignin, and pentosan. These plantations were established on marginal land that was not suitable for food production in Illinois. For comparison purpose, lumber from 60-year-old black alder trees was also analyzed. Test results indicated that the planting sites (bottomland vs. upland) factor did not affect the chemical composition of both trees. The main factor, species, was significant in determining various chemical properties. Black alder had higher average alcohol-benzene extractives, 1% NaOH extractives, pentosan, ash, and gross heat content than autumn olive. Autumn olive had higher hot-water extractives, lignin, holocellulose, and alpha-cellulose content than black alder. The commercial alder lumber had less chemical extractives but was higher in alpha-cellulose than the 4-...

Small numbers of cluster roots were found on older roots of Alnus incana ssp. rugosa (speckled alder) shrubs in the field at 2 of 11 sites. Cluster roots also formed infrequently in speckled alder grown hydroponically in complete nutrient solution. No cluster roots formed in solutions lacking P or Fe. Small numbers of cluster roots also formed in Alnus glutinosa grown hydroponically in the presence of P but not in its absence. In contrast, Alnus rubra produced small numbers of cluster roots in the absence of P but not in its presence. No cluster roots formed in Alnus viridis ssp. crispa. Cluster roots are probably not important for nutrient uptake in speckled alder because they form infrequently both in the field and in hydroponic culture. Keywords: Alnus incana ssp. rugosa, Alnus glutinosa, Alnus rubra, Alnus viridis ssp. crispa, cluster roots, proteoid roots.

The morphology and structure of nodules on the exotic tree alder Alnus japonica (Thunb.) Steud. inoculated with the North American Frankia strain HFPArI3 were examined under different nutrient conditions. Seedlings were subjected to a nitrogen, phosphorus, or iron stress treatment using the Ingestad nutrient addition technique which generally produced a decrease in the length of healthy endophytic vesicle cluster zones. External nodule morphology varied according to treatment, with thicker nodules developing under "good" nutrient conditions. Nodule meristems showed apparent apical dominance under conditions of nutrient stress. Increased additions of inorganic nitrogen reduced the levels of nitrogen fixation and increased cortical cell size but reduced the numbers of endopytic vesicles per unit area. High nitrogen fixation levels were accompanied by the formation of numerous large mitochondria in nodule pericycle cells.

We measured alder plants (Alnus viridis ssp. crispa (Aiton) Turrill) in stands on 11 sites on the Seward Peninsula. Of the plants measured in detail, 70% had multiple stems (largest difference in stem age on a plant was 67 years), 54% had small epicormic shoots, and 59% had partially prostrate stems that could layer. The oldest stems were 35–114 years on alpine tundra, 47–48 years on river cuts, 36 years on moist tundra, and 16–33 years on floodplain. This species appeared to be reproducing by means of seedlings on 8 of 11 sites. Alder pollen percentages in surface samples from seven small ponds were negatively correlated with distance to alder stands. Pollen and 14C analysis of sediments from a pond near one sample stand showed that alder pollen percentages had decreased over the past 3600 years, but that alder had persisted in the area during this period. Estimates of potential plant age, dependent on assumptions about the production and survival of new stems, ranged from 100 years to unlimited age. The maximum age of stands is at least 100–200 years, but could be up to the 3600 years shown by a continuous pollen record and 14C analysis.

Flowering, seed production, and germination of green alder (Alnus viridis ssp. crispa (Aiton) Turrill) were studied in populations north of Lake Superior. Anthesis and fertilization took place from mid-May to early June. Aboutone-third of the lateral buds contained female catkins, and an average of 60% of these catkins were fertilized and bore some seed. A high percentage of seed had abnormal, nonviable embryos. There was wide variation in flowering and seed characteristics among clumps of alder. Reproductive features of individual clumps were not correlated from year to year, suggesting an alternate bearing pattern in which some clumps were productive in any given year. Annual seed rain in individual understory alder stands varied from 0.14 to 2.40 million per hectare. At dispersal seeds exhibited conditional dormancy, which allowed germination at higher temperatures under a long photoperiod. Capacity for germination under a wider range of environments was facilitated by stratification.

Biomass, net primary production and nitrogen fixation rates were measured in a 5-year-old Sitka alder (Alnus sinuata (Regel) Rydb.) stand. Acetylene reduction assays yielded a nitrogen fixation estimate of 35 kg N ha−1 year−1. The biomass of leaves, stems, roots, and nodules was 13 720 kg ha−1 and aboveground net primary production was 6000 kg ha−1 year−1.

The influence of nitrogen reserves on leaf formation of 5- to 6-year-old plants of Alnus glutinosa (L.) Gaertn. was investigated using a 15N labelling method. Nitrogen reserves were derived essentially from the root system and along with N fixation by Frankia, supported the growth of the young leaves. The reserves represent 10% of the total nitrogen in the leaves at the end of the growing period under natural or environmentally controlled conditions. The percentage of fixed nitrogen in alder leaves was estimated to be 87% taking into account the nitrogen reserves and using the isotopic comparison with a nonfixing plant (Populus alba L.). Several conditions requiring the use of 15N methods to estimate the symbiotic nitrogen fixation by Frankia were formulated. The selection of samples for analysis must be from the most recently formed leaves at the end of the growing season to avoid the influence of nitrogenous reserves. Key words: nitrogen reserves, Alnus glutinosa, Populus alba, Frankia, 15N fixation.

Two clones of Alnus glutinosa plantlets propagated in vitro were inoculated, under axenic conditions, with eight different isolates of Frankia originating from different provenances and representing both type-N and type-P strains. All the plants inoculated formed typical and effective actinorhizae. The nodulated root systems were tested for the presence of microbial contaminants on different culture media. Typical Frankia colonies, growing on the root pieces incubated in the culture media, were subcultured and reinoculated on alder seedlings grown in plastic growth pouches. The results demonstrated that Frankia can induce a typical and effective nodulation on axenic Alnus glutinosa host plants without the help of any "microbial helper".

Fruiting bodies and forest floor samples were collected and analyzed for N, P, K, Ca, Mg, Mn, and Na content in red alder, Douglas-fir, western hemlock, and Pacific silver fir ecosystems in western Washington. Different genera and species of fungi showed wide variation in the capability of concentrating nutrients within their fruiting bodies. Ranges of nutrient content for fruiting bodies were 0.66–11.27% N, 0.04–2.39% P, 7 – 32 080 ppm Ca, 2975 – 57 404 ppm K, 10–7096 ppm Mg, 3–1727 ppm Mn, 15–3975 ppm Fe, 18–6763 ppm Na, and 15–278 ppm Zn. Nitrogen, P, and K were concentrated in significantly higher levels in fruiting bodies versus the forest floor in all ecosystems. Nitrogen and K were concentrated at levels higher than 1% while P, Ca, Mg, Mn, and Na were concentrated at levels less than 1% of the dry weight of the fruiting bodies. Calcium was not concentrated by fungi in sporocarps, except for Armillariella mellea rhizomorphs (3.2% on dry weight basis). Lignicolous fungi were lower in N and K than nonlignicolous fungi.

Cultures of 28 ectomycorrhizal fungi were tested in pure culture syntheses for mycorrhiza formation with red alder. Only 4 of the 28 fungi tested formed characteristic ectomycorrhizae: Alpova diplophloeus, Paxillus involutus, Aslraeus pteridis, and Scleroderma hypogaeum. These mycorrhizae are briefly described, and the specialization of alder mycorrhizae is discussed.

Procedures for estimating the diversity of Frankia isolates are described. Forty-three alder isolates were separated into six groups by comparing protein patterns obtained during sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS–PAGE) of whole-cell lysates. Thirty-five of the strains comprised group A and were indistinguishable from one another. Four strains were quite similar to a Comptonia peregrina isolate (CpI1) and were included in group C. Group D had two members and groups B, E, and F each had one member. The groupings were confirmed by hyphal morphology, colony appearance, and carbon source utilization patterns.

During two vegetative seasons (1977, 1978), Alnus viridis Chaix root nodules were incubated in the field and assayed for nitrogen fixing activity by acetylene reduction method. In green alder the nitrogenase activity took place with the first opening of buds (June); maximum values were attained in July–August; the activity decreased steadily until leaf fall, and then ceased. Diurnal fluctuations in acetylene reducing activity were observed, the 1400-hour values were twice those of 1000 hours. The optimal temperature for nitrogenase activity was below 20 °C; this fact would be in relation with better adaptation of Alnus viridis to cold climate. The nodular biomass being only 40 kg/ha, the nitrogen fixed during the vegetative season (mid-June to mid-October) was only about 8 kg/ha. Symbiotic fixation accounted for only 10% of the nitrogen requirements of green alder.

A method for the inoculation of Douglas fir roots with Poria weirii using Douglas fir, alder, maple, and oak wood for preparing the inoculum is described. When the deciduous wood was used as the food base on which the fungus was grown, a higher percentage of infection was achieved than when either Douglas fir stem or roots were used. Six months was sufficient time for the fungus to become well established on the bark surface; penetration of healthy bark occurred in 12 months. Spread of the fungus to adjacent roots at points of root contact was noted. Growth of mycelium on the bark surface was usually well in advance of infection in the wood. Poria mycelium continued to grow vigorously during the fall and winter months of the study period.

Samples of surficial lake sediment and of moss polsters from 39 sites in the forest-tundra transitional area immediately east of the Mackenzie Delta, Northwest Territories, were investigated palynologically. Lake sediment samples within the forest and tundra regional vegetation zones are constant in pollen frequencies, but forest–tundra sites are very variable. Forest site spectra are composed of just over 50% arboreal types (spruce, 25–30%; birch, 30%), with 30–40% alder pollen. Tundra spectra have 60–70% non-arboreal types, and 10–15% each of alder and spruce. Forest–tundra values are variable, generally lying between the forest and tundra proportions. Polster samples show as much variability within as between regions, because of local effects. Polster samples indicate local community composition with the regional pollen rain variably masked by the local elements.

The comparative growth rates and wood destructive ability of two isolates of Tomes fomentarius (Fries) Kickx. were investigated under laboratory conditions. The pure cultures were obtained from 2-year-old fruiting bodies, growing on stumps of birch (Betula verrucosa Ehrh.) and spruce (Picea excelsa L.) trees situated in the same locality. Comparing the rates of growth of these isolates, on beer-must agar, it was found that isolates from spruce stumps grew faster and covered the entire surface of the medium in 11 days, whereas isolates from birch overgrew the same area in 16 days. The wood-destroying ability of spruce isolates was greater on pine, spruce, and oak wood blocks, whereas birch isolates were more destructive to birch, beech, aspen, alder, linden, and maple. The macro-and micro-scopic characteristics of mycelial mats of both isolates, as well as the fruiting bodies, revealed no difference between them.

The effect of soil moisture and the related effect of some soil-inhabiting microorganisms on the spread through soil of the root-rotting Basidiomycete Coniophora puteana were studied. A soil moisture level of 20%–25% saturation was satisfactory for the growth of C. puteana in non-sterile soil. The fungus was able to grow out from a small alder disc inoculum in the center of a petri dish and invade alder discs at the periphery of the dish. At 50% saturation and higher C. puteana was unable to grow out into the soil. In autoclaved soil the optimum moisture level for the growth of C. puteana was between 75% and 100% saturation.Small amounts of non-sterile soil were added to autoclaved soil at different moisture levels, with an effect on the growth of C. puteana similar to that of completely non-sterile soil. Trichoderma viride, a known antibiotic producer, was inoculated into autoclaved soil and produced a greater inhibition of C. puteana in the wetter treatments than in drier ones. The inhibitory effect of Acti-dione (cycloheximide), an antifungal antibiotic, was examined in autoclaved soil. The same concentration of antibiotic resulted in a greater inhibition of the growth of C. puteana at the higher moisture levels than at the lower ones. Some implications of the findings are discussed.

More rapid growth by red alder than by coastal conifer species may be explained by alder's greater foliage surface per unit foliage weight, greater total foliage area per seedling, and higher photosynthetic rate at high light intensities. Net photosynthetic rates per unit foliage area were similar for red alder and the three conifers up to saturating light intensity for the conifers. Relative weight of photosynthetic and nonphotosynthetic tissue was also similar for the four species. Average maximum photosynthetic rates measured for these conifers are comparable to reported rates for woody broad-leaved species.

Quantitative data from solution cultures of Alnus rugosa are presented which indicate facultative independence of this species regarding combined nitrogen supply and its close similarity to A. glutinosa in efficiency of N-fixation and physiology of nodule symbiosis.Volume–weight measurements and chemical analyses are given for soils and soil – surface organic matter in stands representative of succession involving nodulated A. rugosa, confirming that this species is capable of contributing greatly to nitrogen levels of the soil. Total seasonal litter-fall from woody species in several stands was collected and analyzed for nitrogen. Annual amounts of litter-N returning to the ground appear to be substantially greater under alder and alder–forest phases than under those dominated by Salix and Salix–forest vegetation. On favorable sites, soil nitrogen may accumulate under Alnus rugosa thickets at rates in excess of 150 lb/acre per year.However, no excess nitrogen accumulation was found in sandy soil supporting the Alnus shrub phase of a dry upland "old-field" succession and an explanation for this has been advanced.The past and present ecological position of Alnus species in northeastern North America is related to their capacity to fix nitrogen.

The occurrence and distribution of symbiotic cauloplane organisms on dormant cuttings of 1- to 2-year-old stems of alder, black cottonwood, maple, and willow were determined from tissue samples removed to 2% malt extract and nutrient broth agars, and from scanning electron micrographs of the bark surfaces. Fungal and bacterial symbionts were found to be confined to the bark surfaces, where their occurrence was related to the surface topography. Inner bark, wood, and pith were virtually aseptic.

Root rot caused by Poria weirii Murr. occurred when healthy roots of Douglas fir came into contact with inoculum in infected roots of the previous stand. Mycelium grew ectotrophically on the bark of the Douglas fir roots, frequently well in advance of growth in the wood, and penetrated to living tissues directly through sound as well as injured bark. Spread of the disease to adjacent trees took place where healthy and diseased roots were in contact, the mycelium apparently spreading to only a very limited extent through natural soil. It was shown that mycelium could invade roots of trees felled for at least 12 months and Douglas fir heartwood that had been buried in soil for at least 12 months. Viable Poria mycelium was isolated from infected roots as small as 2 cm in diameter 11 years after the trees had been cut. While Douglas fir and western hemlock appeared to be quite susceptible to infection, western red cedar, red alder, and bigleaf maple showed considerable resistance.

Typical cankers with stromata were produced when aspen were inoculated with isolates of Hypoxylon mammatum (H. pruinatum) from aspen, but isolates from alder and willow were incapable of producing typical cankers on aspen. Isolates from willow produced cankers initially, but these were eventually callused over. Isolates from alder and aspen were not able to incite cankers on alder. Dimensions of the perithecia and ascospores of the fungus on aspen are not sufficiently different from those on birch, willow, and alder to justify maintaining H. pruinatum as a species separate from H. mammatum.