Bare-root Forest Nurseries Research Articles

Ectomycorrhizal Fungal Assemblages of Nursery-Grown Scots Pine are Influenced by Age of the Seedlings

Scots pine (Pinus sylvestris L.) is the most widely distributed pine species in Europe and is relevant in terms of planted areas and harvest yields. Therefore, each year the demand for planting stock of Scots pine is exceedingly high, and large quantities of seedlings are produced annually throughout Europe to carry out reforestation and afforestation programs. Abundant and diverse ectomycorrhizal (ECM) symbiosis is critical for the success of seedlings once planted in the field. To improve our knowledge of ECM fungi that inhabit bare-root nursery stock of Scots pine and understand factors that influence their diversity, we studied the assemblages of ECM fungi present across 23 bare-root forest nurseries in Poland. Nursery stock samples were characterized by a high level of ECM colonization (nearly 100%), and a total of 29 ECM fungal taxa were found on 1- and 2-year-old seedlings. The diversity of the ECM community depended substantially on the nursery and age of the seedlings, and species richness varied from 3–10 taxa on 1-year-old seedlings and 6–13 taxa on 2-year-old seedlings. The ECM fungal communities that developed on the studied nursery stock were characterized by the prevalence of Ascomycota over Basidiomycota members on 1-year-old seedlings. All ecological indices (diversity, dominance, and evenness) were significantly affected by age of the seedlings, most likely because dominant ECM morphotypes on 1-year-old seedlings (Wilcoxina mikolae) were replaced by other dominant ones (e.g., Suillus luteus, Rhizopogon roseolus, Thelephora terrestris, Hebeloma crustuliniforme), mostly from Basidiomycota, on 2-year-old seedlings. Across all nurseries, negative correlations were identified for diversity metrics and soil N or C, indicating that mineral and organic fertilization contributes to the differences in the ECM fungal communities in nurseries. We discuss the ecological and practical implications of the composition and diversity of ECM fungi occurring on bare-root planting stock of Scots pine.

DNA-Metabarcoding of Belowground Fungal Communities in Bare-Root Forest Nurseries: Focus on Different Tree Species.

The production of tree seedlings in forest nurseries and their use in the replanting of clear-cut forest sites is a common practice in the temperate and boreal forests of Europe. Although conifers dominate on replanted sites, in recent years, deciduous tree species have received more attention due to their often-higher resilience to abiotic and biotic stress factors. The aim of the present study was to assess the belowground fungal communities of bare-root cultivated seedlings of Alnus glutinosa, Betula pendula, Pinus sylvestris, Picea abies and Quercus robur in order to gain a better understanding of the associated fungi and oomycetes, and their potential effects on the seedling performance in forest nurseries and after outplanting. The study sites were at the seven largest bare-root forest nurseries in Lithuania. The sampling included the roots and adjacent soil of 2–3 year old healthy-looking seedlings. Following the isolation of the DNA from the individual root and soil samples, these were amplified using ITS rRNA as a marker, and subjected to high-throughput PacBio sequencing. The results showed the presence of 161,302 high-quality sequences, representing 2003 fungal and oomycete taxa. The most common fungi were Malassezia restricta (6.7% of all of the high-quality sequences), Wilcoxina mikolae (5.0%), Pustularia sp. 3993_4 (4.6%), and Fusarium oxysporum (3.5%). The most common oomycetes were Pythium ultimum var. ultimum (0.6%), Pythium heterothallicum (0.3%), Pythium spiculum (0.3%), and Pythium sylvaticum (0.2%). The coniferous tree species (P. abies and P. sylvestris) generally showed a higher richness of fungal taxa and a rather distinct fungal community composition compared to the deciduous tree species (A. glutinosa, B. pendula, and Q. robur). The results demonstrated that the seedling roots and the rhizosphere soil in forest nurseries support a high richness of fungal taxa. The seedling roots were primarily inhabited by saprotrophic and mycorrhizal fungi, while fungal pathogens and oomycetes were less abundant, showing that the cultivation practices used in forest nurseries secured both the production of high-quality planting stock and disease control.

Phytopathogenic fungi in forest nurseries of Middle Siberia

Abstract: The paper presents the results of phytopathogenic fungi determination in bare-root forest nurseries of Middle Siberia. Genetic analysis of pathogenic microflora of Pinus sylvestris L., Pinus sibirica Du Tour and Picea obovata Ledeb. seedlings allowed identification of 17 genera of micromycetes: Phoma Sacc., Lophodermium Chevall., Sclerophoma Hohn. (teleomorph Sydowia Bres.), Cladosporium Link, Alternaria Nees, Typhula (Pers.) Fr. etc. Most frequently detected fungi represented genera Phoma (23.7 %) and Lophodermium (23.6 %). Pinus sylvestris L. seedlings harboured the highest diversity of fungal taxa. Seven genera of microscopic fungi (Phoma sp., Didymella sp., Alternaria sp., Cladosporium sp., Lophodermium sp., Gremmenia sp., Sclerophoma sp.) were detected in all studied forest zones: taiga, forest-steppe and Southern-Siberian mountain. The obtained results demonstrate the usefulness of DNA analysis for the identification of phytopathogenic fungi in forest nurseries of Middle Siberia with several implications for increasing the efficacy of forest management.

Ectomycorrhizal community structure of the admixture tree species Betula pendula, Carpinus betulus, and Tilia cordata grown in bare-root forest nurseries

In many European countries, recent policies and forest management have been striving to restore and increase forest biodiversity. One of the ways to achieve this goal is by increased planting of admixture tree species, such as birch, hornbeam or lime, after clearcutting or in older, otherwise homogenous forest stands. However, because admixture forest tree species present less economical value than trees such as pine or oak, they are object of fewer studies, and in this context their mycorrhizal relations are not fully known. Describing them would further aid the use of such trees in forest management. This study focused on the ectomycorrhizal (ECM) fungal communities of two-years-old silver birch (B. pendula L.), European hornbeam (C. betulus L.) and small-leaved lime (T. cordata Mill.) seedlings under bare-root forest nursery conditions. The ECM fungal partners of the studied trees were identified based on the molecular approach, and the uncovered community structure was analyzed in context of the local soil chemical parameters.We found that the ECM fungal communities of admixture tree species in bare-root nurseries are of high diversity, and contain a wide array of fungal species. Our study identified the highest taxa richness (23 taxa) associated with the roots of hornbeams and limes, followed closely (21 taxa) by birch. Surprisingly, ECM fungal communities of lime (family Malvaceae) were more similar to hornbeam and birch (family Betulaceae) than the two were to each other. The lime ECM fungal communities were also the least divergent across the five tested nurseries, showing little response to differences in the soil chemistry. The most abundant and frequent fungi found in the study were Tuber (average relative abundance: 18.9%) and Hebeloma (average relative abundance: 18.4%) species. Some of the fungal taxa we recorded have never before been identified under nursery conditions (e.g., Lactarius pubescens, Leccinum holopus, Pachyphloeus melanoxantha, Russula grata). Pachyphloeus melanoxantha is a rare species in Europe, and this study recorded one of its first records in Poland. Our results present not only a description of ECM associations of tested trees (providing the first ever description of young hornbeam ECM communities), but also may have practical implications both for producing planting stock of these admixture trees, and for the later replanting of those into forest stands.

The Impact of Effective Microorganisms (EM) and Organic and Mineral Fertilizers on the Growth and Mycorrhizal Colonization of Fagus sylvatica and Quercus robur Seedlings in a Bare-Root Nursery Experiment

Every year there are changes in the register of fungicides available for forestry. It is proactive to develop a new strategy to minimise the application of chemical methods and replace them with natural and biological fungal control options. This study compares the influence after one growing season in a bare-root forest nursery of (a) effective microorganisms (EM) consisting of mixed cultures of beneficial and naturally-occurring microorganisms, (b) the organic fertilizer Actifos (Act), and (c) the mineral fertilizer Busz Forte (BF) on the growth and mycorrhizal colonization of two common forest deciduous tree species: Fagus sylvatica and Quercus robur. None of the analysed growth parameters (root collar diameter, length of shoots and roots, dry mass of shoots, and roots) of either tested tree species differed significantly among treatments. For both tree species, seedlings treated with EM exhibited partnerships with a smaller species richness of mycorrhizae than did seedlings in other treatments. Moreover, EM treatment significantly increased the abundance of non-vital root tips for both species. By contrast, BF exerted a negative effect on F. sylvatica non-vital mycorrhiza abundance. Based on morphological and molecular identification, a total of 11 ectomycorrhizal (ECM) fungal taxa were detected in this study; three species (Peziza ostracoderma, Scleroderma areolatum and Cenococcum-like) were shared between both plant species. Across treatments, the most abundant ECM fungal species on F. sylvatica roots were Pezizaceae sp. (51.1%) and Hebeloma sp. (38.1%), while Peziza ostracoderma (26.8%), Naucoria salicis (24.1%), and Scleroderma areolatum (16.9%) were the most abundant taxa on Q. robur seedling roots. Our data indicate a negative effect of EM on ectomycorrhizal colonisation and on species richness of ECM fungi associated with F. sylvatica and Q. robur seedlings. None of the tested products had a negative effect on seedling growth, but seedlings treated with EM were characterised by a significant higher abundance of non-vital mycorrhizae.

Forest litter amendment during nursery stage influence field performance and ectomycorrhizal community of Scots pine (Pinus sylvestris L.) seedlings outplanted on four different sites

Our recent studies have demonstrated that forest litter used in a bare-root forest nursery promoted survival and growth of two-year-old Scots pine seedlings and positively shaped the development of their ectomycorrhizal (ECM) fungal communities. To determine whether the beneficial effects of litter treatment can be extended to the next growing seasons, litter-treated seedlings were outplanted to four sites with different environmental conditions: forest clear-cut (S1), area formerly polluted by emissions from nitrogen fertilizer plant (S2), abandoned agricultural land (S3) and coastal sand dunes (S4). Seedlings grown in mineral nursery soil without litter amendment served as controls. Height and survival of seedlings were measured over three consecutive years after outplanting. At the end of the third growing season, the mycorrhizal status of seedlings was assessed using DNA-based identification techniques.Litter treatment during the nursery phase significantly improved the height of seedlings at the end of the first growing season at all tested sites. In the second and third growing seasons after outplanting, the heights of litter treated seedlings remained greater compared to control seedlings at three of the four sites; however, at the abandoned agricultural site (S3), significantly lower growth of litter-treated seedlings was observed. After the third growing season, the differences in seedling heights at the forest clear-cut (S1) and the site formerly polluted by nitrogen (S2) were not statistically significant. Survival of all outplanted seedlings varied by season and study site, but litter treated seedlings showed a clear tendency towards enhanced survival. Three years after outplanting, the survival rates of litter-treated seedlings ranged from approximately 81% at S4 to 96% at S2; for control seedlings, survival rates ranged from 63% at S4 to 81% at S3. At sites S1, S2 and S4, the survival of litter-treated seedling was significantly higher.There was a substantial transformation in ECM community composition with low persistence of suilloid mycorrhizas for both litter-treated and control seedlings three years after outplanting. Two-way analysis of similarities (ANOSIM) indicated that differences in ECM fungal community composition across seedlings from different sites likely were due to site specificity rather than previous litter treatment.Our results indicated that nursery soil amended with pine forest litter creates favourable conditions for the production of pine seedlings with better root quality and high abundance of suilloid mycorrhizas, thus allowing for potential reductions in mortality after outplanting on unfavourable sites.

First Report of Fusarium proliferatum Causing Fusarium Root Disease on Sugar Pine (Pinus lambertiana) in a Forest Container Nursery in California

Fusarium species, specifically F. commune, F. proliferatum, and F. solani, can cause severe damping-off and root disease in container and bareroot forest nurseries throughout North America. Many conifer and hardwood species can be affected, but Douglas-fir (Pseudotsuga menziesii), western white pine (Pinus monticola), and ponderosa pine (P. ponderosa) are known to be susceptible to Fusarium root disease (Stewart et al. 2012).

Forest litter as the mulch improving growth and ectomycorrhizal diversity of bare-root Scots pine (Pinus sylvestris) seedlings

In this paper, we report the influence of pine, oak and spruce forest litter on the growth and ectomycorrhizal (ECM) formation of Scots pine seedlings after the first growing season in a bare-root forest nursery. The mixture of collected forest litters and humus were used to obtain a 20-cm mulching layer on the prepared seedbeds. The concentrations of all nutrients and the C/N ratio of growth media were significantly higher in forest litter treatments than in negative control represented by mineral soil without litter. Addition of each forest litter type significantly enhanced pine seedling height and root-collar diameter compared to negative control. A significant positive influence on dry mass of stem, needles, roots and total dry mass of the seedling has been found only for pine litter. Based on molecular identification, seven ECM fungal taxa (Wilcoxina mikolae, Suillus luteus, Cenococcum geophilum, Meliniomyces bicolor, Laccaria laccata, unidentified Atheliaceae, unidentified Ascomycetes) were distinguished in the observed mycorrhizal communities. Each forest litter type significantly increased the total number of mycorrhizal tips and ECM fungal diversity compared to the control soil. However, results showed a lack of significant differences in species composition and relative abundance of ECM fungi between different litter types. Such result suggests that forest litter has not been a key source of inoculum for tested fungal species, as root systems of all pine seedlings from different litter types were dominated by a few nursery- adapted ECM fungi, probably originating from natural air-borne inoculum. Our data rather indicate that forest litter considerably improves environmental conditions for development of ECM fungi previously present in the nursery soil. Therefore, any of the forest litter types used in our studies may be able to promote planting stock quality on a small scale in the nursery phase.

Diversity of ectomycorrhizal fungus assemblages on nursery grown European beech seedlings

Abstract• ContextAn important feature of forest nursery management is the production of first-rate planting stock, which is closely connected with an adequate development of ectomycorrhizas on seedling roots.• AimsThe aim of this study was to provide a detailed assessment of the ectomycorrhizal (ECM) fungal diversity of European beech grown in bare-root forest nursery conditions.• MethodsMorphological and molecular analyzes were used to identify ECM fungi, quantify fungal richness, and record differences in the relative abundance of individual taxa.• ResultsTwenty-seven different mycorrhizal fungal taxa were found in four tested nurseries. Of these 27, only 6 were present in more than one nursery. Taxa richness in individual nurseries ranged from 6 to 13, indicating that ECM colonization potential is nursery-dependent. The most frequent taxa were:Tubersp. 1,Cadophorasp.,Cenococcum geophilumagg.,Hebeloma sacchariolens, andLaccaria tortilis.According to the analysis of similarity, ECM fungal communities were significantly different between nurseries (R = 0.7741;p < 0.0001).• ConclusionBeech seedlings grown in bare-root nurseries are colonized by a highly diverse suite of ECM fungi; thus, artificial inoculation of seedlings is generally not necessary in nursery practice.

Ectomycorrhizal fungal communities of pedunculate and sessile oak seedlings from bare-root forest nurseries

In this study, we present the detailed molecular investigation of the ectomycorrhizal (ECM) community of Quercus petraea and Quercus robur seedlings grown in bare-root forest nurseries. In all tested oak samples, mycorrhizal colonization was nearly 100%. Morphological observation and molecular investigations (sequencing of fungal ITS rDNA) revealed a total of 23 mycorrhizal taxa. The most frequent and abundant fungal taxa were Hebeloma sacchariolens, Tuber sp., and Peziza sp.; from the detected fungal taxa, 20 were noted for Q. petraea and 23 for Q. robur. Depending on the nursery, the species richness of identified ECM fungal taxa for both oak species ranged from six to 11 taxa. The mean species richness for all nurseries was 5.36 and 5.82 taxa per Q. petraea and Q. robur sample, respectively. According to the analysis of similarity, ECM fungal communities were similar for Q. petraea and Q. robur (R = 0.019; p = 0.151). On the other hand, detected fungal communities were significantly different between nurseries (R = 0.927; p < 0.0001). Using the Spearman rank correlation, it was determined that the ectomycorrhizal diversity (in terms of richness, the Shannon diversity, evenness, and Simpson dominance indices) is significantly related to the soil parameters of each nursery. We conclude that individual nursery may be considered as separate ecological niches that strongly discriminate diversity of ECM fungi.

Ectomycorrhizal status of Norway spruce seedlings from bare-root forest nurseries

We examined the ectomycorrhizal communities associated with Norway spruce seedlings grown in 16 bare-root nurseries in northwest Poland. One through four-year-old seedlings were examined and compared. We found 11 morphotypes in total with an average of 2.7 morphotypes per nursery. Among these 11 morphotypes, RFLP-analysis detected 17 distinct RFLP-patterns. By comparison with the available reference material, 12 of these could be identified to genus or species. These were Amphinema byssoides, Hebeloma crustuliniforme, Hebeloma longicaudum, Paxillus involutus, Thelephora terrestris, Cenococcum geophilum, Phialophora finlandia, Tuber sp., Wilcoxina mikolae, Wilcoxina sp. 1, Wilcoxina sp. 2 and Tricharina ochroleuca. The five unidentified morphotypes were: basidiomycetes ITE.5 and four ascomycetes designated as IDPAN.1, IDPAN.2, IDPAN.3 and IDPAN.4 that in morphotyping were classified as an E-strain. The ascomycete W. mikolae was predominant, whereas the basidiomycetes were less common. ECM community of Norway spruce seedlings from bare-root nurseries were not structured in association with soil pH and nutrient status of the host plant. The consistent presence of inocula of ascomycete symbionts in the substrate from all nurseries is quite notable and may reflect their adaptation and/or resistance to highly transformed nursery soil substrates compared to symbionts from the Basidiomycota.

Damping-Off of Beech Seedlings Caused by Fusarium avenaceum in Italy.

During May of 2004, damping-off of an estimated 70% of beech (Fagus sylvatica L.) seedlings was observed in a bare-root forest nursery located in northern Italy. Twenty-eight days after sowing, cotyledonary leaves were chlorotic, wilted, and occasionally desiccated; stem and collars appeared stunted and discolored with yellowish gray-to-brownish longitudinal streaks arising from the foot region, and rootlets were partially to completely rotten. No fruiting bodies were present on or near the damaged regions. Seedling establishment was poor within the disease foci that gradually increased in size. Longitudinal sections through the damaged stems showed dark brown streaks in the vascular tissue, and microscopic examination revealed that vessels frequently contained mycelium. Ten symptomatic plants were selected, and isolations were made from the necrotic margins of stems previously surface sterilized with 1% sodium hypochlorite and thoroughly rinsed, longitudinally cut into two parts 5-mm long, placed on potato dextrose agar (PDA), and incubated at 22 ± 1°C for 5 days in the dark. Although a variety of microorganisms were isolated, Fusarium avenaceum (Fr.:Fr.) Sacc. (1) was always recovered. Artificial inoculations with the fungus were made on 20-day-old, container-grown beech seedlings. The epidermis surrounding the collar was surface sterilized with 1% sodium hypochlorite, rinsed, and gently scraped with a sterile scalpel. After masking the rest of the plant with a plastic sheet, the wound was sprayed with a conidial suspension containing 103 macroconidia per cm3 in water and sealed with Parafilm. Controls were treated the same way but with sterile water. Each treatment was applied to 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day). After 20 days, wounds treated with F. avenaceum showed necrotic lesions that developed into small patches of dead epidermis. Radial sections through the stem 2 cm above the inoculation site from five plants showed the presence of mycelium in the vessels, from which the fungus was reisolated. Thirty days postinoculation, the remaining five plants showed the same symptoms observed in the nursery, and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium were observed in the inner tissues of control plants. The pathogenicity test was repeated twice with the same results. The fungus was not detected by culturing 100 surface-sterilized seeds from the same stock that had been sown in the nursery. F. avenaceum has a broad host range including angiosperms and gymnosperms, and the described symptoms are fairly typical (2). To our knowledge, this is the first report of this disease in Italy. Further research on fungal survivability in nursery soil and plant debris is in progress. The isolate is preserved in the Centraalbureau voor Schimmelcultures (NL) collection as no. 115957.

Atmospheric emissions of methyl isothiocyanate and chloropicrin following soil fumigation and surface containment treatment in bare-root forest nurseries

Methylisothiocyanate (MITC) and chloropicrin (CP) are alternatives to methyl bromide for soil fumigation. However, surface transport of MITC emission has been cited as the cause for seedling damage in adjacent fields at several bare-root forest-tree nurseries. Field experiments were conducted at nurseries in Wisconsin and Georgia to measure air emissions of MITC and CP after fumigation. Four treatments were tested as combinations of two fumigants (dazomet or coapplication of CP and metam sodium) and two surface containment treatments (tarp or water seal). A very small percentage (&lt;5%) of the applied equivalent of MITC was lost through either surface treatment over a 2-week period, and lower emissions occurred with the water seal. Cumulative emissions of CP accounted for 10%–22% of the applied CP. With all surface containment treatments, more than 70% of total cumulative emissions of either MITC or CP occurred within 1 week of application. Either surface containment treatment can be used by nursery managers to reduce risk of MITC emissions that could cause damage to nearby seedling crops or harm to humans.

Dose effect in the dual inoculation of an ectomycorrhizal fungus and a mycorrhiza helper bacterium in two forest nurseries

We inoculated disinfected soil at two Douglas-fir bareroot forest nurseries with three doses (8×10 5, 8×10 7 and 8×10 9 cfu m −2) of the rifampin-resistant mycorrhiza helper bacterium Pseudomonas fluorescens strain BBc6R8 and the ectomycorrhizal fungus Laccaria bicolor strain S238N. In one of the two nurseries, two doses of fungal inoculum (50 and 100 mg m −2 dry weight (DW) mycelium entrapped in alginate beads at the constant dose of 1 l m −2) were tested. For all bacterial treatments the density of P. fluorescens BBc6R8 in the soil, determined by dilution plating, dropped below the detection limit (10 −2 cfu g −1 DW soil) 2 weeks after inoculation. Fifteen weeks after inoculation, the introduced bacterium could be detected by enrichment only in the treatments inoculated with the highest bacterial dose. Two years after inoculation, P. fluorescens BBc6R8 could not be detected in the soil of any of the bacterial treatments. Five months after inoculation and sowing, bacterial inoculation significantly increased the percentage of mycorrhizal short roots on plants inoculated with either low or high amounts of L. bicolor, in one of the two nurseries. The lowest bacterial dose increased mycorrhizal colonization from 45 to 70% in plants inoculated with the low amount of fungal inoculum, and from 64 to 77% in plants inoculated with the high amount of fungal inoculum. The lowest bacterial dose increased mycorrhizal colonization more than the highest bacterial dose. The same L. bicolor mycorrhizal index (70%) was obtained with 50 mg m −2 DW mycelium plus the bacterium than with twice this fungal dose and no bacterium (64%). Two years after inoculation, the height of the mycorrhizal Douglas-firs in the other nursery was significantly increased by the lowest bacterial dose (from 40.7 to 42.6 cm). These results indicate that co-inoculating a helper bacterium together with an ectomycorrhizal fungus can be an efficient way of optimizing controlled mycorrhization techniques for the production of high-quality Douglas-fir planting stocks. They also confirm that BBc6R8 acts at a low population density (less than 10 2 cfu g −1 soil); this contrasts with most PGPR effects discussed in the literature, where the minimal inoculation dose of 10 5 cfu g −1 soil is required to obtain the beneficial effect.

Characterization of Rhizoctonia species involved in tree seedling damping-off in French forest nurseries

A total of 166 Rhizoctonia isolates were obtained from damped-off pine seedlings grown on soils originating from two bareroot forest nurseries in France. A majority of these isolates, 70%, had multinucleate cells and were identified as Rhizoctonia solani. R. solani isolates could be assigned to three anastomosis groups: AG 2-1, AG 4 the most prevalent one and AG 5. They were all pathogenic to pine seedlings. Isolates belonging to AG 5 were most aggressive, resulting in post-emergence damping-off in 99% of the test seedlings, Pinus nigra subsp. Laricio. The damping-off severity for AG 4 and AG 2-1 were 68 and 25% respectively. Possible thermic affinities of AG 2-1 and AG 4 isolates were discussed.

Effect of density control and undercutting on root morphology of 1+0 bareroot hardwood seedlings: five-year field performance of root-graded stock in the central USA

The Hardwood Quality Nursery Cooperative (bareroot forest nurseries in 5 midwestern states) initiated a series of studies in 1987 to evaluate red oak (Quercus rubra L.), and black walnut (Juglans nigra L.) seedling performance as a function of cultural treatments and seedling root system morphology. Seedlings were grown at three densities (32, 64, and 128 stems m-2for red oak; 32, 64, and 96 stems m-2for black walnut), and half of the density plots were undercut. Seedlings received fertilizer, weeding, and irrigation treatments customary to their respective nurseries. Seedlings were lifted, measured, and outplanted in their respective states as completely random individual tree plots during spring 1988. Survival, height, and diameter were evaluated annually through 1992. Seedling height, diameter, and number of permanent first-order lateral roots (FOLR) decreased with increasing bed density. At a given density, undercutting produced smaller seedlings (for both height and diameter) that had greater numbers of FOLR. Numbers of FOLR influenced seedling performance after outplanting. Red oak seedlings with at least 5 FOLR and black walnut with at least 7 FOLR had better survival and growth than seedlings with fewer roots.

Effect of dual inoculation of Douglas fir with the ectomycorrhizal fungus Laccaria laccata and mycorrhization helper bacteria (MHB) in two bare-root forest nurseries

Douglas fir (Pseudotsuga menziesii) seedlings in two bare-root forest nurseries were inoculated with the ectomycorrhizal fungus Laccaria laccata, together or not with one of five mycorrhization helper bacteria isolated from L. laccata sporocarps or mycorrhizas and previously selected by in vitro and glasshouse screenings. With the most efficient MHB isolates, when compared to the control with no bacteria, the percent of mycorrhizal short roots was increased from 60 to 90 or from 80 to 100, depending on the nursery, with inoculation doses as low as 106 living cells per m2. A dual inoculum made of calcium alginate beads containing the two microorganisms appears to be a valuable technique for increasing the efficiency of ectomycorrhizal inoculation of planting stocks in forest nurseries.