Radial growth and climate responses of white oak (Quercus alba) and northern red oak (Quercus rubra) at the northern distribution limit of white oak in Quebec, Canada

Aim The objectives of this study were: (1) to compare radial growth patterns between white oak (Quercus alba L.) and northern red oak (Quercus rubra L.) growing at the northern distribution limit of white oak; and (2) to assess if the radial growth of white oak at its northern distribution limit is controlled by cold temperature. Location The study was conducted in three regions of the Ottawa valley in southern Québec. All stands selected were located at the northern limit of distribution of Q. alba. Methods Twelve mixed red and white oak stands were sampled and increment cores were extracted for radial growth analyses. For each oak species, 12 chronologies were derived from tree‐ring measurement (residual chronologies). Principal components analysis and redundancy analysis were used to highlight the difference between radial growth in both species and to determine their radial growth–climate association. Results There was little difference between the radial growth of each species; Q. alba, however, exhibits more year‐to‐year variation in growth than Q. rubra. More than 65% of the variance in radial growth was shared among sites and species. Both species showed a similar response to climate, which suggested that the limit of distribution of Q. alba might not be determined by effects on growth. Both species had a classic response to climate and drought in the early growing season. Main conclusions The northern distribution limit of Q. alba does not appear to be directly controlled by effects on growth processes as indicated by the similarities in radial growth and response to climate between the two species. The location of the stands on southern aspects suggested that cold temperature could have been a major factor controlling the distribution limit of Q. alba. However, it is speculated that stands growing on southern aspects may be more prone to forest fires or to drought, which would favour the maintenance and establishment of oaks, and of Q. alba in particular. Models relating the northern distribution limits of species to broad climate parameters like annual mean temperature will need to be reviewed to incorporate more biologically relevant information. Such assessments will in turn provide better estimates of the effect of climate changes on species distribution.     

Carbon dioxide assimilation of hardwood seedlings in relation to community dynamics in central illinois

Summary Field measurements of net assimilation and respiration for seedlings of four hardwood species were made periodically over a growing season with soil moisture tension maintained between 0 and 0.75 bar. Total net assimilation per day was significantly greater for Acer saccharum than either Quercus rubra or Quercus alba and for Quercus macrocarpa as compared with Q. rubra, when measurements were made under natural shade conditions and light intensity varied from 80 to 120 ft-c. Mean light compensation points determined under canopy shade were 50.3, 53.5, 87.2, and 102.5 ft-c., respectively, for Acer saccharum, Quercus macrocarpa, Q. rubra, and Q. alba. In a 0.04-hectare canopy opening, total net assimilation per day was not significantly different between Q. rubra, Q. alba, and A. saccharum but was significantly greater for Q. macrocarpa than Q. alba and A. saccharum. Relationships between photosynthetic efficiency and successional characteristics of these species are inferred from the data.     

Tannin assays in ecological studies: Lack of correlation between phenolics,proanthocyanidins and protein-precipitating constituents in mature foliage of six oak species

Summary There is no correlation between protein-precipitating capacity and either total phenolic or proanthocyanidin content of extracts of mature foliage from six species of oaks: Quercus alba (white oak), Q. bicolor (swamp white oak), Q. macrocarpa (bur oak), Q. palustris (pin oak), Q. rubra (red oak), and Q. velutina (black oak). It is argued that studies which probe the role of tannins in the selection and utilization of food by herbivores should include a protein-precipitation assay, since such an assay provides a measure of the property of tannins which is presumed to contribute to their utility as defensive compounds. A convenient modification of the bovine serum albumin (BSA) precipitation assay, which measures the amount of protein precipitated when a plant extract is added to a BSA solution, is described. Advantages of this procedure recommend its routine adoption in studies of the role of tannins in plant-herbivore interactions.     

Colonization, survival, and causes of mortality of Camerariu hamadryadella (Lepidoptera: Gracillariidae) on four species of host plants

Abstract.

• 1 The abundance, survival, and causes of mortality of Cameraria hamadryadella (Clemens) (Lepidoptera: Gracillariidae) were examined on four host plant species in Virginia, U.S.A. Quercus alba L. and Q.rubra L. are native within the geographic range of C.hamadryadella, and Q.robur L. and Q.benderi Baenitz are exotic. Q.robur is native to Europe, North Africa, and Asia and was probably introduced prior to 1850, and Q.benderi is of hybrid origin and introduced to cultivation before 1900. Q.alba and Q.robur are in the subgenus Lepidobalanus (white oaks), and Q.rubra and Q.benderi are in the subgenus Erythrobalanus (red oaks).
• 2 Larval mines of C. hamadryadella were abundant on both white oak species, including the exotic Q.robur, but were rare on host plants in the red oak subgenus. Un-hatched eggs of C.hamadryadella were not observed on red oaks. Other observations on host distribution indicate that C.hamadryadella is rarely found on red oaks. These observations are interpreted as circumstantial evidence that C. hamadryadella generally avoids ovipositing on red oaks.
• 3 Survival of C.hamadryadella to the adult stage was similar among all host species, but larvae tended to survive longer on hosts in the red oak subgenus. The observation of higher survival rates of early instar larvae on red oaks suggests that no nutritional or secondary chemical barrier reinforces the observed pattern of oviposition.
• 4 Significant differences in the distribution of the causes of mortality were detected between native and exotic host plant species. Larvae and pupae on native hosts were more likely to die because of predation, while those on exotic host plants were more likely to die because of parasitism and host feeding by adult female parasitoids. This pattern could arise because parasitoids prefer to forage on exotic host plants or because predators avoid foraging on exotic plants.
• 5 This study shows for C. hamadryadella that the only barriers to colonization and use of exotic hosts, in the white and red oak subgenera, are the presence of cues sufficient to stimulate oviposition and/or the absence of cues to deter oviposition. It also suggests that the presence of closely related native host plants in the region of introduction will increase the probability that exotic plants will be colonized by phytophagous insects.

     

Importance of fragmentation-tolerant species as seed dispersers in disturbed landscapes

Forest fragmentation can negatively affect plants if animal seed-dispersers become locally extinct in fragments. We conducted a 2-year experiment to evaluate the importance of tree squirrels (Sciurus) as seed dispersers for Quercus, Carya, and Juglans, and to assess dispersal consequences in patches where fragmentation-sensitive eastern gray squirrels (Sciurus carolinensis) are absent. We accounted for fates of ∼15,700 seeds from five tree species in four exclosure treatments at 18 fragments during a high (2003–2004) and low seed (2004–2005) year. Two treatments excluded Sciurus to mimic disperser loss. We sampled nut-tree seedling density at 259 sites across eight watersheds, half of which were too fragmented to support S. carolinensis, but supported fragmentation-tolerant fox squirrels (Sciurus niger). Autumn-to-spring seed survival was low (∼1%) for all species during low seed production. During high seed production, survival was higher for Juglans nigra (20%) and Carya ovata (16%) than for three Quercus species (∼4% for Quercus palustris and Quercus rubra in two exclosure types; ∼1% for Quercus alba in all treatments). Survival of J. nigra, C. ovata, and Q. rubra was ≥2.1–7.7 times higher for seeds in exclosures that Sciurus could access. Seed displacement distance was higher in the low seed than the seed-rich year, but the proportion of seeds surviving to greater distances was higher in seed-rich years for all seed types except Q. rubra. This affirms the importance of masting to seed survival and dispersal, but also suggests an advantage to trees of producing seed in non-mast years. Seedling densities were comparable in watersheds with and without S. carolinensis. These results demonstrate the importance of tree squirrels as dispersers of nut-bearing trees, but suggest that fragmentation may not disrupt dispersal of certain species if losing S. carolinensis from disturbed landscapes is compensated for by fragmentation-tolerant fox squirrels (S. niger).     

In vitro regeneration of the important North American oak species <Emphasis Type="Italic">Quercus alba</Emphasis>, <Emphasis Type="Italic">Quercus bicolor</Emphasis> and <Emphasis Type="Italic">Quercus rubra</Emphasis>

North American oak species, with their characteristic strong episodic seasonal shoot growth, are highly problematic for clonal micropropagation, resulting in the inability to achieve a stabilized shoot multiplication stage. The potential for initiating and proliferating shoot cultures derived from Quercus alba, Q. bicolor and Q. rubra explants was investigated, and a micropropagation method for these species was developed. Branch segments from 6 to 7-year-old trees were forced-flushed and the forced shoots were used as source of explants for culture initiation. A consistent shoot multiplication stage was achieved, in 13 of the 15 genotypes established in vitro, although marked differences occurred in explants from different genotypes/species. The control of efficient shoot multiplication involved the culture of decapitated shoots in a stressful horizontal position on cytokinin-containing medium with a sequence of transfers within a 6-week subculture cycle, which was beneficial to overcoming the episodic character of shoot growth. During each subculture cycle, the horizontally placed explants were cultured on media containing 0.2 mg l⁻¹ benzyladenine (BA) for 2 weeks with two successive transfers (2 weeks each) to fresh medium with 0.1 mg l⁻¹ BA, giving a 6-week subculture cycle. The general appearance and vigor of Q. alba and Q. bicolor shoot cultures were improved by the inclusion of both 0.1 mg l⁻¹ BA and 0.5 mg l⁻¹ zeatin in the medium used for the second transfer within the 6-week subculture cycle. Addition of AgNO₃ (3 mg l⁻¹) to the shoot proliferation medium of Q. rubra had a significant positive effect on shoot development pattern by reducing deleterious symptoms, including shoot tip necrosis and early senescence of leaves. The three species showed acceptable in vitro rooting rates by culturing microcuttings in medium containing 25 mg l⁻¹ indolebutyric acid for 48 h with subsequent transfer to auxin-free medium supplemented with 0.4% activated charcoal. Although an initial 5-day dark period generally improved the rooting response, it was detrimental to the quality of regenerated plantlets. However, activated charcoal stimulated not only the rooting frequencies, but it also enhanced plant quality, as evidenced by root, shoot and leaf growth.     

Unusual Slow Gating of Gap Junction Channels in Oocytes Expressing Connexin32 or Its COOH-Terminus Truncated Mutant

Gap junction channels are gated by a chemical gate and two transjunctional voltage (V _j)-sensitive gates: fast and slow. Slow V _j gate and chemical gate are believed to be the same. The slow gate closes at the negative side of V _j and is mostly inactive without uncouplers or connexin (Cx) mutations. In contrast, our present data indicate otherwise. Oocytes expressing Cx32 were subjected to series of −100 mV V _j pulses (12-s duration, 30-s intervals). Both peak (PK) and steady-state (SS) junctional conductances (G _j), measured at each pulse, decreased exponentially by 50−60% (tau = ∼1.2 min). G _jPK dropped more dramatically, such that G _jSS/G _jPK increased from 0.4 to 0.6, indicating a drop in V _j sensitivity. Less striking effects were obtained with –60 mV pulses. During recovery, G _j, measured by applying 20 mV pulses (2-s duration, 30-s intervals), slowly returned to initial values (tau = ∼7 min). With reversal of V _j polarity, G _jPK briefly increased and G _jSS/G _jPK decreased, suggesting that V _j-dependent hemichannel reopening is faster than hemichannel closing. Similar yet more dramatic results were obtained with COOH-terminus truncated Cx32 (Cx32-D225), a mutant believed to lack fast V _j gating. The data indicate that the slow gate of Cx32 is active in the absence of uncouplers or mutations and displays unusual V _j behavior. Based on previous evidence for direct calmodulin (CaM) involvement in chemical/slow gating, this may also be CaM-mediated.     

Sequence characteristics and phylogenetic implications of the nrDNA internal transcribed spacers (ITS) in the genus <Emphasis Type="Italic">Nymphaea</Emphasis> with focus on some Indian representatives

Nymphaea, an aquatic perennial herb with exceptionally beautiful flowers and floating leaves, is well represented globally. Out of ten species reported from India, the internal transcribed spacers (ITS) region of nrDNA was investigated in seven species of Nymphaea viz. N. alba var. rubra, N. caerulea, N. × marliacea, N. nouchali, N. pubescens, N. rubra and N. tetragona. Barring N. pubescens, whereby double peaks detected in the sequencing chromatograms may be due to random mutations occurring in some of the ITS paralogues, the additional signals detected for N. alba var. rubra and N. rubra are probably influenced by recent hybridization and introgression. Our study on sequence characteristics of ITS 1 and ITS 2 revealed high G + C content (ITS 1, 45.5–48.4%; ITS 2, 50.2–51.5%) and sequence divergence. Percentage of sequence divergence based on substitution and substitution plus indels is 44.15 and 57.19, respectively, for the ITS 1; 29.74 and 47.96% were recorded for the ITS 2. Although highly variable, conserved motifs within the ITS 1 and ITS 2 region of Nymphaea were identified and are found to be common throughout the order Nymphaeales. Sequence analysis of the ITS 1 and ITS 2 failed to detect any variation between two morphotypes of N. nouchali, namely N. nouchali JD 06 and N. nouchali JD 07, differing in flower color and found at the same geographical location. However, on comparison with another specimen of N. nouchali found at a different location, they showed considerable variation in nucleotide composition. Complemented by sequence data retrieved from GenBank, phylogenetic tree reconstruction of the genus Nymphaea based on neighbor-joining, maximum parsimony, maximum likelihood and Bayesian inference methods is presented and discussed.     

Radiative properties of hardwood leaves to ultraviolet irradiation

Spectral reflectance and transmittance of leaves to ultraviolet irradiation were determined under laboratory conditions for seven species of hardwood trees, namely red oak (Quercus rubra, L), black oak (Q. velutina, Lamarch), white oak (Q. alba, L.), sugar maple (Acer saccharum), Norway maple (A. plantanoides), hickory (Carya tomemtosa), sweetgum (Liquidambar styraciflua), and black oak litter. The experimental system consisted of a solar simulator, an integrating sphere, and a spectroradiometer. Experiments were repeated three to five times for both adaxial and abaxial surfaces of fresh leaves chosen at randomly. The spectral distributions and simple averages of the radiative properties in the wavelength ranges of ultraviolet-B (UV-B, 280–320 nm) and ultraviolet-A (UV-A, 320–400 nm) were determined. The spectral distributions of reflectance were similar between adaxial and abaxial surfaces, although the magnitude varied among tree species. Leaf reflectance was very low for the ultraviolet spectrum in general and varied among species and between adaxial and abaxial surfaces. It was generally higher over the UV-A waveband compared to UV-B, and higher on the abaxial than adaxial surface. The broadband reflectance in the UV-A range (over all species) was 5.0 and 3.9% for abaxial and adaxial surface, respectively, compared to 3.5 and 2.8% in UV-B. The transmittance through leaves was extremely small in the UV-B (<0.1%) and nearly zero in the UV-A spectral range. Consequently, the absorptance of ultraviolet radiation by leaves, as determined from the measured reflectance and transmittance, was quite high, being more than 90% for all the combinations of species and wavebands examined. The reported results are useful for studies requiring spectral radiative properties of the examined leaves with respect to ultraviolet irradiation.     

Feeny revisited: condensed tannins as anti-herbivore defences in leaf-chewing herbivore communities of Quercus

Abstract. 1. Community level oak–tannin–insect patterns have been largely unexplored since Paul Feeny's ground‐breaking research. Two hypotheses were tested for Quercus velutina and Q. alba in the Missouri Ozarks: abundance and richness of leaf‐chewing herbivores are negatively correlated with foliar condensed tannin concentrations and variation in condensed tannin concentrations explains variation in herbivore community structure. 2. In 2001, foliar condensed tannins in the understorey and canopy of these two oak species were quantified simultaneously with censuses of herbivores in May, during leaf expansion, and in June and August, when leaves were fully expanded. Thirty‐eight of the 134 species encountered had densities sufficient to be analysed individually (n = 10). Of those, Acronicta increta (Noctuidae) and Attelabus sp. (Curculionidae), both oak specialists, were negatively correlated with condensed tannins in the canopy of Q. alba. One additional specialist, Chionodes pereyra (Gelechiidae), was marginally negatively correlated with condensed tannins in the understorey of Q. velutina. Understorey species richness of May Q. velutina herbivores was negatively correlated with condensed tannins, as were total canopy insect density and species richness of August herbivores on Q. alba. 3. Principal component analysis (PCA) of insect abundances indicated that understorey and canopy Q. velutina and Q. alba had different communities of leaf‐chewing insects. Furthermore, condensed tannin levels contributed significantly to variation in PCA scores for Q. velutina, explaining 25% of the total variation. 4. Overall, these results indicate that specialists were more likely than generalists both to correlate negatively with condensed tannins and to occur in lower tannin habitats; abundance and richness of both early and late season fauna correlated negatively with tannins; and species were more likely to correlate negatively with condensed tannins when feeding on Q. alba than on Q. velutina and when feeding in the canopy than in the understorey. Future studies of tannin–insect interactions should manipulate leaf quality in combination with manipulations of other factors that likely influence community structure.     

A nuclear DNA barcode for eastern North American oaks and application to a study of hybridization in an Arboretum setting

DNA barcoding has proved difficult in a number of woody plant genera, including the ecologically important oak genus Quercus. In this study, we utilized restrictionsite‐associated DNA sequencing (RAD‐seq) to develop an economical single nucleotide polymorphism (SNP) DNA barcoding system that suffices to distinguish eight common, sympatric eastern North American white oak species. Two de novo clustering pipelines, PyRAD and Stacks, were used in combination with postclustering bioinformatic tools to generate a list of 291 potential SNPs, 80 of which were included in a barcoding toolkit that is easily implemented using MassARRAY mass spectrometry technology. As a proof‐of‐concept, we used the genotyping toolkit to infer potential hybridization between North American white oaks transplanted outside of their native range (Q. michauxii, Q. montana, Q muehlenbergii/Q. prinoides, and Q. stellata) into a horticultural collection surrounded by natural forests of locally native trees (Q. alba and Q. macrocarpa) in the living collection at The Morton Arboretum (Lisle, IL, USA). Phylogenetic and clustering analyses suggested low rates of hybridization between cultivated and native species, with the exception of one Q. michauxii mother tree, the acorns of which exhibited high admixture from either Q. alba or Q. stellata and Q. macrocarpa, and a hybrid between Q. stellata that appears to have backcrossed almost exclusively to Q. alba. Together, RAD‐seq and MassARRAY technologies allow for efficient development and implementation of a multispecies barcode for one of the more challenging forest tree genera.     

Rhizobial Populations in Soils from Natural Acacia senegal and Acacia nilotica Forests in Mauritania and the Senegal River Valley

Eighty-two strains of rhizobia were isolated from soils taken from several sites in Mauritania and Senegal. These soil samples were collected from natural stands of Acacia nilotica and Acacia senegal. The soils from Mauritania were less rich in native rhizobia than the soils from Senegal. The strains were characterized using polymerase chain reaction–restriction fragment length polymorphism and by sequencing the rDNA 16S–23S intergenic spacer region (IGS). They were sorted into seven IGS groups. These groups were not associated with the geographical origin of the strains or with the host-plant species at the site where the soils were collected. Most of the strains were in three of the IGS groups (I, IV, and V). One representative strain from each IGS group was sequenced and showed that the strains were from the genus Mesorhizobium. IGS groups I, IV, and VI were close to the species M. plurifarium (AF34563), IGS groups IIand III were close to the species Mesorhizobium sp. (AF510360), IGS group V was close to the species Mesorhizobium sp. (AF510366), and IGS group VII was close to Mesorhizobium sp. (AF510346).     

Light acclimation at the end of the growing season in two broadleaved oak species

The ability of plants to increase their net CO₂ assimilation rate in response to increased irradiance is due to morphological and physiological changes, which might be related to their shade tolerance and leaf ontogeny, but few studies have considered morphology and physiology. Two sympatric oak species (the shade-tolerant Q. petraea and the comparatively shade-intolerant Q. pyrenaica) were grown in hydroponic solution in low-light (LL) and high-light (HL) conditions. 5 months after leaf expansion under these conditions, half of the LL plants were transferred to high light (TLH). Transfer of Q. pyrenaica, from low- to high light led to photoinhibition and after 21 days in higher light there was little acclimation of the maximum rate of carboxylation (V_Cmax) or the maximum rate of electron transport (J_max). Q. pyrenaica TLH plants showed lower stomatal conductance at all times compared to plants growing in LL. Stomatal closure was the main limitation to photosynthesis after transfer in Q. pyrenaica. The increase in evaporative demand upon TLH did not affect hydraulic conductivity of Q. pyrenaica. In contrast, the more shade-tolerant Q. petraea showed a greater degree of acclimation of gas exchange in TLH than Q. pyrenaica and two weeks after transfer gas-exchange rates were as high as in LL plants. In Q. petraea, the most important changes occurred at the level of leaf biochemistry with significant increase in V_Cmax that decreased the J_max/V_Cmax ratio below values recorded in HL plants. However, this potential increase in photosynthesis was at least partially hamstrung by a decrease in internal conductance, which highlights the importance of internal conductance in acclimation to higher light in mature leaves. Neither oak species reached the photosynthetic rates of HL plants; however a trend towards leaf acclimation was observed in Q. petraea while the transfer was harmful to the leaves of Q. pyrenaica developed in the shade.     

Development and Characterization of Genomic and Gene-Based Microsatellite Markers in North American Red Oak Species

Oaks (Quercus: Fagaceae) are ecological and economic keystones of many forested ecosystems but effective genetic management strategies are hindered by high levels of phenotypic plasticity within species and frequent hybridization among them. These same features, however, make oak communities suited for the study of speciation, hybridization, and genetic adaptation. Efforts to develop new and to adapt existing genomic resources to less-studied members of this genus should not only improve oak conservation and management but also aid the study of fundamental evolutionary processes. Here, we present a suite of 27 highly polymorphic simple sequence repeat (SSR) markers tested in four North American red oak (Quercus section Lobatae) species: Q. rubra, Q. ellipsoidalis, Q. coccinea, and Q. velutina. Five markers are genomic SSRs (gSSRs) — four novel and one previously transferred from Q. petraea — and 22 are gene-based SSRs derived from Q. robur and Q. petraea expressed sequence tags (EST-SSRs). Overall, levels of polymorphism detected with these primer pairs were high, with gene diversity (H _e) averaging 0.66 across all loci in natural populations. In addition, we show that EST-SSR markers may have the potential to detect divergent selection at stress-resistance candidate genes among closely related oak species.     

Phylogenetic diversity of rhizobia associated with horsegram [Macrotyloma uniflorum (Lam.) Verdc.] grown in South India based on glnII, recA and 16S-23S intergenic sequence analyses

Horsegram [Macrotyloma uniflorum (Lam.) Verdc.) is an important grain legume and fodder crop in India. Information on root nodule endosymbionts of this legume in India is limited. In the present study, 69 isolates from naturally occurring root nodules of horsegram collected from two agro-eco-climatic regions of South India was analyzed by generation rate, acid/alkali reaction on YMA medium, restriction fragment length polymorphism analysis of 16S-23S rDNA intergenic spacer region (IGS), and sequence analyses of IGS and housekeeping genes glnII and recA. Based on the rDNA IGS RFLP by means of three restriction enzymes rhizobia were grouped in five clusters (I–V). By sequence analysis of 16S-23S rDNA IGS identified genotypes of horsegram rhizobia were distributed into five divergent lineages of Bradyrhizobium genus which comprised (I) the IGS type IV rhizobia and valid species B. yuanmingense, (II) the strains of IGS type I and Bradyrhizobium sp. ORS 3257 isolated from Vigna sp., (III) the strains of the IGS type II and Bradyrhizobium sp. CIRADAc12 from Acacia sp., (IV) the IGS type V strains and Bradyrhizobium sp. genospecies IV, and (V) comprising genetically distinct IGS type III strains which probably represent an uncharacterized new genomic species. Nearly, 87% of indigenous horsegram isolates (IGS types I, II, III, and V) could not be related to any other species within the genus Bradyrhizobium. Phylogeny based on housekeeping glnII and recA genes confirmed those results found by the analysis of the IGS sequence. All the isolated rhizobia nodulated Macrotyloma sp. and Vigna spp., and only some of them formed nodules on Arachis hypogeae. The isolates within each IGS type varied in their ability to fix nitrogen. Selection for high symbiotic effective strains could reward horsegram production in poor soils of South India where this legume is largely cultivated.     

Variability and characterization of mycotoxin-producing Fusarium spp isolates by PCR-RFLP analysis of the IGS-rDNA region

In the present report, a total of 75 Fusarium spp isolates (35 of the Gibberella fujikuroi species complex, 26 of F. oxysporum, 7 of F. graminearum, 5 of F. culmorum, 1 of F. cerealis, and 1 of F. poae) from different hosts were characterized morphologically, physiologically and genetically. Morphological characterization was performed according to macroscopic and microscopic aspects. Physiological characterization was based on their ability to produce fumonisin B₁ (FB₁), fumonisin B₂ (FB₂), zearalenone (ZEA) and type B trichothecenes (deoxynivalenol, nivalenol and 3-acetyldeoxynivalenol). FB₁, FB₂, and ZEA were determined by liquid chromatography and trichothecenes by gas chromatography. Molecular characterization of isolates was carried out using an optimized and simple method for isolation of DNA from filamentous fungi and polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) of the intergenic spacer region (IGS) of the rDNA. The results indicated that G. fujikuroi complex isolates can be␣divided into low and high fumonisin producers. The haplotypes obtained with HhaI, EcoRI, AluI, PstI and XhoI enzymes provided very characteristic groupings of G. fujikuroi isolates as a function of host type and fumonisin producing capacity. F. graminearum, F. culmorum and F. cerealis isolates were high ZEA␣and type B trichothecene producers, while F. oxysporum and the G. fujikuroi complex isolates did not show this ability. The haplotypes obtained with CfoI, AluI, HapII, XhoI, EcoRI and PstI enzymes permitted to discern these five Fusarium species and G. fujikuroi complex isolates but the restriction patterns of the IGS region did not show any relationship with the geographic origin of isolates.     

Assemblages of native bryophytes in secondary forests with introduced Quercus rubra

We have studied the diversity of bryophytes in planted Polish post‐agricultural forests dominated by the native Scots pine Pinus sylvestris and the alien (North American) red oak Quercus rubra. The planted sites would be suitable for a mesic coniferous forest (abbreviation: CFS) or mesic broadleaved forest (abbreviation: BFS). We analysed the structure and composition of the bryophyte assemblages in relation to forest site and substrate availability. Special attention was paid to the introduced Q. rubra as a host species for native bryophytes. A total of 54 bryophyte species (9 liverworts and 45 mosses) were found in the 90 plots ( = phytosociological relevés, 10 × 10 m in area; 45 at each forest site) studied. DCA analysis showed that the bryophyte assemblages of the P. sylvestris–Q. rubra secondary forest community differed significantly between CFS and BFS sites; the similarity of the composition of bryophyte species was 36.8%. The substrate preferences (epigeic, epixylic, epiphytic), as well as the growth form and life form of the recorded bryophytes, also differed between CFS and BFS, while the proportion of bryophytes that had a particular life strategy was very similar. The introduced Q. rubra was inhabited by 28 bryophyte species, including two liverworts. This tree hosted 64% of the CFS and 47% of BFS bryophyte flora and as a host for epiphytes the species successfully fulfilled the functional role of the native oaks (Q. robur and Q. petraea). Thus, the introduction of Q. rubra may contribute to the restoration of post‐agricultural forests and to the conservation of epiphytic bryophyte species. On the other hand, the negative impact of Q. rubra observed on the ground flora (including bryophytes) puts the benefits of Q. rubra for the conservation of native biodiversity in general in question.     

Genotypic Characterization of Phage-Typed Indigenous Soybean Bradyrhizobia and Their Host Range Symbiotic Effectiveness

Analysis of genetic diversity among indigenous rhizobia and its symbiotic effectiveness with soybean cultivar is important for development of knowledge about rhizobial ecology. In India, little is known about the genetic resources and diversity of rhizobia nodulating soybean. Indigenous bradyrhizobia isolated from root nodules of soybean plants, collected from traditional cultivating regions of two states (Madhya Pradesh and Uttar Pradesh) of India, were screened for bacteriophage sensitivity to identify successful broad host range symbiotic effectivity. Of 172 rhizobial isolates, 91 showed sensitivities to eight lytic phages and form ten groups on the basis of sensitivity patterns. The genetic diversity of 23 isolates belonging to different phage groups was assessed along with that of strains USDA123 and USDA94 by the restriction fragment length polymorphism (RFLP) analysis of 16S rDNA, intergenic spacer (IGS) (16S–23S rDNA), and DnaK regions. RFLP analysis of 16S rDNA formed 5 groups, whereas 19 and 9 groups were revealed by IGS and the DnaK genes, respectively. The IGS regions showed many amplified polymorphic bands. Nine isolates which revealed high RFLP polymorphism in the abovementioned regions (16S rRNA, IGS, DnaK) were used for 16S rRNA sequence analyses. The results indicate that taxonomically, all isolates were related to Rhizobium etli, Bradyrhizobium spp., and Bradyrhizobium yuanmingense. The doubling time of isolates varied from 9 h (MPSR155) to 16.2 h (MPSR068) in YM broth. Five isolates which did not show cross infectivity with isolated phage strains were studied for symbiotic efficiency. All isolates showed broad host range symbiotic effectiveness forming effective nodules on Vigna mungo, Vigna radiata, Vigna unguiculata, and Cajanus cajan. The present study provides information on genetic diversity and host range symbiosis of indigenous soybean rhizobia typed by different phages.     

In situ regeneration of Pinus strobus and P. resinosa in the Great Lakes forest communities of Canada

Abstract. Two extensive forest vegetation survey datasets are explored, using ordination and classification, for evidence of in situ regeneration by Pinus strobus (Eastern white pine) and P. resinosa (Red pine). Ordination of tree species contributions to total basal area in 320 upland northern hardwood- conifer stands produced distinct stand groups for P.banksiana, P. resinosa, P. strobus and mesic hardwoods in an ascending sequence along the first axis. Quercus rubra (red oak), Q. alba (white oak) and tolerant conifer groups formed segregates from the hardwood complex along the second axis. P. strobus mixes with all other forest types, but P. resinosa is restricted to its own group. Seedlings and trees of P. strobus are more abundant than saplings, which are restricted to the pine and oak forests. Therefore, seed production, dispersal and seedling establishment seem to be less of a barrier to in situ regeneration by P. strobus than subsequent survival and growth. Canonical correspondence analysis of 170 pine-dominated stands from the Canadian Shield of Ontario, in which tree species variables are segmented into height-class pseudo- species, yielded no linear relationship between environmental features or stand structure and seedling densities of P. strobus. However, total tree basal area appears to impose an upper limit to seedling density on the forest floor. Strong correlations emerged between pine seedling density and understorey vegetation. Stand classification of the understorey vegetation, using constrained indicator species analysis, yielded distinct high and low seedling groups. Low pine seedling density was associated with abundant broadleaved shrubs, herbs and seedlings as well as feathermosses and tolerant conifers. High seedling density could not be ascribed to the presence of seedbed taxa, such as Polytrichum, but is ascribed to the absence of competition and other forms of inhibition in the understorey vegetation and down through the canopy profile. In situ regeneration of P. strobus does, therefore, occur but conditions over the forest landscape are largely restrictive.