Anthropogenic nitrogen (N) emissions can have considerable effects on terrestrial ecosystems, with chronic N deposition leading to changes in plant species composition. The Athabasca Oil Sands Region (AOSR) represents a large point source of N emissions, which has prompted concern for surrounding habitats. The objective of this study was to determine the relative importance of N deposition as a driver of plant species community composition against bioclimatic and soil chemical variables. Further, we sought to identify community thresholds in plant species composition across a N deposition gradient. This assessment was performed for 46 Jack pine (Pinus banksiana Lamb.)-dominant forest sites surrounding the AOSR spanning Alberta and Saskatchewan. In total, 35 environmental variables were evaluated using redundancy analysis (RDA), followed by gradient forest analysis applied to plant species abundance data. Soil chemical variables accounted for just over 26% of the total explainable variation in the dataset, followed by bioclimatic variables (19%) and deposition variables (5%), but joint effects between variables also explained a significant portion of the total variation (p < 0.001). Total deposited nitrogen (TDN), and sulphur (TDS) along with bioclimatic and soil chemical variables, were identified as important variables in gradient forest analysis. A single, definitive threshold across TDN was identified at approximately 5.6 kg N ha−1 yr−1 (while a TDS threshold was found at 14.4 kg S ha−1 yr−1). The TDN threshold range was associated primarily with changepoints for several vascular species (Pyrola asarifolia, Pyrola chlorantha, Cornus canadensis, and Arctostaphylos uva-ursi) and bryophyte and lichen species (Pleurozium schreberi, Vulpicida pinastri, and Dicranum polysetum). These results suggest that across Jack pine-dominant forests surrounding the AOSR, the biodiversity-based empirical critical load of nutrient N is 5.6 kg N ha−1 yr−1.

Abstract Understanding movements of Drosophila suzukii (Diptera: Drosophilidae) into berry fruit crops from wild-fruit hosts in borders of semi-natural agroecosystems, such as lowbush blueberry, is important to determining harvesting time and managing wild-fruit diversity near crops. This study aimed to inventory the wild-fruit hosts associated with lowbush blueberry (Ericaceae) production in Québec, Canada, near the limits of lowbush blueberry’s eastern North American range. We also tested the hypothesis that fruit traits of berry fruit species present in or near lowbush blueberry fields might explain field infestation levels. Flies of both sexes emerged from five wild-fruit species in 2016, to which six more species were added in 2017. The most productive wild-fruit hosts were Cornus canadensis (Cornaceae) and Aralia hispida (Araliaceae) (> 100 emerged flies/100 g of fruit) in 2016, to which Prunus pensylvanica (Rosaceae) and Rubus idaeus (Rosaceae) were added in 2017. Among nine variables considered in statistical modelling (fruit size, sugar content, and reflected colour bands) and taxonomic family (a nominal variable), none could explain field infestation levels over two years. In lab tests comparing fruits of Cornus canadensis, a common weed within fields, and lowbush blueberries, mated D. suzukii females laid twice as many eggs on blueberries, but both species were equally suitable for development.

The Siberian Grouse (Falcipennis falcipennis), which is endemic to the “dark-needle” taiga of the Russian Far East, is one of the least studied grouse species in the world. We examined post-breeding habitat selection of Siberian Grouse and contrasted it with that of the better examined Hazel Grouse (Tetrastes bonasia) in two areas near Komsomolsk na Amure, Russia. To infer species-specific preferences, we used field sampling, logistic regression, and AIC model selection, and compared late summer habitats of Siberian Grouse and Hazel Grouse in a mountain- and hilly area in the dark needle taiga. Our study is the first to explain Siberian Grouse habitat relationships with an empirical modelling approach. Results indicate proportions of coniferous/ pioneer trees forest and rejuvenation to be the most important covariates separating Siberian and Hazel Grouse observation sites in forests from both areas. Siberian Grouse tended to select sites with low proportions of pioneer trees and rejuvenation but availability of dwarf shrubs. Bunchberry (Cornus canadensis) appeared to be of high importance for the presence of Siberian Grouse in both regions. Hazel Grouse were common in places dominated by pioneer trees with high canopy cover, and high proportions of grass/herb cover. Hazel Grouse also occurred more often in forest sites with dense vertical layering and rejuvenation. Modern forestry, which results in increasing amounts of forests at younger successional stages, is likely to favour the Hazel Grouse at the expense of the Siberian Grouse.

Although the mining industry provides minerals and metals to the global market and represents important economic opportunities, it also constitutes a major anthropogenic disturbance in the ecosystems where it takes place. However, little is known about its offsite impacts on plant communities. We assessed the frequency and the abundance of five common boreal understorey plant species (Coptis trifolia (L.) Salisb., Cornus canadensis L., Linnaea borealis L., Lysimachia borealis (Raf.) U.Manns & Anderb., and Maianthemum canadense Desf.) at different distances around six mines in Abitibi-Témiscamingue and Nord-du-Québec (Québec). Frequency and (or) abundance of Coptis trifolia and M. canadense decreased near mines, suggesting that they might be sensitive to the loss of forest cover, particle deposition, and soil contamination induced by mining. Conversely, the frequency and abundance of Cornus canadensis increased near active mines, which indicates its resilience to the stress caused by mines and its ability to exploit the niche space left by more sensitive species. No effects on Linnaea borealis and Lysimachia borealis were observed. Our study suggests the possible presence of offsite impacts of mines on plant communities. Further studies considering enigmatic impacts should be conducted in order to develop our understanding of the broader environmental footprint of mining activity.

Veery (Catharus fuscescens) is a breeding migrant thrush that nests throughout much of the temperate forests within Canada. Habitat loss and degradation is thought to be responsible for a steady decline in Veery populations since 1970. We studied habitat characteristics of occupied Veery territories versus unoccupied adjacent areas in southern Ontario during the 2016 breeding season. Occupied territories were characterized as riparian deciduous forests dominated by ash (Fraxinus spp.), Black Cherry (Prunus serotina), and Red Maple (Acer rubrum) trees with an understorey of Balsam Fir (Abies balsamea) and ferns (order Polypodiales); the presence of fruit-producing plants such as Riverbank Grape (Vitis riparia) and Bunchberry (Cornus canadensis) also was important.

ABSTRACT Weed surveys provide the basis for weed management research in lowbush blueberry, but have not been conducted in Nova Scotia since 2001. Documented declines in herbicide efficacy, loss and/or acquisition of herbicide active ingredients, confirmation of herbicide-resistant weed biotypes, and documented vectoring of weed seeds by machinery necessitate a new weed survey. A total of 165 bearing year lowbush blueberry fields were surveyed from 2017 to 2019, within which approximately 211 weed species were identified. Most weed species were herbaceous perennial forbs (89 species) and woody perennials (50 species), followed by annual broadleaf (24 species) and perennial grass weeds (20 species). The remaining flora consisted of a range of ferns, biennials, sedges and rushes, and orchids. The most common weed species were red sorrel (Rumex acetosella L.), poverty oatgrass (Danthonia spicata L. Beauv.), haircap moss (Polytrichum commune Hedw.), hair fescue (Festuca filiformis Pourr.), narrow-leaved goldenrod (Euthamia graminifolia (L) Nutt.), tickle grass (Agrostis hyemalis (Walter) BSP.), woolly panicum (Panicum lanugosum Ell.), cow wheat (Melampyrum lineare Desr.), bunchberry (Cornus canadensis L.), and yellow hawkweed (Hieracium caespitosum Dumort). Increased occurrence of these weed species is likely the result of documented or observed reductions in hexazinone and terbacil efficacy, confirmation of triazine-resistant biotypes, and common occurrence of seeds of these weed species on machinery. Low crop prices have also caused reduced pronamide use, contributing to increased occurrence of hair fescue. Results are guiding future research priorities for weed management in lowbush blueberry.

Abstract The dwarf dogwoods (subgenus Arctocrania) have been widely known to consist of three circumboreal species Cornus suecica, Cornus canadensis, and Cornus unalaschkensis. A fourth putative species was discovered from the northern Myanmar in 1937, but it had never been formally reported on. Here, we formally report the species on the basis of phylogenetic and morphological evidence and name it Cornus wardiana Rushforth & Wahlsteen (sp. nov.). We conducted phylogenetic and morphometric analyses to determine its evolutionary relationship and differentiation from the existing relatives. We dated the phylogeny using molecular data and conducted a biogeographic analysis to gain insights into the evolution and biogeography of the Arctic‐Sino‐Himalayan disjunction. The phylogenetic analysis used sequences of the nrITS and plastid matK and rbcL genes and included all four dwarf dogwoods and 20 other species representing the three other major lineages of Cornus and the outgroup. The morphometric analyses included 60 populations and 102 specimens of dwarf dogwood, representing the entire range of the subgenus. The results showed that C. wardiana diverged first within subgenus Arctocrania in the Miocene, from a wide‐spread ancestor. Results from principal component analysis and discriminant analysis also showed that the Myanmar samples are well separated from the others. Taken together, these results suggest that the dwarf dogwood lineage split from the big‐bracted dogwoods in Asia or Asia‐western North America during the late Paleocene and spread widely to form a Eurasia‐North America distribution; the Arctic‐Sino‐Himalayan disjunction was the result of southward migration in the Miocene followed by extinction in the intervening highland areas.

TFL1homologCorcanTFL1suppresses the initiation of inflorescence development and regulates the inflorescence morphology inCornus canadensis. In flowering plants, there is a wide range of variation of inflorescence morphology. Despite the ecological and evolutionary importance, efforts devoted to the evolutionary study of the genetic basis of inflorescence morphology are far fewer compared to those on flower development. Our previous study on gene expression patterns suggested a CorTFL1-CorAP1 based model for the evolution of determinate umbels, heads, and mini dichasia from elongated inflorescences in Cornus. Here, we tested the function of CorcanTFL1 in regulating inflorescence development in Cornus canadensis through Agrobacterium-mediated transformation. We showed that transgenic plants overexpressing CorcanTFL1 displayed delayed or suppressed inflorescence initiation and development and extended periods of vegetative growth. Transgenic plants within which CorcanTFL1 had been down-regulated displayed earlier emergence of inflorescence and a reduction of bract and inflorescence sizes, conversions of leaves to bracts and axillary leaf buds to small inflorescences at the uppermost node bearing the inflorescence, or phyllotaxy changes of inflorescence branches and leaves from decussate opposite to spirally alternate. These observations support an important role of CorcanTFL1 in determining flowering time and the morphological destinies of leaves and buds at the node bearing the inflorescence. The evidence is in agreement with the predicted function of CorTFL1 from the gene expression model, supporting a key role of CorTFL1 in the evolutionary divergence of inflorescence forms in Cornus.

Abstract In mature buds of the dwarf dogwood lineage (DW) ofCornus, petals and filaments form an “x”‐like box containing mechanical energy from the filaments to allow explosive pollen dispersal. As a start to understand the molecular mechanisms responsible for the origin of this unique structure inCornus, we cloned and characterized the sequences ofAPETALA3(AP3) homologs fromCornus canadensisof the DW lineage and five otherCornusspecies, given the function ofAP3on petal and stamen development inArabidopsis, and tested the function ofCorcanAP3using a stableAgrobacterium‐mediated transformation system. The clonedCorAP3s(AP3‐like genes inCornus) were confirmed to belong to theeuAP3lineage. qRT‐PCR analysis indicated strong increase ofCorcanAP3expression in floral buds of wildtypeC. canadensis. A hairpin construct ofCorcanAP3was successfully introduced into wild type plants ofC. canadensis, resulting in significant reduction ofCorcanAP3expression and abnormal floral development. The abnormal floral buds lost the “x” form and opened immaturely due to delay or retard of petal and stamen elongation and the push of style elongation. The results suggestedCorcanAP3may function to regulate the coordinated rate of development of petals and stamens inC. canadensis, necessary for the x‐structure formation, although the exact molecular mechanism remains unclear. Comparison among sixCornusspecies indicated a greater ratio of stamen to petal and style growth inC. canadensis, suggesting an evolutionary change ofCorAP3expression pattern in the DW lineage, leading to the greater growth of filaments to form the “x”‐box.

BackgroundMany plants of boreal forest of Quebec have been used by Native Americans to treat a variety of microbial infections. However, the antiviral activities of these plants have been seldom evaluated on cellular models to validate their in vitro efficiencies. In this study, Cornus canadensis L. (Cornaceae), a plant used in Native American traditional medicine to treat possible antiviral infections, has been selected for further examination.MethodsThe plant was extracted by decoction and infusion with water, water/ethanol 1:1 and ethanol to obtain extracts similar to those used by Native Americans. The effects of the extracts were tested on herpes simplex virus type-1 (HSV-1) using a plaque reduction assay. Moreover, bioassay-guided fractionation was achieved to isolate bioactive compounds.ResultsWater/ethanol 1:1 infusion of C. canadensis leaves were the most active extracts to inhibit virus absorption with EC50 of about 9 μg mL−1, whereas for direct mode, both extraction methods using water or water/ethanol 1:1 as solvent were relatively similar with EC50 ranging from 11 to 17 μg mL−1. The fractionation led to the identification of active fractions containing hydrolysable tannins. Tellimagrandin I was found the most active compound with an EC50 of 2.6 μM for the direct mode and 5.0 μM for the absorption mode.ConclusionAltogether, the results presented in this work support the antiviral activity of Cornus canadensis used in Native American traditional medicine.

Production of reactive oxygen species (ROS) can be accelerated under various biotic and abiotic stresses causing lipid peroxidation, protein degradation, enzyme inactivation, and DNA damage. Superoxide reductase (SOR) is a novel antioxidant enzyme from Pyrococcus furiosus and is employed by this anaerobic hyperthermophilic archaeon for efficient detoxification of ROS. In this study, SOR was introduced into a flowering plant Cornus canadensis to enhance its heat tolerance and reduce heat induced damage. A fusion construct of the SOR gene and Green Fluorescent Protein gene (GFP) was introduced into C. canadensis using Agrobacterium-mediated transformation. Heat tolerance of the GFP-SOR expressing transgenic plants was investigated by observing morphological symptoms of heat injury and by examining changes in photosynthesis, malondialdehyde (MDA), and proline levels in the plants. Our results indicate that the expression of the P. furiosus SOR gene in the transgenic plants alleviated lipid peroxidation of cell membranes and photoinhibition of PS II, and decreased the accumulation of proline at 40°C. After a series of exposures to increasing temperatures, the SOR transgenic plants remained healthy and green whereas most of the non-transgenic plants dried up and were unable to recover. While it had previously been reported that expression of SOR in Arabidopsis enhanced heat tolerance, this is the first report of the successful demonstration of improved heat tolerance in a non-model plant resulting from the introduction of P. furiosus SOR. The study demonstrates the potential of SOR for crop improvement and that inherent limitations of plant heat tolerance can be ameliorated with P. furiosus SOR.

On Anticosti Island (Quebec, Canada), overbrowsing by white‐tailed deer Odocoileus virginianus has substantially modified plant communities and reduced the recruitment of balsam fir Abies balsamea seedlings over most of the territory. An exception to this phenomenon has been observed in localised patches occurring on a single geological deposit named Chicotte, where the natural recruitment of balsam fir is occurring even in the presence of a large white‐tailed deer population. We hypothesized that edaphic properties within the Chicotte deposit could result in lower forage quality, which in turn could reduce browsing pressure and allow fir regeneration to occur (i.e. bottom—up effects). To test this hypothesis, we measured soil properties and foliage chemistry of four forage species (balsam fir, white spruce Picea glauca, Canada mayflower Maianthemum canadense and Canada bunchberry Cornus canadensis) collected on each of three geological deposits on Anticosti Island: Chicotte, Becscie and Jupiter (the latter two considered as controls). Contrary to expectation, results from principal component analysis suggested that Chicotte was the most fertile, whereas Becsie was the least fertile, of the three deposits. Furthermore, balsam fir foliage chemistry did not respond to geological deposit. Conversely, Mantel et Procrustes tests revealed a significant correlation between soil properties and forage quality for white spruce, consistent with the carbon—nutrient balance hypothesis. Univariate tests confirmed that neutral detergent fiber concentrations in white spruce were higher on the Becscie than on the Chicotte deposit. Likewise, in vitro true digestibility of both white spruce and Canada bunchberry foliage were lower on the Becscie than on the Chicotte deposit. Although we failed to demonstrate why balsam fir recruitment occurs on the Chicotte deposit, our data demonstrate that edaphic properties may affect the quality of some forage types, which potentially affect foraging patterns in overbrowsed boreal landscapes.

An important asset for the management of wild ungulates is recognizing the spatial distribution of forage quality across heterogeneous landscapes. To do so typically requires knowledge of which plant species are eaten, in what abundance they are eaten, and what their nutritional quality might be. Acquiring such data, however, may be difficult and time consuming. Here, we are proposing a rapid and cost-effective forage quality monitoring tool that combines near infrared (NIR) spectra of fecal samples and easily obtained data on plant community composition. Our approach rests on the premise that NIR spectra of fecal samples collected within low population density exclosures reflect the optimal forage quality of a given landscape. Forage quality can thus be based on the Mahalanobis distance of fecal spectral scans across the landscape relative to fecal spectral scans inside exclosures (referred to as DISTEX). The Gi* spatial autocorrelation statistic can then be applied among neighboring DISTEX values to detect and map "hot spots" and "cold spots" of nutritional quality over the landscape. We tested our approach in a heterogeneous boreal landscape on Anticosti Island (Québec, Canada), where white-tailed deer (Odocoileus virginianus) populations over the landscape have ranged from 20 to 50 individuals/km2 for at least 80 years, resulting in a loss of most palatable and nutritious plant species. Our results suggest that hot spots of forage quality occur when old-growth balsam fir stands comprise >39.8% of 300 ha neighborhoods, whereas cold spots occur in laggs (i.e., transition zones from forest to peatland). In terms of ground-level indicator plant species, the presence of Canada bunchberry (Cornus canadensis) was highly correlated with hot spots, whereas tamarack (Larix laricina) was highly correlated with cold spots. Mean DISTEX values were positively and significantly correlated with the neutral detergent fiber and acid detergent lignin contents of feces. While our approach would need more independent field trials before it is fully validated, its low cost and ease of execution should make it a valuable tool for advancing both the basic and applied ecology of large herbivores.

Hassan, H. M., Jiang, Z.-H., Asmussen, C., McDonald, E. and Qin, W. 2014. Antibacterial activity of northern Ontario medicinal plant extracts. Can. J. Plant Sci. 94: 417–424. In the present study, the antibacterial activity (in vitro) of the leaf and/or flower crude extracts of Anaphalis margaritacea (L.) Benth & Hook.f., Grindelia squarrosa (Pursh) Dunal, Apocynum androsaemifolium L., Arctostaphylos uva-ursi (L.) Spreng, Cornus canadensis L. and Xanthium strumarium L. medicinal plants was analyzed through the hole-plate diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays against Escherichia coli, Aeromonas caviae, Paenibacillus alvei, Micrococcus luteus, Mycobacterium avium subsp. avium and Bacillus cereus bacteria. In addition, the time-kill dynamic processes of these extracts against A. caviae, B. cereus, P. alvei, and M. luteus bacteria were also tested. The leaf and flower extracts of Anap. margaritacea and G. squarrosa possess significant antibacterial activity against all the bacteria tested, with inhibition of A. caviae, P. alvei and M. luteus within 1–12 h of incubation at MBC. Particularly, at higher concentrations of the Anap. margaritacea flower crude extract (2–3×MBC), inhibition of A. caviae, B. cereus, P. alvei, and M. luteus bacteria is achieved between 0.5 and 4 h of incubation. In addition, these extracts exhibit high inhibition diameters (majority > 18 mm) and low MIC and/or MBCs (majority=1.25 mg mL−1). In contrast, the leaf extracts of Arct. uva-ursi, X. strumarium, Apoc. androsaemifolium and C. canadensis plants demonstrate moderate to low activity. These results indicate that extracts from Anap. margaritacea and G. squarrosa could be a source of novel antimicrobial scaffolds, compounds or pharmacophores with implications in the pharmaceutical industry and medicine.

Blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae), is the most important pest of blueberries in eastern North America. Insecticide use in fruit-bearing lowbush blueberry fields could be reduced with management strategies focused on vegetative fields. Fly distribution and fruit infestation levels were assessed where fruit-bearing and vegetative fields adjoin and along forested edges of vegetative fields. Along adjoining edges, immature female flies were captured in fruiting fields and mature females in vegetative fields throughout the season. Male fly captures and fruit infestation levels were greater at 5 m than at 30 m from the edge. Along forested edges, fly captures were best predicted by densities of ripe lowbush blueberries and large coniferous trees. Maggot infestation level in lowbush blueberries was best predicted by blueberry density and small deciduous trees. Bunchberry, Cornus canadensis L., was the only non-crop host in which blueberry maggot was found. We have shown that relatively high numbers of flies occur in vegetative fields and at edges of fruiting fields. Ripe blueberries and certain vegetation in forested edges affect fly distribution and probably maintain populations. These results may help to predict where controls for blueberry maggot should be targeted and suggest that management strategies focused on vegetative fields and field edges may be worthwhile.

BackgroundTranscriptome sequencing analysis is a powerful tool in molecular genetics and evolutionary biology. Here we report the results of de novo 454 sequencing, characterization, and comparison of inflorescence transcriptomes of two closely related dogwood species, Cornus canadensis and C. florida (Cornaceae). Our goals were to build a preliminary source of genome sequence data, and to identify genes potentially expressed differentially between the inflorescence transcriptomes for these important horticultural species.ResultsThe sequencing of cDNAs from inflorescence buds of C. canadensis (cc) and C. florida (cf), and normalized cDNAs from leaves of C. canadensis resulted in 251799 (ccBud), 96245 (ccLeaf) and 114648 (cfBud) raw reads, respectively. The de novo assembly of the high quality (HQ) reads resulted in 36088, 17802 and 21210 unigenes for ccBud, ccLeaf and cfBud. A reference transcriptome for C. canadensis was built by assembling HQ reads of ccBud and ccLeaf, containing 40884 unigenes. Reference mapping and comparative analyses found 10926 sequences were putatively specific to ccBud, and 6979 putatively specific to cfBud. Putative differentially expressed genes between ccBud and cfBud that are related to flower development and/or stress response were identified among 7718 shared sequences by ccBud and cfBud. Bi-directional BLAST found 87 (41.83% of 208) of Arabidopsis genes related to inflorescence development had putative orthologs in the dogwood transcriptomes. Comparisons of the shared sequences by ccBud and cfBud yielded 65931 high quality SNPs between two species. The twenty unigenes with the most SNPs are listed as potential genetic markers for evolutionary studies.ConclusionsThe data provide an important, although preliminary, information platform for functional genomics and evolutionary developmental biology in Cornus. The study identified putative candidates potentially involved in the genetic regulation of inflorescence evolution and/or disease resistance in dogwoods for future analyses. Results of the study also provide markers useful for dogwood phylogenomic studies.

KEY MESSAGE : Efficient Agrobacterium -mediated genetic transformation for investigation of genetic and molecular mechanisms involved in inflorescence architectures in Cornus species. Cornus canadensis is a subshrub species in Cornus, Cornaceae. It has recently become a favored non-model plant species to study genes involved in development and evolution of inflorescence architectures in Cornaceae. Here, we report an effective protocol of plant regeneration and genetic transformation of C. canadensis. We use young inflorescence buds as explants to efficiently induce calli and multiple adventitious shoots on an optimized induction medium consisting of basal MS medium supplemented with 1mg/l of 6-benzylaminopurine and 0.1mg/l of 1-naphthaleneacetic acid. On the same medium, primary adventitious shoots can produce a large number of secondary adventitious shoots. Using leaves of 8-week-old secondary shoots as explants, GFP as a reporter gene controlled by 35S promoter and hygromycin B as the selection antibiotic, a standard procedure including pre-culture of explants, infection, co-cultivation, resting and selection has been developed to transform C. canadensis via Agrobacterium strain EHA105-mediated transformation. Under a strict selection condition using 14mg/l hygromycin B, approximately 5% explants infected by Agrobacterium produce resistant calli, from which clusters of adventitious shoots are induced. On an optimized rooting medium consisting of basal MS medium supplemented with 0.1mg/l of indole-3-butyric acid and 7mg/l hygromycin B, most of the resistant shoots develop adventitious roots to form complete transgenic plantlets, which can grow normally in soil. RT-PCR analysis demonstrates the expression of GFP transgene. Green fluorescence emitted by GFP is observed in transgenic calli, roots and cells of transgenic leaves under both stereo fluorescence microscope and confocal microscope. The success of genetic transformation provides an appropriate platform to investigate the molecular mechanisms by which the various inflorescence forms are developed in Cornus plants.

Despite increasing interest in the molecular mechanisms of floral diversity, few studies have investigated the developmental and genetic bases of petaloid bracts. This study examined morphological patterns of bract initiation and expression patterns of B-class MADS-box genes in bracts of several Cornus species. We suggest that petaloid bracts in this genus may not share a single evolutionary origin. Developmental pathways of bracts and spatiotemporal expression of B-class genes in bracts and flowers were examined for four closely related dogwood species. Divergent morphological progressions and gene expression patterns were found in the two sister lineages with petaloid bracts, represented by Cornus florida and Cornus canadensis. Phylogeny-based analysis identified developmental and gene expression changes that are correlated with the evolution of petaloid bracts in C. florida and C. canadensis. Our data support the existence of independent evolutionary origins of petaloid bracts in C. canadensis and C. florida. Additionally, we suggest that functional transference within B-class gene families may have contributed to the origin of bract petaloidy in C. florida. However, the underlying mechanisms of petaloid bract development likely differ between C. florida and C. canadensis. In the future this hypothesis can be tested by functional analyses of Cornus B-class genes.

We explored interactions among plant growth forms in the understory of mature boreal mixedwood forests in western Canada by investigating the competitive influence of erect shrubs on herbs (forbs and grasses). We established 10 pairs of plots; all erect shrubs were removed in one plot of each pair (removals) and left intact in the other plot (controls). Two years later, we harvested all aboveground biomass of the herbaceous layer (herb biomass: this included graminoids, forbs, trailing shrubs, and species with a woody base but not woody stems) from the 20 plots. We tested for significant differences in understory species biomass and composition between control and removal plots and examined the influence of 25 environmental factors on species composition of the herbaceous layer. Competition intensity was measured by the natural logarithm of response ratio (ln RR) index based on herb biomass. After erect shrub removal, there was a significant increase in herb biomass, mostly due to an increase of the most common species (e.g., Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). The values of competition intensity (ln RR) varied among herb species but were, overall, positive, indicating a release from competition following shrub removal. Composition of the herbaceous layer was significantly different between removal and control plots and was also significantly related to seven environmental factors, which explained 40% of the variation in composition. Our study suggests that there is asymmetric competition for light between erect shrub and herb species in boreal ecosystems.

This was the first study to have surveyed the spatial and temporal structure of Apocrita wasps in lowbush blueberry fields, a unique native agricultural landscape in Maine and eastern Canada. The relative abundances of wasps associated with lowbush blueberry (Vaccinium angustifolium Ait.) were investigated in 33 blueberry fields throughout Washington County, Maine, USA. Native wasps were captured during the springs and summers of 1997 and 1998 in Malaise traps erected along a transect in each field. Vegetation sampling was also conducted along these transects to quantify available floral resources. Data indicate the abundance of the total wasp community was positively associated with the abundance of sheep laurel (Kalmia angustifolia L.). Relationships between trap capture of 13 wasp morphospecies and other flowering weeds were also investigated. Most taxa in 1998 were positively associated with one or more of the following flowering plants: bunchberry (Cornus canadensis L.), bush honeysuckle (Diervilla lonicera P. Mill.), dogbane (Apocynum androsaemifolium L.), sheep laurel, and witherod (Viburnum nudum var. cassinoides L.). Similar results were not evident in 1997 because the method used to sample vegetation was not as extensive as that used in 1998. However, sheep laurel was positively associated with the wasp genera Microplitis spp. and Phanerotoma spp. during both years.