Jacques Brisson

Clinical spectrum of bronchogenic cysts of the mediastinum and lung in the adult

Bronchogenic cysts are closed sacs considered to be the result of an abnormal budding of the respiratory system. They are lined by ciliated epithelium and have focal areas of hyaline cartilage, smooth muscle, and bronchial glands within their walls. They are seldom seen in the adult, and most are thought to be asymptomatic and free of complications. During a 20-year period, 86 patients underwent resection of a bronchogenic cyst of the mediastinum (66 patients) and lung (20 patients). There were 47 women and 39 men whose ages ranged from 16 to 69 years. Seventy-two percent of patients (67% with mediastinal cysts and 90% with cysts of the lung) were symptomatic at the time of operation, and the majority had two or more symptoms. Despite extensive investigations, which in some cases included computed tomographic scanning (n = 12) and angiography (n = 22), a positive diagnosis was never made preoperatively even if it was suspected in 57% of patients. In nearly all patients, the operative approach was that of a posterolateral thoracotomy. All but two mediastinal bronchogenic cysts could be locally excised, but all bronchogenic cysts of the lung required pulmonary resection (lobectomy, 13; limited resection, 6; pneumonectomy, 1). Major operative difficulties were encountered in 35 patients, all of whom were symptomatic preoperatively. Thirty-three patients had a complicated cyst; the complications consisted of fistulization (n = 16), ulcerations of the cyst wall (n = 13), hemorrhage (n = 2), infection without fistulization (n = 1), and secondary bronchial atresia (n = 1). Overall, 82% of patients had a bronchogenic cyst that was either symptomatic or complicated or both.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximizing pollutant removal in constructed wetlands: Should we pay more attention to macrophyte species selection?

While the positive role of macrophytes on removal efficiency in constructed wetlands has been well established, possible differences in performance between plants species of comparable life forms and sizes are much harder to demonstrate. We reviewed 35 experimental studies published in peer-reviewed journals and proceedings on the effect of macrophyte species selection on pollutant removal in SSFCW. The studies cover a wide range of macrophyte species, experimental approaches (from well-replicated microcosm experiments to comparison between full full-size constructed wetlands), climatic conditions (from tropical to cold-temperate) and types of effluent (domestic, industrial, etc.). Frequent methodological limitations in these studies compel caution in the interpretation of their results. Yet, the fact that the majority found some (occasionally large) differences in efficiency between plant species for one or more type of pollutant suggests that macrophyte species selection does matter. However, there is little generalization to be made that could help guide species selection for SSFCW, except for the exact conditions in which the experiments were done. For example, the same pair of species that was tested in different studies occasionally gave opposite results in terms of which one performs best. Also, most studies provided few insights on the mechanisms or plant properties that could explain the observed differences in plant species efficiency. Finally, we discuss other relevant research questions and approaches that could help better guide macrophyte species selection for CW.

Nitrogen transformations and retention in planted and artificially aerated constructed wetlands

Nitrogen (N) processing in constructed wetlands (CWs) is often variable, and the contribution to N loss and retention by various pathways (nitrification/denitrification, plant uptake and sediment storage) remains unclear. We studied the seasonal variation of the effects of artificial aeration and three different macrophyte species (Phragmites australis, Typha angustifolia and Phalaris arundinacea) on N processing (removal rates, transformations and export) using experimental CW mesocosms. Removal of total nitrogen (TN) was higher in summer and in planted and aerated units, with the highest mean removal in units planted with T. angustifolia. Export of ammonium (NH(4)(+)), a proxy for nitrification limitation, was higher in winter, and in unplanted and non-aerated units. Planted and aerated units had the highest export of oxidized nitrogen (NO(y)), a proxy for reduced denitrification. Redox potential, evapotranspiration (ETP) rates and hydraulic retention times (HRT) were all predictors of TN, NH(4)(+) and NO(y) export, and significantly affected by plants. Denitrification was the main N sink in most treatments accounting for 47-62% of TN removal, while sediment storage was dominant in unplanted non-aerated units and units planted with P. arundinacea. Plant uptake accounted for less than 20% of the removal. Uncertainties about the long-term fate of the N stored in sediments suggest that the fraction attributed to denitrification losses could be underestimated in this study.

The Effect of Neighbors on Root Distribution in a Creosotebush (Larrea Tridentata) Population

We excavated and mapped the lateral extension of 32 creosotebush shrubs (Larrea tridentata) in the Chihuahuan desert of New Mexico to examine the effect of neighborhood interaction on root distribution. The smallest closed—angle polygon encompassing all roots of an individual was taken as a representation of its root system. Several geometrical characteristics of these polygons were measured and compared to interference vectors based on the location and size of the neighbors. We found that root systems were more developed away from the maximum competitive pressure of neighbors. Relation between root system shape and pressure from neighbors was stronger when the competitive vectors were integrating effect from all neighbors. Size of neighbors did not appear to contribute significantly to the relation. The resulting spatial pattern tended to reduce the overlap between neighboring root systems. Two conceptual models of root growth response to neighbors appear to explain our results. Both models assume that when the root system of neighbors meet, root growth is impaired or ceases at the zone of contact. In the nonoverlapping, non—compensatory model, the decrease in root growth between two close neighbors in not compensated elsewhere, possibly affecting the overall plant performance. In the non—overlapping, compensatory model, a plant with a close neighbor responds by investing in root growth away from the competitive pressure or simply in zones free of neighbors. Under this model, two plants can be close to each other and not compete. Competition in the population is for space and only occurs when a plant root system is crowded on all sides.

Plant functional group identity and diversity determine biotic resistance to invasion by an exotic grass

Summary 1. Biotic resistance, the ability of species in a community to limit invasion, is central to our understanding of how communities at risk of invasion assemble after disturbances, but it has yet to translate into guiding principles for the restoration of invasion-resistant plant communities. We combined experimental, functional, and modelling approaches to investigate processes of community assembly contributing to biotic resistance to an introduced lineage of Phragmites australis, a model invasive species in North America. We hypothesized that (i) functional group identity would be a good predictor of biotic resistance to P. australis, while species identity effect would be redundant within functional group (ii) mixtures of species would be more invasion resistant than monocultures. 2. We classi! ed 36 resident wetland plants into four functional groups based on eight functional traits. We conducted two competition experiments based on the additive competition design with P. australis and monocultures or mixtures of wetland plants. As an indicator of biotic resistance, we calculated a relative competition index (RCIavg) based on the average performance of P. australis in competition treatment compared with control. To explain diversity effect further, we partitioned it into selection effect and complementarity effect and tested several diversity‐interaction models. 3. In monoculture treatments, RCIavg of wetland plants was signi! cantly different among functional groups, but not within each functional group. We found the highest RCIavg for fast-growing annuals, suggesting priority effect. 4. RCIavg of wetland plants was signi! cantly greater in mixture than in monoculture mainly due to complementarity‐diversity effect among functional groups. In diversity‐interaction models, species interaction patterns in mixtures were described best by interactions between functional groups when ! tted to RCIavg or biomass, implying niche partitioning. 5. Synthesis. Functional group identity and diversity of resident plant communities are good indicators of biotic resistance to invasion by introduced Phragmites australis, suggesting niche preemption (priority effect) and niche partitioning (diversity effect) as underlying mechanisms. Guiding principles to understand and/or manage biological invasion could emerge from advances in community theory and the use of a functional framework. Targeting widely distributed invasive plants in different contexts and scaling up to ! eld situations will facilitate generalization.

Greenhouse gas production and efficiency of planted and artificially aerated constructed wetlands

Greenhouse gas (GHG) emissions by constructed wetlands (CWs) could mitigate the environmental benefits of nutrient removal in these man-made ecosystems. We studied the effect of 3 different macrophyte species and artificial aeration on the rates of nitrous oxide (N(2)O), carbon dioxide (CO(2)) and methane (CH(4)) production in CW mesocosms over three seasons. CW emitted 2-10 times more GHG than natural wetlands. Overall, CH(4) was the most important GHG emitted in unplanted treatments. Oxygen availability through artificial aeration reduced CH(4) fluxes. Plant presence also decreased CH(4) fluxes but favoured CO(2) production. Nitrous oxide had a minor contribution to global warming potential (GWP<15%). The introduction of oxygen through artificial aeration combined with plant presence, particularly Typha angustifolia, had the overall best performance among the treatments tested in this study, including lowest GWP, greatest nutrient removal, and best hydraulic properties.

Roadside as Invasion Pathway for Common Reed (Phragmites australis)

Abstract The rapid progression of an invasive genotype of common reed along roads and other linear infrastructures in North America provides one of the most spectacular examples of the role of transportation corridors as invasion pathways. In this paper, we discuss ecological patterns and processes in roadside habitats important for understanding the invasion dynamics of common reed from coastal areas inland. Frequent disturbances in roadsides combined with potentially high levels of nutrients from adjacent land and stress conditions (from deicing salt and other pollutants) mimic the conditions unfortunately found more and more in natural wetlands. The novel contribution of roads is the creation of linear wetlands with an unprecedented level of connectivity. Genetic evidence shows that invasion inland coincides with the intensification of the road network. Time series analysis of remote sensing data reveals impressive rates of invasion of roadsides and other linear infrastructures, suggesting prime conditions for common reed in these novel habitats. Whereas reed dispersal along roads was thought to be largely due to rhizome transport, new evidence suggests a significant contribution of sexual reproduction and seedling establishment, likely enhanced by climate warming at northern latitudes. There is little evidence that other wetland plants can slow down vegetative expansion of common reed in roadside habitats, but plant cover could prevent seedling establishment and shading by shrubs and trees limit lateral clonal expansion. The fact that common reed possibly provides water treatment and other ecosystem services in roadsides must be carefully weighed against the threat to biodiversity in natural systems. All this begs for investigating urgently if, where, and how we should intervene without compromising the great value of wetlands of conservation interest intersected by roads. Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud

Beech-maple dynamics in an old-growth forest in southern Québec, Canada

AbstractA study of forest succession was conducted in an 11 ha old-growth beech-maple stand located at the northern limit of the temperate deciduous forest of North America. Eventual changes in dominance were simulated from three transition matrix models based on understory composition or observed replacement in forest gaps. All the models suggested that the forest composition is not currently at equilibrium. If the transition tendency persists, American beech (Fagus grandifolia Ehrh.) will sharply increase in abundance at the expense of sugar maple (Acer saccharum Marsh.). Possible mechanisms responsible for this replacement are discussed.

Evidence of sexual reproduction in the invasive common reed (Phragmites australis subsp. australis; Poaceae) in Eastern Canada: a possible consequence of global warming?

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is native to North America and has always been a minor component of wetlands. However, this species has undergone a rapid expansion in the northeastern United States and Canada during the last century, to the point of becoming a nuisance in some areas (Mal and Narine 2004). At its northern limit in eastern Canada, it is particularly invasive in canals, waterways, roadside ditches, and wetlands (Hudon et al. 2005; Lavoie et al. 2003). There is increasing evidence that this recent expansion was a consequence of the introduction of a European genotype (haplotype M) in the 19th and 20th century (Lelong et al. 2007; Saltonstall 2002). The invasive European haplotype has been designated as P. australis (Cav.) Trin. ex Steud. subsp. australis, while the native haplotype is now referred to as P. australis (Cav.) Trin. ex Steud. subsp. americanus Saltonstall, P.M. Peterson & Soreng (Saltonstall et al. 2004). Several morphological characteristics such as basal internode color, glume length, and inflorescence morphology have been used to distinguish between the native and introduced subspecies in the field (Catling 2006, 2007). In eastern Canada, range expansion of Phragmites has been entirely attributed to vegetative reproduction since no seedlings (from either the native or the exotic variety) had ever been reported in the field (Dore and McNeil 1980; Gervais et al. 1993; Grandtner 1999; Small and Catling 2001). Dore and McNeil (1980, pg.167) stated that ‘‘no sound grains are known to be formed’’ in southern Ontario, and that the condensed nature of the clones and their RHODORA, Vol. 110, No. 942, pp. 225–230, 2008 E Copyright 2008 by the New England Botanical Club

In the past two centuries, human activities have caused major changes in the tree species composition of southern Québec, Canada

Abstract We compared the presettlement forest composition of 60 lots of southern Québec, as reconstructed from wood sales reported in old notary deeds, with their present day composition. Some tree species, such as sugar maple (Acer saccharum) and ash (Fraxinus americana and/or F. pennsylvanica), have shown important increases since European colonization, while others have decreased sharply. In a site-by-site comparison, there are many instances where a species sold from a particular lot is completely absent from this lot today. Tamarack (Larix laricina) and black spruce (Picea mariana), two species that appear in the notary deeds, were completely eliminated from the studied lots. The apparent discrepancy between the predominance of lowlands in the landscape and the low presence in the notary deeds of tree species that prefer more humid conditions suggests that precolonial forests on the clay plain and lowlands were sparse or patchy or were composed of tree species of little stature or commercial value. For mesic sites, sales reported in the notary deeds suggest that the presettlement forest in the Haut-Saint-Laurent region corresponded to the maple-beech-birch forest type and that the most important change since European settlement is a loss or decrease in the abundance of American beech (Fagus grandifolia) and yellow birch (Betula alleghaniensis). In this agro-forested landscape, there is no indication of an eventual return toward the original forest composition, nor should we expect one considering the extent and the irreversible nature of some of the ecosystem modifications caused by human activity.