Personne : Lapointe, Line
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Université Laval. Département de biologie
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Publication Accès libreInvader disruption of belowground plant mutualisms reduces carbon acquisition and alters allocation patterns in a native forest herb(Wiley-Blackwell Publishing Ltd, 2015-10-27) Hale, Alison N.; Lapointe, Line; Kalisz, SusanInvasive plants impose novel selection pressures on naïve mutualistic interactions between native plants and their partners. As most plants critically rely on root fungal symbionts (RFSs) for soil resources, invaders that disrupt plant–RFS mutualisms can significantly depress native plant fitness. Here, we investigate the consequences of RFS mutualism disruption on native plant fitness in a glasshouse experiment with a forest invader that produces known anti‐fungal allelochemicals. Over 5 months, we regularly applied either green leaves of the allelopathic invader Alliaria petiolata, a nonsystemic fungicide to simulate A. petiolata's effects, or green leaves of nonallelopathic Hesperis matronalis (control) to pots containing the native Maianthemum racemosum and its RFSs. We repeatedly measured M. racemosum physiology and harvested plants periodically to assess carbon allocation. Alliaria petiolata and fungicide treatment effects were indistinguishable: we observed inhibition of the RFS soil hyphal network and significant reductions in M. racemosum physiology (photosynthesis, transpiration and conductance) and allocation (carbon storage, root biomass and asexual reproduction) in both treatments relative to the control. Our findings suggest a general mechanistic hypothesis for local extinction of native species in ecosystems challenged by allelopathic invaders: RFS mutualism disruption drives carbon stress, subsequent declines in native plant vigor, and, if chronic, declines in RFS‐dependent species abundance. Publication Accès libreSlow responses of understory plants of maple-dominated forests to white-tailed deer experimental exclusion(Elsevier, 2010-07-30) Côté, Steeve D.; Lapointe, Line; Ouellet, Jean-Pierre; Collard, Amélie; Crête, Michel; Lussier, Alain; Daigle, ClaudeWe examined the response of understory plants in mature maple-dominated forests of southern Québec, Canada, following about 30 years of high deer densities, using a deer exclosure experiment. An exclosure and a paired control of 625 m2 each were established on six sites in 1998. An exclosure and a paired control of 16 m2 were added at each of the same sites in 2003 but under a recent canopy gap to determine if light could enhance plant responses. We measured plant richness and abundance, and aboveground biomass of different plant groups for 8 years in the understory plots and for 3 years in the canopy gaps. Four herbaceous species were also monitored individually in the same plots. No significant differences between treatments were found in plots under forest cover, except for lateral obstruction at 0–50 cm height which was higher in the exclosures. Under canopy gaps, however, tree seedling and total plant abundance were higher in deer exclosures than in control plots. Trillium erectum recovered partially as individuals were taller, had larger leaves and more frequently produced a flower or a fruit in the absence of deer browsing under forest cover. To a lesser extent, Erythronium americanum and Maianthemum canadense also exhibited signs of recovery but were still at the single-leaf stage after 8 years of recovery. In general, the different plant groups exhibited little recovery following deer exclusion, possibly because of the low light levels that prevailed in the understory of undisturbed maple-dominated forests. The higher latitude of the present study could also contribute to the slow recovery rates of the different groups of plants compared to studies conducted in northeastern USA. Variability among sites and years had an effect on detection of statistically significant differences. Trends are however appearing over time, suggesting that many understory plants are recovering very slowly following deer exclusion. Our results emphasize the importance of studying large herbivore–forest interactions on different groups of plants, but also on specific species, and under different latitudes to be fully understood. Publication Accès libreCloudberry cultivation in cutover peatland : improved growth on less decomposed peat.(Agricultural Institute of Canada, 2015-05-01) Rochefort, Line; Lapointe, Line; Bussières, JulieLa culture de la chicouté est sérieusement évaluée comme une option de réhabilitation des tourbières après récolte de la tourbe à des fins horticoles. Outre le gain en termes de valeur écologique et économique de ces sites, la culture de la chicouté pourrait augmenter le rendement en fruits et faciliter la récolte des fruits par rapport à la récolte en tourbières naturelles. Des études antérieures ont montré une croissance initiale lente qui a été provisoirement attribuée aux caractéristiques du substrat. Des expériences sur le terrain et en serres ont donc été mises en place pour mieux caractériser l'effet de différents substrats combinée aux techniques de restauration, sur la croissance des clones mâles et femelles. La chicouté a présenté une meilleure croissance en tourbe fibrique moins décomposée (H1–H3) qu'en tourbe mésique plus décomposée. La restauration devrait donc précéder la mise en culture de la chicouté de quelques années, afin de planter les rhizomes dans la couche de tourbe fibrique nouvellement accumulée. Les clones mâles produisent des feuilles plus grandes et plus de ramets par rhizome que les clones femelles en conditions communes de croissance. Les différences observées entre les sexes sont donc d'ordre génétique plutôt qu'environnemental. De plus, nous avons observé que les clones semblent particulièrement sensibles à la présence d'aluminium. En conclusion, le niveau de décomposition de la tourbe apparaît comme un des facteurs déterminant le succès de plantations de chicouté. Publication Accès libreReintroduction of salt marsh vegetation and phosphorus fertilisation improve plant colonisation on seawater-contaminated cutover bogs(International Mire Conservation Group, 2016-01-01) Hogue-Hugron, Sandrine; Émond, Catherine; Rochefort, Line; Lapointe, LineCoastal bogs that are used for peat extraction are prone to contamination by seawater during storm events. Once contaminated, they remain mostly bare because of the combination of high salinity, low pH, high water table and low nutrient availability. The goal of this research was to investigate how plant colonisation at salt-contaminated bogs can be accelerated, in order to prevent erosion and fluvial export of the peat. At two seawater-contaminated bogs, we tested the application of rock phosphate and dolomitic lime in combination with five plant introduction treatments&58; transplantation of Carex paleacea&59; transplantation of Spartina pectinata&59; transfer of salt marsh diaspores in July&59; transfer of salt marsh diaspores in August&59; and no treatment (control). The effects of different doses of lime on the growth of C. paleacea and S. pectinata were also investigated in a greenhouse experiment. In the field, phosphorus fertilisation improved plant growth. Transplantation of C. paleacea resulted in the highest plant colonisation, whereas salt marsh diaspore transfer led to the highest species diversity. Lime applications did not improve plant establishment in either the field or the greenhouse. To promote revegetation of seawater-contaminated cutover bogs, adding P is an asset, Carex paleacea is a good species to transplant, and the transfer of salt marsh diaspores improves plant diversity. Publication Accès libreFertilizers stimulate root production in cloudberry (Rubus chamaemorus) rhizomes transplanted in a cutover peatland(Canadian Science Publishing, 2017-04-25) Boulanger Pelletier, Jade; Lapointe, LineCloudberry has good economic potential for Canada, but crop practices must be improved before commercial production can be established. Transplants usually consist of rhizome segments collected in natural populations; however, the very low root density of these transplants might partly explain their initial slow growth and high mortality. The objective of this study was to determine the effects of mineral fertilization and auxin applications on root initiation and elongation. Three N–P–K fertilization treatments were applied at the planting of bare rhizomes in peatlands, while auxin applications were tested in both greenhouse and field experiments. Roots of fertilized plants were two to four times longer and more numerous than those of control plants after one complete growing season but fertilization did not lead to early rooting. Rhizome segments produced new shoots before investing in root production, suggesting that rhizome carbohydrate reserves are not sufficient to allow both the shoot and root to be produced at the same time. Auxin applications to the rhizomes incurred high mortality and did not stimulate root production in both the field and greenhouse experiments. We conclude that fertilizers applied at planting can improve cloudberry initial survival rate, rooting, and early shoot growth, which could eventually lead to improved plant cover and fruit yield. Publication Accès libreLate canopy closure delays senescence and promotes growth of a spring ephemeral, Allium tricoccum(Canadian Science Publishing, 2017-02-13) Lapointe, Line; Bussières, Julie; Dion, Pierre-PaulSpring ephemerals take advantage of the high light conditions in spring to accumulate carbon reserves through photosynthesis before tree leaves unfold. Recent work has reported delayed leaf senescence under constant light availability in some spring ephemerals, such as wild leek (Allium tricoccum). This paper aims to establish whether tree canopy composition and phenology can influence the growth of spring ephemerals through changes in their phenology. Wild leek bulbs were planted in 31 plots in southern Quebec, Canada, under canopies varying in composition and densities. Light availability and tree phenology were measured, along with other environmental conditions, and their effect on the growth of wild leeks was assessed with a redundancy analysis. Higher light availability resulted in better growth of wild leeks. The plants postponed their senescence under trees with late bud-burst, and thus better bulb growth and seed production were achieved. The tree litter and temperature and moisture levels of the soil also influenced the growth and survival of wild leeks. Thus, tree leaf phenology appears to have a strong impact on the growth of spring ephemerals by modulating the length of their growing season and their photosynthetic capacity. This underlines the importance of considering the variation of light availability throughout the growing season in the study of spring ephemerals. Publication Accès libreLight acclimation strategies change from summer green to spring ephemeral as wild-leek plants age(Botanical Society of America, 2016-05-13) Lapointe, Line; Brisson, Jacques; Dion, Pierre-Paul; Fontaine, BastienPREMISE OF THE STUDY : Spring‐ephemeral forest‐herbs emerge early to take advantage of the high‐light conditions preceding canopy closure; they complete their life cycle in a few weeks, then senesce as the tree canopy closes. Summer greens acclimate their leaves to shade and thus manage to maintain a net carbon gain throughout summer. Differences in phenology among life stages within a species have been reported in tree saplings, whose leaf activity may extend beyond the period of shade conditions caused by mature trees. Similar phenological acclimation has seldom been studied in forest herbs. METHODS : We compared wild‐leek bulb growth and leaf phenology among plants from seedling to maturity and from under 4 to 60% natural light availability. We also compared leaf chlorophyll content and chl a/b ratio among seedlings and adult plants in a natural population as an indicator of photosynthetic capacity and acclimation to light environment. KEY RESULTS : Overall, younger plants senesced later than mature ones. Increasing light availability delayed senescence in mature plants, while hastening seedling senescence. In natural populations, only seedlings acclimated to the natural reduction in light availability through time. CONCLUSIONS : Wild‐leek seedlings exhibit a summer‐green phenology, whereas mature plants behave as true spring ephemerals. Growth appears to be more source‐limited in seedlings than in mature plants. This modulation of phenological strategy, if confirmed in other species, would require a review of the current classification of species as either spring ephemerals, summer greens, wintergreens, or evergreens. Publication Accès libreThermal acclimation of leaf respiration as a way to reduce source-sink imbalance at low temperature in Erythronium americanum, a spring ephemeral.(Canadian Science Publishing, 2017-11-14) Dong, Yanwen; Gérant, Dominique; Lapointe, LineMany spring geophytes exhibit greater growth at colder than at warmer temperatures. Previous studies have suggested that there is less disequilibrium between source and sink activity at low temperatures, which delays leaf senescence and leads to higher accumulation of biomass in the perennial organ. We hypothesized that dark respiration acclimates to temperature at both the leaf and bulb levels, mainly via the alternative respiratory pathway, as a way to reduce source–sink imbalance. Erythronium americanum Ker-Gawl. was grown under three temperature regimes: 8/6 °C, 12/8 °C, and 18/14 °C (day/night). Plant respiratory rates were measured at both growth and common temperatures to determine whether differences were due to the direct effects of temperature on respiratory rates or to acclimation. Leaf dark respiration exhibited homeostasis, which together with lower assimilation at low growth temperature, most likely reduced the quantity of C available for translocation to the bulb. No temperature acclimation was visible at the sink level. However, bulb total respiration varied through time, suggesting potential stimulation of bulb respiration as sink limitation builds up. In conclusion, acclimation of respiration at the leaf level could partly explain the better equilibrium between source and sink activity in plants grown in low-temperatures, whereas bulb respiration responds to source–sink imbalance. Publication Accès libreResponses of two understory herbs, Maianthemum canadense (Liliaceae) and Eurybia macrophylla (Asteraceae), to experimental forest warming : early emergence is the key to enhanced reproductive output.(Wiley, 2015-10-08) Lapointe, Line; Rice, Karen E.; Jacques, Marie-Hélène; Montgomery, Rebecca A.; Stefanski, Artur; Reich, PeterPREMISE OF THE STUDY : Understory herbs might be the most sensitive plant form to global warming in deciduous forests, yet they have been little studied in the context of climate change. METHODS : A field experiment set up in Minnesota, United States simulated global warming in a forest setting and provided the opportunity to study the responses of Maianthemum canadense and Eurybia macrophylla in their natural environment in interaction with other components of the ecosystem. Effects of +1.7° and +3.4°C treatments on growth, reproduction, phenology, and gas exchange were evaluated along with treatment effects on light, water, and nutrient availability, potential drivers of herb responses. KEY RESULTS : Overall, growth and gas exchanges of these two species were modestly affected by warming. They emerged up to 16 (E. macrophylla) to 17 d (M. canadense) earlier in the heated plots than in control plots, supporting early‐season carbon gain under high light conditions before canopy closure. This additional carbon gain in spring likely supported reproduction. Eurybia macrophylla only flowered in the heated plots, and both species had some aspect of reproduction that was highest in the +1.7°C treatment. The reduced reproductive effort in the +3.4°C plots was likely due to reduced soil water availability, counteracting positive effects of warming. CONCLUSIONS : Global warming might improve fitness of herbaceous species in deciduous forests, mainly by advancing their spring emergence. However, other impacts of global warming such as drier soils in the summer might partly reduce the carbon gain associated with early emergence. Publication Accès libreLinkage between exotic earthworms, understory vegetation and soil properties in sugar maple forests(Elsevier, 2016-01-18) Drouin, Mélanie; Lapointe, Line; Bradley, RobertThe comminuting and soil mixing activities of earthworms can affect soil physical, chemical and biolog-ical properties, which in turn can influence plant growth and survival. Accordingly, there is growing con-cern that the spread of exotic earthworms into northern temperate forests may compromise biodiversityand tree species recruitment. We report on a study where we sampled earthworms, soils, and understoryplants in plots established in 40 mature sugar maple stands distributed over 3 areas in the EasternTownships of Southern Québec (Canada). Earthworms were found in 19 of 40 plots, and earthworm fre-quency of occurrence (Efo) as well as the complexity of earthworm communities reflected human acces-sibility to the plots. Plant species richness decreased, and species evenness increased, withEfo. TheEfowasrelated to a decrease in the cover of 5 plant species, and to an increase in the cover of 2 other plant speciesor plant functional groups. IncreasingEfoalso correlated with higher soil pH, lower forest floor thicknessand lower soil C:N ratio. Among these 3 variables, redundancy analysis (RDA) revealed that soil pH andforest floor thickness correlated with plant community composition. Based on neutral lipid and phospho-lipid fatty acid profiles, we found that soil bacteria and fungi increased with a decrease in forest floorthickness, bacteria and arbuscular mycorrhizal fungi (AMF) increased with soil pH, whereas actinobacte-ria and AMF increased withEfo. We discuss the possible mechanisms by which earthworms might directlyor indirectly alter understory plant community composition. By considering the location and land usemanagement of each study site, our study provides further evidence that the spread of exotic earthwormsin sugar maple stands of Southern Québec may be linked to human activities, with implications for fur-ther research and conservation issues.