|Tuesday, July 06|
Investigating the relationship between tree ecophysiology and hosted communities of epiphytic bryophytes and lichens
* Natalie Vuong, University of Waterloo, Canada
Fabio Gennaretti, Université du Québec en Abitibi-Témiscamingue
Julie Messier, University of Waterloo
Nicole Fenton, Université du Québec en Abitibi-Témiscamingue
Epiphytic bryophytes and lichens are abundant on a variety of tree species in different biomes. Trees within a single forest stand can exhibit contrasting states of health as a function of their physiological performance that may influence the epiphytic community. For example, a healthy tree may have a well-formed full crown structure while unhealthy tree crowns may be more eroded. Consequently, different physiological states of trees may support different communities. At a larger scale, this variation in tree health and subsequent variation in hosted communities may contribute to biodiversity and ecological processes, such as nutrient accumulation and carbon cycling, in unique ways . However, to date these links remain speculative. This study seeks to disentangle the relationship between tree ecophysiology and epiphytic communities at the local level. The ecophysiology of 20 black spruce (Picea mariana) from a northern Quebec boreal forest was characterized through measurements of age, diameter at breast height, basal area increment, stem water potential, maximum photosynthetic capacity , foliage density, and live crown ratio. Each tree was surveyed at the branch and trunk level for epiphytic species richness and coverage. Principal component analysis and linear regressions revealed that older, larger trees possessed poorer foliage and decreased in epiphyte coverage at the trunk level, likely due to the development of unsuitable habitat conditions along the trunk with age . Preliminary results suggest opposite trends at the branch level. The links between tree physiology and epiphyte community composition and abundance could lead to predictive landscape level models for conservation planning.
Arboreal Gastropod Grazing in Macro-Lichen Communities of Western Newfoundland
* Katherine Flores, Memorial University/Canadian Forest Service, Canada
André Arsenault, Canadian Forest Service
Michele Piercey-Normore, Memorial University of Newfoundland
Gastropod grazing has recently emerged as a potential threat to the continued existence of some species of epiphytic macro-lichens in eastern North America. The island of Newfoundland represents a strong hold for many species of rare or endangered lichen species. This study examines how gastropod species currently alter lichen communities in western Newfoundland by investigating three questions: (1) Has lichen grazing by arboreal gastropods occurred in western Newfoundland? (2) What is the abundance and richness of arboreal gastropods present in the study area? (3) Does damage by grazing to lichen thalli vary in relation to tree level environmental factors (e.g., lichen diversity, DBH)? We used field lichen grazing surveys and lichen abundance and diversity surveys to describe the current state of the lichens in the study area. We used nocturnal timed gastropod searches and arboreal pit-fall traps to describe the abundance and richness of arboreal gastropods. Preliminary results show 68% of lichen thalli had severe or extreme grazing. Gastropod sampling methods collected 275 gastropod specimens including 234 slugs and 41 snails. Regardless of sampling method, slugs outnumbered snails in the observed arboreal gastropod community. Grazing damage was significantly higher for trees with lower lichen species diversity and those where lichens were found on the tree bole. Lobaria pulmonaria (L.) Hoffm. was the most severely grazed of all lichen species surveyed. Overall, lichen communities in western Newfoundland were severely impacted by widespread gastropod grazing, but further research is required to understand the relationship of lichen species diversity and grazing severity.
Calicioid fungi and lichens from an unprotected intact forest ecosystem in Québec
* Philip Bell-Doyon, Université Laval, Canada
Steven B. Selva, University of Maine at Fort Kent
R. Troy McMullim, Canadian Museum of Nature
Calicioid lichens and fungi form a diverse polyphyletic group whose species richness is often associated with old-growth forests and ecological continuity. One of the last intact forest landscapes south of the 50th parallel in Québec includes the Ya’nienhonhndeh territory, which has been the focus of a protected area project directed by the Huron-Wendat First Nation for more than ten years. To contribute to the characterization of its conservation value, we report the calicioids from the area. We identified 34 species in eight genera from 187 samples collected in old growth stands of balsam fir, black spruce, and yellow birch. Our four most remarkable discoveries are Chaenotheca nitidula Tibell (n = 11), Chaenothecopsis australis Tibell (n = 1), and C. tsugae Rikkinen (n = 2), which are reported for the first time from the province, as well as Sclerophora coniophaea (Norman) Mattsson & Middelb. (n = 18), which is rare in North America and was previously reported only once in Québec. As a result of this inventory, the Ya’nienhonhndeh is now the second richest area known for calicioids in Québec, after Parc national de la Gaspésie. We conclude that it is an ancient forest ecosystem whose conservation value is high based on its unique biodiversity, and that it warrants protection.
Microbial community associated to lichens in a post-fire succession
* Marta Alonso-Garcia, Université Laval, Canada
Juan Carlos Villarreal Aguilar, Université Laval
Lichens are symbiotic organisms between fungi (one-several species), green algae and/or cyanobacteria and numerous bacteria. While the interactions between the photobiont and fungus have been intensively studied, the characterization of microorganisms and its role in the symbiosis is still in its infancy. In this project we aim to assess the abundance and diversity of the whole microbial community associated to two reindeer lichen species, Cladonia mitis and C. stellaris, and to compare the changes of those microorganisms in a post-fire succession. To achieve these goals, DNA and RNA from lichen samples were extracted. We carried out library preparation and sequencing on an Illumina MiSeq platform. We binned the assembled contigs to group and assign them to individual genomes, such as fungi, algae, bacteria, or viruses. Microbial composition analyses were performed using both, R and MetaVir2 softwares. Our preliminary results show that ca. 190 potential RNA viruses are found in both lichen species, whereas the number of potential DNA viruses varied between them. Around 300 potential DNA viruses are associated to C. mitis, by contrast less than 10 are found in C. stellaris. The abundance of bacteria associated to reindeer lichens follows the opposite pattern. Samples of C. stellaris harbor 10 times more bacteria taxa than C. mitis. Regarding the microbial composition along a post-fire succession, we expected to find that, in the first stages of the postfire succession, abundance and diversity of microorganisms will increase but, decrease over time once the environmental conditions are stable.
Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation
* Jean-Philippe Bellenger, Universite de Sherbrooke, Canada
Romain Darnajoux, Princeton Univeristy
Nicolas Magain, Duke University
Marie Renaudin, Universite de Sherbrooke
Francois Lutzoni, Duke University
Xinning Zhang, Princeton university
Biological Nitrogen Fixation (BNF) is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the molybdenum nitrogenase and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking. Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect and at the end of the growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.glichen-1 for the onset of vanadium based BNF. This study provides evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.
Toward the transportome of the lichen Peltigera britannica
* Tami McDonald, St. Catherine University, United States
Background: Unlike most other members of the predominantly cyanobacterial lichen genus Peltigera, the lichen Peltigera britannica is tripartite, having a green alga (Coccomyxa sp.) as its primary photobiont and a cyanobacterium (Nostoc sp.) as a secondary photobiont housed in specialized structures called cephalodia in which atmospheric nitrogen is fixed. In tripartite lichen associations, nutrient exchange occurs both between the alga and the fungus and between the cyanobacterial partner and the fungus at separate interfaces. Accomplishing these nutrient exchanges requires an efflux step and an import step across the symbiotic interface, each needing a different transporter. Objective: To define the “transportome” of a tripartite lichen by identifying in P. britannica thalli the transporters hypothesized to mediate the flux of carbon and nitrogen between symbionts. Methods: Genome and transcriptome data were employed to identify in P. britannica thalli the transporters mediating the exchange of sugar and sugar alcohols, ammonium, nitrate, amino acids, and other substrates. A subset of these transporters was cloned and expressed in heterologous systems, including yeast and Xenopus oocytes, for characterization. Results: Multiple members of each transporter type were identified in the genomes of each of the symbionts. Two putative polyol transporters were identified in the genome of the lichenizing fungus. When expressed in Xenopus oocytes, neither was functional, necessitating additional assays. Conclusions: Both yeast and Xenopus oocytes can be useful for heterologous expression of genes from lichen symbionts. Additional yeast mutants engineered to metabolize specialized substrates such as polyols are required.