Supervised by:

Vincent Maire (Regular member)

Co-supervised by:

Steeve Pépin (External collaborator)

Research project description

What is the relative importance of three limitations of photosynthesis on its variation in three willow species in an arctic glacial valley?

IntroductionHow vascular plants are able to achieve a positive carbon balance in extreme Arctic conditions is key to understanding their ability to colonize and thrive in those environments (Kumarathunge et al., 2019; Fernandez-Marin et al., 2020), as well as to anticipate the response of the tundra vegetation to global change which is twice to fourth times faster compared with other parts of the planet (Rantanen et al., 2022). Our current understanding of leaf photosynthesis that has largely been formulated using arid, tropical and temperate ecosystems, contrasts fast-growing species with slow-growing species which are characterized by more durable leaf tissue but with low photosynthetic capacity along the leaf economic spectrum (Wright et al 2004; Diaz et al 2016; Thomas et al. 2020). Yet, this is still relatively unclear how these variations in leaf chemical and morphological traits constrains the biochemical and biophysical limitations of the photosynthetic capacity in Arctic tundra. ObjectivesIn the present study, we focused on three willow species (S. arctica, S. richardsonii and S. reticulata) that widely occurred in the Qarlikturvik glacial valley on Bylot Island in Nunavut, Canada, and assess their photosynthetic capacity and limitations. For these species established in the High Arctic, we following objectives: (i) Determine if arctic willow species are particularly characterized by high LMA and PNUE values and low Narea, Parea and photosynthetic capacity Asat values as it would be expected from the leaf economic spectrum and arctic tundra stressful environment. (ii) Determine if Asat is more determined by components of the leaf nutrient-use efficiency (gs, gm, Vcmax at a given Narea) as observed in cold environments, rather than by investment of leaf nutrient concentration into Rubisco activity. (iii) Determine how Asat is determined by both proximal limitations (gs, gm, Vcmax) and distal nutrient economic traits (Narea, Parea and LMA), and their interactions.Study sitesThe study was conducted in the Qarlikturvik glacial valley of Bylot Island, Nunavut, Canada (73°09’N, 79°57’W). The average environmental conditions are as follows: altitude, 20 to 400 m; annual temperature, -14,4°C; snow, ~ 8 months year-1; permanent permafrost; precipitation 77.5 mm during the growing season (Domine et al., 2021). The Qarlikturvik Valley is located in the southwestern plain of the island and is crossed at its center by a glacier river. The valley is about 18 km long and has a terrace about 5 km wide at the bottom and is bordered by plateaus up to 500 m in altitude (Godin & Fortier 2012). The valley is rich in water bodies (proglacial river, lakes, ponds and polygons, small streams and thermo-erosion gullies) representing a typical glacial valley geosystem with numerous depositional environments, which includes alluvial, eolian, glaciofluvial, morainic, colluvial and marine sediments (Coulombes et al. 2021). Material and methodsWe selected 29 sites in 2019 to represent the diversity of ecosystems encountered in the Qarlikturvik valley, near the glacier to the ocean and from the wetlands along the river glacier up to the mesic plateau. Across sites, topsoils varied from 4.6 to 7.8 in pH, thawing depth varied from 20.5 to 71.5 cm, while site microclimate were less variable, from 5.8°C to 6.9°C in mean temperature and 0.141 to 0.203 kPa in VPD over the June-July-August growing period. At each site, we sampled the three Salix species, S. arctica, S. reticulata, S. richardsonii, whenever possible (24 of 29 sites presented the three species). For each sampling, three individuals of each species were cut and entirely covered with opaque material to encourage stomatal closure and limit water loss by transpiration during transport to the main camp. The individuals were left in the dark for 24 hours before being measured with the LiCOR Li6400XT and Li-6800 devices. Expected resultsWe expect that Asat increased both with leaf nitrogen concentration Narea and photosynthetic nitrogen use efficiency (PNUE) but at different rates across the three species, whereas it was not related with leaf phosphorus concentration Parea and photosynthetic phosphorus use efficiency PPUE when controlling for Narea and PNUE. Photosynthesis of three Salix species was mainly limited by biochemical processes of photosynthesis, despite high nitrogen concentration in leaf tissue. The latter were used to both increase Vcmax and gm. As such, our study would reveal evolutionary adaptation of photosynthesis to the habitat of Salix species. The erect shrub Salix richardsonii occurring in wet-habitat was more sensitive to stomatal conductance variation, whereas S. arctica and S. reticulata occurring in mesic-habitat were more sensitive to Rubisco, the photosynthesis enzyme, and it speed Vcmax. Our study provided valuable data for shrub species, responsible for the greening of the Arctic.

Research Site Coordinates

Scientific Communications

Lamarque, L., Jim, F.-F., Deschamps, L., Lévesque, E., Cusson, P.-O., Fortier, D., Giacomazzo, M., Guillemette, F., Paillassa, J., Tremblay, M., Maire, V., 2023. Hydrological Regime and Plant Functional Traits Jointly Mediate the Influence of Salix spp. on Soil Organic Carbon Stocks in a High Arctic Tundra. Ecosystems. DOI: 10.1007/s10021-023-00829-1.