Where: BIOGECO INRAE – University of Bordeaux
When: Starting date – early 2025 (6 Months).
Application deadline: 31th November 2024
Supervisors: Marta Benito Garzón, Marion Carme and Eduardo Vicente (BIOGECO – E4E)
Contact person: marta.benito-garzon@inrae.fr
Funding: H2020 SUPERB
Integration in other projects: Horizon Europe OPTFOREST
Submitted related projects: ECOS Nord-Mexique Climate driven germination adaptations in conifer tree species of Mesoamerica’s mountains
Required skills: M1 in ecology, excellent modeling skills, good knowledge of R environment, team work capacity.
STATE OF THE ART
Climate change is disrupting biological cycles, altering ecosystems and changing forests communities at an unprecedented pace. Tree populations can survive under climate change by moving towards more favorable conditions (Chen et al., 2011; Sunday et al., 2011), or persisting in-situ by evolutionary processes, including genetic adaptation and phenotypic plasticity (Valladares et al., 2014). These processes can be quantified from common gardens, where trees from different origins are planted all across the species ranges (Leites & Benito Garzón, 2023). However, current knowledge on tree populations’ responses to climate change at large geographical scales is mostly based on adult trees, even though early developmental stages are far more sensitive to climate than adult ones and tightly linked to fitness (Verdú & Traveset, 2005). Therefore, new knowledge on the sensitivity to climate of the early phases of trees is urgently needed to assure forests persistence.
The first processes of early-life tree stages encompass germination, including dormancy breaking (for orthodox seeds, i.e. those seeds tolerating desiccation to moisture contents below 5%), as well as growth, survival and phenology after germination. Most temperate trees present orthodox seeds allowing them to persist in bank soils and to be stored for long periods. Among them, many present physiological dormancy, i.e. their germination is prevented by endogenous physiological processes (e.g. hormonal or metabolic). The mechanisms involved in breaking physiological dormancy are controlled by specific environmental cues (e.g. temperature, moisture.) (Baskin & Baskin, 2001; Finch-Savage & Leubner-Metzger, 2006), therefore, germination in species with this dormancy type is very sensitive to any environmental change. Furthermore, the duration and intensity of environmental requirements to break physiological dormancy can vary greatly between species. Accordingly, species are classified along a spectrum of non-deep – intermediate – deep dormancy.
Physiological dormancy is an adaptive mechanism that protect seedlings from frost damage during harsh conditions, and hence it has been widely developed in trees inhabiting cold and temperate regions with harsh winters (Rosbakh et al., 2023). Particularly, many of these species require a period of cold (around 3-5ºC) and moist conditions to induce dormancy breaking, which is normally meet at spring onset or when snow melts. As adaptive trait, physiological dormancy can change among mother trees, populations and species (Andersson & Milberg, 1998; Kaye et al., 2018; Monemizadeh et al., 2021). Maladaptation to new climatic conditions can be expected in some cases, provoking lack of germination if cold conditions are not fulfilled.
Our knowledge on how environmental alterations affect dormancy and germination is very limited (Vicente Bartoli & Benito Garzón, 2024), including how this may impact seedlings early-stage fitness. Indeed, germination and its phenology can have cascading effects on the development and survival of seedlings, as well as on the functional traits that modulate their fitness (Donohue et al., 2010; Gremer et al., 2020). For instance, the seed reservoir is mostly used by the cotyledons and hence bigger seeds tend to show faster shoot elongation and first leaf emergence. This can influence the overall seedling growth and the development of leaf and root morphologies controlling resources’ acquisition and use (Donohue et al., 2010). Likewise, leaf protective pigments as flavonols and anthocyanins can confer protection to stressful environmental conditions as drought and cold temperatures (Chalker-Scott, 1999), in detrimental of other leaf pigments as chlorophyll. Thus, they can be of great importance for early seedlings’ survival. In addition, fitness related traits often show consistent co-variations across species ranges, indicating that seedlings’ fitness can be modulated by the integrated response of different traits (Laughlin et al., 2020).
The main goal of this M2 internship is to understand the relationship between dormancy release and fitness of early phenotypes for five species representing the extremes in the physiological dormancy gradient in Europe: European beech (Fagus sylvatica L.; Abies alba Mill, Pinus nigra R. Legay non-deep physiological dormancy), European maple (Acer pseudoplatanus L.; intermediate physiological dormancy) and wild cherry (Prunus avium L.; deep physiological dormancy). The expected results will bring us light on the adaptive and environmental adjustments of early stages traits along the dormancy tree spectrum to warming temperature, informing assisted gene flow programs and contributing to understand forest regeneration in a warming world.
HYPOTHESIS/OBJECTIVES
Understanding the relationship between the dormancy breaking needs, germination and post-germination traits is essential to predict forest regeneration and management. We expect that warmer populations can germinate after shorter stratification (or without) than colder populations (i.e. they have adapted to warmer winters and hence are able to germinate under such circumstances). Furthermore, seeds following stratification may produce more vigorous seeds and require shorter times to germinate than stratified seeds, increasing hence the overall fitness of the seedlings (Postma & Ågren, 2022). The internship objective is explore the relationship between the degree of dormancy (stratified or non-stratified seeds) and fitness (traits measured just after germination) at the inter- and intra-specific levels.
METHODS
1/ Seed collection. Seed collection from range-wide populations is performed in the framework of the EU- funded project OPTFORESTS. All seeds from at least 2 populations per species have been already collected and stored at -5°C at BIOGECO. The only exception is Fagus sylvatica, which seeds will be collected in the autumn of 2024. If this is not a masting year, this species will be eliminated from the experiment, which will be still assured by the other 4 species.
2/ Lab work. Laboratory work includes dormancy breaking experiments, germination monitoring and postgermination traits measurements under controlled conditions. We will break the seed dormancy at humid and cold conditions for 3 to 4 weeks to simulate winter cold. Afterwards, we will germinate the seeds in growing chambers in nursery trays in climatic chambers located at INRAE BIOGECO-University of Bordeaux (Snijder LABS, micro clima-series) set at temperatures of 20 °C, maintaining a constant 75% relative humidity, light intensity at 100 µmol m−2 s−1, and a photoperiod of 14/10 light/dark hours, emulating the conditions required for germination during springtime. The student will monitor germination three days per week during 1 month, first leaf emergence, and height. These laboratory work has been already performed by the team for Abies alba and Acer pseudoplatanus in 2024, and the database is ready to be analysed, which assures the internship in case of germination failure encountered by the other species.
3/ Statistical analysis and modeling. We will calibrate Cox’s hazard models of germination dynamics for each species using the daily germination data under different stratification scenarios (dormancy breaking). To analyze the early phenotypes we will use phenotypic integration techniques as structural equation models (Benito Garzón, 2021; Santini et al., 2019) and trait correlation networks (Benavides et al., 2021).
REFERENCES
Andersson, L., & Milberg, P. (1998). Variation in seed dormancy among mother plants, populations and years of seed collection. Seed Science Research, 8(1), 29–38. https://doi.org/10.1017/S0960258500003883
Baskin, C. C., & Baskin, J. M. (2001). SEEDS Ecology, biogeograpghy, and evolution of dormancy and germination. Academic Press.
Benavides, R., Carvalho, B., Matesanz, S., Bastias, C. C., Cavers, S., Escudero, A., Fonti, P., Martínez-Sancho, E., & Valladares, F. (2021). Phenotypes of Pinus sylvestris are more coordinated under local harsher conditions across Europe. Journal of Ecology, 109(7), 2580–2596. https://doi.org/10.1111/1365-2745.13668
Benito Garzón, M. (2021). Phenotypic integration approaches predict a decrease of reproduction rates of Caribbean pine populations in dry tropical areas. Annals of Forest Science, 78, 1–19. https://doi.org/DOI: 10.1007/s13595-021-01076-x
Chalker-Scott, L. (1999). Environmental Significance of Anthocyanins in Plant Stress Responses. Photochemistry and Photobiology, 70(1), 1–9. https://doi.org/10.1111/j.1751-1097.1999.tb01944.x
Chen, I. C., Hill, J. K., Ohlemüller, R., Roy, D. B., & Thomas, C. D. (2011). Rapid range shifts of species associated with high levels of climate warming. Science (New York, N.Y.), 333(6045), 1024–1026. https://doi.org/10.1126/science.1206432
Donohue, K., Rubio de Casas, R., Burghardt, L., Kovach, K., & Willis, C. G. (2010). Germination, Postgermination Adaptation, and Species Ecological Ranges. Annual Review of Ecology, Evolution, and Systematics, 41(1), 293–319. https://doi.org/10.1146/annurev-ecolsys-102209-144715
Finch-Savage, W. E., & Leubner-Metzger, G. (2006). Seed dormancy and the control of germination. New Phytologist, 171(3), 501–523. https://doi.org/10.1111/j.1469-8137.2006.01787.x
Gremer, J. R., Chiono, A., Suglia, E., Bontrager, M., Okafor, L., & Schmitt, J. (2020). Variation in the seasonal germination niche across an elevational gradient: The role of germination cueing in current and future climates. American Journal of Botany, 107(2), 350–363. https://doi.org/10.1002/ajb2.1425
Kaye, T. N., Sandlin, I. J., & Bahm, M. A. (2018). Seed dormancy and germination vary within and among species of milkweeds. AoB PLANTS, 10(2), ply018. https://doi.org/10.1093/aobpla/ply018
Laughlin, D. C., Gremer, J. R., Adler, P. B., Mitchell, R. M., & Moore, M. M. (2020). The Net Effect of Functional Traits on Fitness. Trends in Ecology & Evolution, 35(11), 1037–1047. https://doi.org/10.1016/j.tree.2020.07.010
Leites, L., & Benito Garzón, M. (2023). Forest tree species adaptation to climate across biomes: Building on the legacy of ecological genetics to anticipate responses to climate change. Global Change Biology, 29(17), 4711–4730. https://doi.org/10.1111/gcb.16711
Monemizadeh, Z., Ghaderi-Far, F., Sadeghipour, H. R., Siahmarguee, A., Soltani, E., Torabi, B., & Baskin, C. C. (2021). Variation in seed dormancy and germination among populations of Silybum marianum (Asteraceae). Plant Species Biology, 36(3), 412–424. https://doi.org/10.1111/1442-1984.12326
Postma, F. M., & Ågren, J. (2022). Effects of primary seed dormancy on lifetime fitness of Arabidopsis thaliana in the field. Annals of Botany, 129(7), 795–808. https://doi.org/10.1093/aob/mcac010
Rosbakh, S., Carta, A., Fernández-Pascual, E., Phartyal, S. S., Dayrell, R. L. C., Mattana, E., Saatkamp, A., Vandelook, F., Baskin, J., & Baskin, C. (2023). Global seed dormancy patterns are driven by macroclimate but not fire regime. New Phytologist, 240(2), 555–564. https://doi.org/10.1111/nph.19173
Santini, F., Climent, J. M., & Voltas, J. (2019). Phenotypic integration and life history strategies among populations of Pinus halepensis: An insight through structural equation modelling. Annals of Botany, 124(7), 1161–1171. https://doi.org/10.1093/aob/mcz088
Sunday, J. M., Bates, A., & Dulvy, NK. (2011). Global analysis of thermal tolerance and latitude in ectotherms. Proceedings of the Royal Society B: Biological Sciences, 278(1713), 1823–1830. https://doi.org/10.1098/rspb.2010.1295
Valladares, F., Matesanz, S., Guilhaumon, F., Araújo, M. B., Balaguer, L., Benito-Garzón, M., Cornwell, W., Gianoli, E., van Kleunen, M., Naya, D. E., Nicotra, A. B., Poorter, H., & Zavala, M. A. (2014). The effects of phenotypic plasticity and local adaptation on forecasts of species range shifts under climate change. Ecology Letters, 17(11), 1351–1364. https://doi.org/10.1111/ele.12348
Verdú, M., & Traveset, A. (2005). Early Emergence Enhances Plant Fitness: A Phylogenetically Controlled Meta-Analysis. Ecology, 86(6), 1385–1394. https://doi.org/10.1890/04-1647
Vicente Bartoli, E., & Benito Garzón, M. (2024). Tree germination sensitivity to increasing temperature, a global meta-analysis across biomes, species and populations. Global Ecology and Biogeography. Accepted
Commentaires récents