I am looking for an excellent Master1 or Master2 student to apply for a PhD thesis grant co-financed by Labex TULIP in Toulouse and my own research programs.
The student can come from anywhere in the world, it is just necessary that he applies to a call currently in progress (the deadline to answer is September 7) . The thesis can start between January 1, 2022 and December 2022.
It is compulsory that the candidate has excellent grades in bachelor and master programs because it is the major criterion of selection.
Here is an a preliminary description of the PhD Project:
Title: Belowground plant functional diversity as driver of ecosystem functioning stability in conditions of drought
Titre: Rôle de la diversité fonctionnelle racinaire des plantes dans la stabilité du fonctionnement des écosystèmes en conditions de sécheresse.
Supervisors: Grégoire Freschet
Key-words: Plant diversity; mycorrhiza; drought; plant production; soil functioning; ecosystem stability
This PhD project will explore the role of plant diversity, and particularly root functional traits and trait diversity, using functional ecology approaches, in order to shed light on the processes regulating Biodiversity – Ecosystem Functioning relationships in conditions of drought. The PhD candidate will test the hypothesis that both plant trait promoting drought resistance and the diversity of drought-resistance strategies among co-existing plants positively impact on ecosystem multifunctionality and the stability of these functions. The candidate will test such hypotheses in two systems: perennial herbaceous grasslands and vegetable gardening systems promoting plant associations. To do so, he/she will rely on experimentations whereby the diversity of herbaceous and vegetable plants, respectively, will be manipulated across contrasting conditions of drought. Plant functional trait diversity will be characterized, as well as their effect on the stability of multiple soil and soil microorganism properties and major ecosystem functions including farmers’ yield and soil carbon and nutrient status.
State of the art
A large body of works in ecology has shown that both the number of species and the diversity of functions carried out by species in an ecosystem are of primary importance for the regulation of ecosystem functioning and services (van der Heijden et al. 1998; Lange et al. 2015; Hazard & Johnson 2018). However, several recent syntheses (Johnson et al. 2012; Fernandez & Kennedy 2015; Rillig et al. 2015; Hazard & Johnson 2018) shed light on our limited knowledge of the mechanisms associated to root systems and their symbionts that underlie such biodiversity – ecosystem functioning relationships. These syntheses suggest nonetheless that the huge diversity of root traits could play a critical role in ecosystem functioning. Indeed, the positive effects of plant diversity generally observed on soil functions appear strongly dependent on characteristics of the root systems (Cong et al. 2014; Lange et al. 2015).
In parallel, it is well known that biodiversity – ecosystem functioning relationships can to a large extent be modulated by environmental variations (e.g. the type of soil, resource availability, environmental stress and disturbance, climate changes) (Isbell et al. 2011; De Laender et al. 2016). However, whether and how plant belowground strategies play a substantial role in these modulations remains largely untested (Isbell et al. 2015). This is despite a number of hypothesized effects of the diversity of plant on the stability of ecosystem functions (e.g.,Grossiord 2020).
Additionally, most knowledge on diversity – ecosystem functioning relationships come from the study of ecosystem productivity, and very few have looked at a range of functions (Hector & Bagchi 2007; Isbell et al. 2011; Maestre et al. 2012). Further, the relevance of focal ecosystem functions appears rather limited because only poorly integrative and representative of the whole range of services provided by ecosystems and agroecosystems (Swift, Izac & van Noordwijk 2004).
In this context, it appears particularly timely and relevant to initiate interdisciplinary projects bridging root ecology (e.g. related to root system functional diversity in terms of architecture, morphology, chemistry, physiology and symbiotic associations) (Freschet et al. 2018; Freschet et al. 2020; Freschet et al. 2021), plant responses to climatic stresses (Brunner et al. 2015; Volaire 2018) and ecosystem functioning (Fanin et al. 2017; Yuan et al. 2020). Such interdisciplinary research, by manipulating the diversity of plant functional strategies, can provide mechanistic evidence of their potential role in a large set of ecosystem functions. By manipulating soil water resources, such experiments will further test the potential importance of plant associations on the stability of ecosystem functions over time.
Original aspects of this project proposal are:
– a truly multidisciplinary approach integrating methods and knowledge from plant physiology, plant functional ecology, soil ecology and agronomy.
– a true replication of our approach in two contrasting agronomical systems.
– a focus on the interactions between environmental variation and biodiversity to gain further insight into the context-dependency of the effect of biodiversity on ecosystems.
– a coupling of fundamental science questions and agronomical applications.
– a holistic approach of ecosystem functioning with direct link to ecosystem services valued by managers as well as by conservationists.
Brunner, I., Herzog, C., Dawes, M.A., Arend, M. & Sperisen, C. (2015) How tree roots respond to drought. Frontiers in plant science, 6, 547.
Cong, W.-F., van Ruijven, J., Mommer, L., De Deyn, G.B., Berendse, F. & Hoffland, E. (2014) Plant species richness promotes soil carbon and nitrogen stocks in grasslands without legumes. Journal of Ecology, 102, 1163-1170.
De Laender, F., Rohr, J.R., Ashauer, R. et al. (2016) Reintroducing environmental change drivers in biodiversity–ecosystem functioning research. Trends in Ecology & Evolution, 31, 905-915.
Fanin, N., Gundale, M.J., Farrell, M., Ciobanu, M., Baldock, J.A., Nilsson, M.-C., Kardol, P. & Wardle, D.A. (2017) Consistent effects of biodiversity loss on multifunctionality across contrasting ecosystems. Nature Ecology & Evolution.
Fernandez, C.W. & Kennedy, P.G. (2015) Moving beyond the black-box: fungal traits, community structure, and carbon sequestration in forest soils. New Phytologist, 205, 1378-1380.
Freschet, G.T., Pagès, L., Iversen, C.M. et al. (2020) A starting guide to root ecology: strengthening ecological concepts and standardizing root classification, sampling, processing and trait measurements New Phytologist, in press.
Freschet, G.T., Roumet, C., Comas, L.H. et al. (2021) Root traits as drivers of plant and ecosystem functioning: current understanding, pitfalls and future research needs. New Phytologist, in press.
Freschet, G.T., Violle, C., Bourget, M.Y., Scherer-Lorenzen, M. & Fort, F. (2018) Allocation, morphology, physiology, architecture: the multiple facets of plant above and belowground responses to resource stress. New Phytologist, 219, 1338-1352.
Grossiord, C. (2020) Having the right neighbors: how tree species diversity modulates drought impacts on forests. New Phytologist, 228, 42-49.
Hazard, C. & Johnson, D. (2018) Does genotypic and species diversity of mycorrhizal plants and fungi affect ecosystem function? New Phytologist, 220, 1122-1128.
Hector, A. & Bagchi, R. (2007) Biodiversity and ecosystem multifunctionality. Nature, 448, 188.
Isbell, F., Calcagno, V., Hector, A. et al. (2011) High plant diversity is needed to maintain ecosystem services. Nature, 477, 199.
Isbell, F., Craven, D., Connolly, J. et al. (2015) Biodiversity increases the resistance of ecosystem productivity to climate extremes. Nature, 526, 574-577.
Johnson, D., Martin, F., Cairney, J.W.G. & Anderson, I.C. (2012) The importance of individuals: intraspecific diversity of mycorrhizal plants and fungi in ecosystems. New Phytologist, 194, 614-628.
Lange, M., Eisenhauer, N., Sierra, C.A. et al. (2015) Plant diversity increases soil microbial activity and soil carbon storage. Nature Communications, 6, 6707.
Maestre, F.T., Quero, J.L., Gotelli, N.J. et al. (2012) Plant species richness and ecosystem multifunctionality in global drylands. Science, 335, 214-218.
Rillig, M.C., Aguilar-Trigueros, C.A., Bergmann, J., Verbruggen, E., Veresoglou, S.D. & Lehmann, A. (2015) Plant root and mycorrhizal fungal traits for understanding soil aggregation. New Phytologist, 205, 1385-1388.
Swift, M.J., Izac, A.M.N. & van Noordwijk, M. (2004) Biodiversity and ecosystem services in agricultural landscapes—are we asking the right questions? Agriculture, Ecosystems & Environment, 104, 113-134.
van der Heijden, M.G.A., Klironomos, J.N., Ursic, M., Moutoglis, P., Streitwolf-Engel, R., Boller, T., Wiemken, A. & Sanders, I.R. (1998) Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity. Nature, 396, 69.
Volaire, F. (2018) A unified framework of plant adaptive strategies to drought: Crossing scales and disciplines. Global Change Biology, in press.
Yuan, Z., Ali, A., Ruiz-Benito, P. et al. (2020) Above- and below-ground biodiversity jointly regulate temperate forest multifunctionality along a local-scale environmental gradient. Journal of Ecology, 108, 2012-2024.