Sarah-Sophie Weil is a PhD student at the Université Grenoble Alpes in France. She is a biogeographer interested in macroecological patterns at different time scales. Here, Sarah shares her recent work on how plant-soil interactions impact environmental changes in terrestrial ecosystems.
After climbing up many mountains in the French Alps during fieldwork, time for a change: Sarah, nearly on top of Mount Snowdon, Snowdonia National Park, Wales, UK.
Institute. Department of Biosciences, Swansea University, Wales, UK | Laboratoire d’Ecologie Alpine, Université Grenoble Alpes, Grenoble, France.
Academic life stage. PhD student.
Major research themes. Biogeography, macroecology, movement ecology and dispersal.
Fieldwork in the Chartreuse Mountains, showcasing one of the difficulties of this project: defining 30 x 30m plots on a very steep slope.
Current study system. In the context of my PhD, I am currently working on the role of traits in dispersal across different timescales (in biogeographic histories of clades, present-day invasions and under future climate change scenarios). My recently published paper in JBI developed from my Master’s dissertation in which I analysed the relationships between plant traits, e.g., height or leaf dry matter content, soil microbial activities and environmental conditions in the French Alps. Plant-soil relationships are intricate, and it is difficult to say who is influencing who or if it’s reciprocal. That’s why it was so fascinating (and challenging) to work on these relationships!
Recent JBI paper. Weil SS, Martinez-Almoyna C, Piton G, Renaud J, Boulangeat L, Foulquier A, Saillard A, Choler P, Poulenard J, ORCHAMP Consortium, Münkemüller T, Thuiller W (2021). Strong links between plant traits and microbial activities but different abiotic drivers in mountain grasslands. Journal of Biogeography, 48(11), 2755-2770 https://doi.org/10.1111/jbi.14235.
Fieldwork in the Mercantour (France), halfway up the mountain.
Motivation behind this paper. The plant and soil communities in an ecosystem are interdependent, with their interactions being fundamental elements of ecosystem functioning. However, we know relatively little about how plant-soil linkages vary in response to environmental conditions at large scales. Considering future environmental changes, we wanted to fill this knowledge gap. In addition, the soil microbial community is often assumed to be responding to the plant community. Still, the soil microbial community can also influence the plant community because it determines nutrient availability. That’s why we employed a novel method, called graphical lasso, to tease apart direct and indirect influences in plant-soil linkages without defining the direction of these influences beforehand. Altogether, we wanted to develop a comprehensive picture of plant-soil linkages and abiotic influences on a large scale that covers many climatic and edaphic conditions.
Fieldwork in the Mercantour (France), close to the top of Mont Mounier. How do you plant beacons with 30cm steel rods into the soil when there is barely any soil to work with?
Key methodologies. Our goal was to develop a network including variables related to plant-soil linkages (e.g., plant functional traits like plant height or leaf nitrogen content, soil enzymatic activities, which indicates nutrient availability) and abiotic conditions (e.g., temperature, pH, soil organic matter, etc.). To do so, we used a novel approach by employing graphical lasso, a model that can infer partial correlations between all included variables. Partial correlations are a way to identify connections between a pair of variables while controlling for possible confounding variables. This approach allowed us to identify direct and indirect relationships between plants, belowground microbial community, and abiotic soil and climatic variables without imposing a directional structure. To cover a large range of climatic and edaphic conditions, we used data from 41 plots situated between 1500 and 2800 m of elevation in the French Alps.
Unexpected challenges. There were numerous challenges during fieldwork. Hiking up mountains with heavy equipment to install the plots, finding the plots later on to perform measurements, the species identification work performed by botanists, and the lab work done for the enzymatic activities was a huge undertaking collectively performed by all the authors involved and many interns. Because I was not present for most of the fieldwork, a personal challenge for me was to dive into the research of plant-soil linkages. It is an interdisciplinary research area, and it requires knowledge about all components. Not only did I learn many things about plant communities, but I also had to integrate knowledge about the soil microbial community. On top of that, of course, were the abiotic influences – how do plant and soil microbial communities vary with temperature? Which influence do precipitation and solar radiation have? And an additional challenge was that this work was carried out under time pressure, having only four months to produce the results for my Master’s thesis.
Botanical rélevés in Chamechaude (France): identifying all plants (presence/absence) in a 3m-wide transect across the plot (photo credit: Wilfried Thuiller).
Major results. We found that abiotic drivers are key elements in plant-soil linkages in the French Alps. Plant traits were strongly linked to climate, and soil enzymatic activities (indicating investment in soil microbial nutrient acquisition) were associated with soil properties. Climate only influenced the biotic and abiotic soil compartments through cascading effects via plant traits linked to the soil carbon/nitrogen ratio. This relationship highlights the role of plant-soil interactions in ecosystem responses to abiotic changes. In these plant–soil linkages, specific plant traits were more important than their diversity. In sites with conservative plant traits, such as high leaf mass per area and reduced organic matter quality, soil microbes invested more strongly in nutrient acquisition.
Next steps for this research. The data for this study comes from the long-term observation network ORCHAMP (https://orchamp.osug.fr/home), which consists of ca. 30 elevational gradients that have each 3-7 plots every 200m of altitude. The study featured here is just a small part of the effort to better understand biodiversity patterns and ecosystems functioning in mountain regions. On-going and future works focus on deciphering environmental predictors (e.g., climate, soil, human use, vegetation) of the multiple trophic groups occurring in the soil, understanding the spatial turnover of soil interaction networks, and producing predictive models of soil biodiversity in space and time.
Botanical rélevés in Anterne (France): the pin-point method. Along a transect in the middle of the plot, two measurements were taken every 20cm: one 25cm upslope, the other 25cm downslope from the transect. All individuals touching the poles per 20cm increment were identified and counted (photo credit: Carole Birck).
If you could study any organism on Earth, what would it be? I admit, I am more interested in general patterns and understanding the processes and mechanisms that drive them. That being said, I’ve always been fascinated by trees because some species can have such long lifespans. To think about what these trees must have experienced and survived – natural disasters like fires and storms, changes in climate, etc. – is just mind-boggling!