thesis: WHAT ROLE DOES THE MICROCLIMATE PLAYS ON THE SENSITIVITY OF LEAF PHENOLOGY TO WARMING AND CONSEQUENCES ON FOREST RESILIENCE?
33140 VILLENAVE-D'ORNON
INRAE presentation
The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.
Work environment, missions and activities
-You will be welcomed in the unit Interactions Sol Plante ATmosphère (UMR 1391 ISPA) for PhD position
Project description:
Leaf phenology, the study of the drivers and dynamics of leaf budburst, unfolding, maturation and senescence, controls carbon, water and energy exchanges between forests and the atmosphere. Current approaches establish an empirical link between leaf phenology and standardised air temperature (the macroclimate), and fail to capture the true conditions sensed by trees (the microclimate). This results in a biased interpretation of the role of other factors, such as light, as well as the response of trees to climate warming, and leads to major uncertainties in the projections of forest dynamics and resilience.
The aim of this thesis project is to fill this gap by quantifying the role of microclimate on leaf phenology. By combining in situ observations, controlled experiments and modelling, this project will 1) quantify the microclimatic control of leaf phenology and clearly disentangle the factors that govern it, 2) develop new phenology models based on bud and leaf temperature and 3) reassess the sensitivity of phenology to past and future climate across scales.
Context:
The phenology of leaves, i.e. their development, growth and senescence, has a direct influence on forest productivity and biomass. It also influences local weather conditions and long-term climate through transpiration, albedo and carbon storage (Peñuelas et al. 2009). The rapidity of current climate change is leading to major disruptions in phenological cycles on a global scale, increasing the risks (e.g. of frost or spring drought) faced by trees that were adapted to past environmental conditions (Peaucelle et al. 2019). Despite centuries of research and observations, a thorough fundamental understanding of the environmental factors governing leaf phenology is still lacking. The poor representation of phenology in models of the terrestrial biosphere is considered to be one of the main uncertainties in carbon cycle estimates and future climate predictions.
Temperature is recognised as the main driver of leaf phenology in extra-tropical ecosystems. For this reason, phenology models generally rely on metrics based on the air temperature preceding phenological events, often in the form of a sum of degree-days. Numerous variants of phenological models have been proposed to describe budburst, growth and leaf senescence, including the duration of sunshine or photoperiod as another climatic variable, but with often limited success compared with a model based solely on growing degree-days. One of the reasons for these limitations is that today's climate is changing too quickly, so that models based on past and relatively 'stable' climatic conditions are not very good at predicting phenology in recent years, which have seen a number of record-breaking climatic extremes. Another reason is that these models are based on the average air temperature of a geographical location, also known as the 'macro-climatic' temperature, which does not allow us to capture the spatio-temporal variability in the landscape of organ temperatures (buds, leaves), and therefore phenology.
This thesis aims to study in greater detail the biophysical processes, and in particular the thermal processes, that control leaf phenology. Recent studies have highlighted the key role of solar radiation and biophysical properties such as bud and leaf albedo in spring phenology (Vitasse et al., 2021; Peaucelle et al. 2022) as well as in physiological activity, the latter being identified as a potential driver of leaf senescence. This suggests that the temperature conditions perceived by tree buds and leaves (i.e. the microclimate) are of key importance for understanding and accurately simulating leaf phenology and their response to future environmental conditions.
Objectives:
The general aim of this thesis project is to study the role of microclimate on leaf phenology in forests. More specifically, you will focus on European deciduous forest species for which microclimatic processes due to seasonal canopy closure are particularly pronounced (De Frenne et al. 2021), and you will seek to test the following two hypotheses:
(H1) The energy balance of buds or leaves is essential for disentangling the effects of temperature, radiation and photoperiod on leaf phenology.
(H2) Photoperiod-sensitive deciduous species perceive light through the photosynthetic tissues of the buds or bark.
Method:
To meet these objectives, you will be required to develop a multidisciplinary approach combining experiments under controlled conditions, field observations, data analysis and process modelling through 3 tasks:
1) Analyse the relationships between organ temperature (buds, leaves), phenology and environmental conditions. For this task, you will be required to carry out several controlled experiments (e.g. temperature, sunshine, irrigation, fertilisation) and to install sensors (e.g. thermal cameras) and take measurements (e.g. functional traits, photosynthesis) in the field.
2) Develop and calibrate a phenological model that considers bud and leaf temperature and the effect of microclimate. This task will involve evaluating existing models and developing a new phenology model based on the results of task 1.
3) Reassess the sensitivity of past and future leaf phenology to climatic conditions. The aim of this task will be to re-analyse past phenology data and make future predictions on several spatial and temporal scales using the phenology model developed in task 2. This new model could be coupled with other processes in order to quantify the role of phenology on the associated biogeochemical cycles in the context of global change.
References:
De Frenne P, Lenoir J, Luoto M, et al (2021) Forest microclimates and climate change: Importance, drivers and future research agenda. Global Change Biology 27:2279–2297. https://doi.org/10.1111/gcb.15569.
Peaucelle M, Peñuelas J, Verbeeck H (2022) Accurate phenology analyses require bud traits and energy budgets. Nature Plants 8:915– 922. https://doi.org/10.1038/s41477-022-01209-8.
Peaucelle M, Janssens IA, Stocker BD, Descals Ferrando A, Fu YH, Molowny-Horas R, Ciais P, Peñuelas J (2019) Spatial variance of spring phenology in temperate deciduous forests is constrained by background climatic conditions. Nature communications, 10, 5388.
Peñuelas J, Rutishauser T, Filella I (2009) Ecology. Phenology feedbacks on climate change. Science (New York, N.Y.), 324, 887–888.
Vitasse Y, Baumgarten F, Zohner CM, et al (2021) Impact of microclimatic conditions and resource availability on spring and autumn phenology of temperate tree seedlings. New Phytologist 232:537–550. https://doi.org/10.1111/nph.17606.
Training and skills
Master's degree/Engineering degree
-Recommended training: Master 2 or equivalent in environmental sciences.
-Knowledge required: Computer programming (R, Python), environmental data analysis.
- Appreciated experience: Theoretical or experimental research.
-Skills sought: Ability to work in a team, to write (scientific articles) and to express oneself (scientific conferences) in English. Keen interest in forest fieldwork, experimentation and modeling.
INRAE's life quality
By joining our teams, you benefit from (depending on the type of contract and its duration):
- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.
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