Matthias Cuntz (@mcuntz.bsky.social)

Measuring photosynthesis and respiration in high time-resolution with eddy covariance and wavelet analysis Land vegetation is currently under unprecedented pressure due to climate change. A better understanding of how plants respond to environmental stresses, such as heat waves and droughts, is essential for designing effective mitigation strategies.The eddy covariance method is now the leading method for measuring greenhouse gas exchanges between ecosystems and the atmosphere. It provides continuous, direct data that is widely used for studies on droughts, atmospheric inversions, satellite validation, etc. The method makes it possible to estimate the carbon sink of soils and plants, resulting from the balance between carbon absorbed by photosynthesis (gross primary productivity, GPP) and carbon emitted by ecosystem respiration (RE).The future of terrestrial carbon sinks will depend on the evolution of these carbon fluxes. Understanding how photosynthesis and respiration respond to extreme events (heat, drought) is therefore essential to guide the transition to a low-carbon economy and help ecosystems adapt.We have recently developed a method based on wavelet analysis to estimate ecosystem fluxes even under non-stationary conditions (Destouet et al. 2024). In addition, another study used wavelet analysis to estimate photosynthesis and respiration from the eddy covariance raw data (Coimbra et al. 2023).Objective: The aim of this thesis is to combine and improve these approaches in order to offer a comprehensive alternative to conventional data processing, including the partitioning of CO2 fluxes into photosynthesis and respiration. The method will be tested on data from the European research infrastructure ICOS (www.icos-cp.eu), which brings together more than one hundred sites equipped with instruments for monitoring carbon fluxes in ecosystems and covering a wide variety of ecosystems and climatic conditions. This thesis will contribute to a better understanding of how agricultural and forest ecosystems function by providing more reliable observations of the impact of climate on soils and plants. These results will be useful for research on water resources, extreme events, climate modelling and long-term monitoring of greenhouse gas emissions by terrestrial and ocean ecosystems, and by cities.Detailed information: https://www.macu.de/extra/PhD_Wavelet_long_en.pdf https://jobs.inrae.fr/en/ot-26342