Honorine Dumontel

Microorganisms play a fundamental role in the global carbon (C) cycle, influencing whether terrestrial ecosystems act as sources or sinks of atmospheric CO₂. Their response to climate change, particularly to warming, is a crucial but poorly understood component of climate-C cycle feedbacks.

Hence, PhD research focuses on microbial feedback to climate change by using thermal traits to link microbes to biogeochemistry, supervised by Johannes Rousk and Lettice Hicks.

The central objective of my project is to assess the temperature dependences of microbial growth and respiration in three different biomes – subarctic tundra, temperate forest and tropical forests – to elucidate the type, magnitude and speed of microbial adaptation to climate change.

My ongoing projects examine the effect of warming on microbial growth and respiration thermal traits using (1) an in situ translocation experiment in a tropical elevation gradient (Costa Rica) and (2) field warming experiments (winter warming, summer warming, and heatwave simulation) in the Subarctic (Abisko) and temperate systems (Lund).

To assess microbial temperature dependences, we conduct laboratory incubations across a range of temperatures. For this, we use radioisotopes to measure microbial growth—including both bacteria and fungi—and gas chromatography to measure respiration. This allows us to quantify both carbon assimilation for biomass formation (growth) and carbon losses (respiration) to the atmosphere. Additionally, we can determine carbon-use efficiency (CUE), which helps us understand whether soils act as carbon sinks or sources under climate warming.