Here is a brief overview of my research activity on forest carbon and nitrogen cycling.
I am currently working at the Guyaflux tower experimental site in French Guiana, which is a station in international research networks such as ICOS, FLUXNET and FLUXNET-CH4. These European and American networks collect long-term continuous observations of energy and greenhouse gases, i.e. CO2, CH4, N2O and H2O vapour, exchanges between terrestrial ecosystems and the atmosphere using the eddy-covariance technique, and analyse their magnitudes and patterns across biomes.
I have also led studies in Wytham Wood (UK), the Barro Colorado Nature Monument (Panama) and the Victoria-Mayaro Reserve Forest (Trinidad).
I have also led studies in Wytham Wood (UK), the Barro Colorado Nature Monument (Panama) and the Victoria-Mayaro Reserve Forest (Trinidad).
①⑤⑥ Advancing knowledge in the understanding of the greenhouse gas sink or source potentials of a tropical rainforest
Paracou in French Guiana (blue dot)
In the RainForest-GHG project, an MSCA Individual Fellowship, we investigated the contributions of the main ecosystem compartments, i.e. soil, tree, atmosphere, to the fluxes of three critical climate-forcing trace gases, i.e. carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).
To better describe the magnitude and patterns of these greenhouse gases, in 2019 we developed an automated system for continuous in situ greenhouse gas measurements. The system, set up in Paracou (French Guiana), was a combination of soil chambers connected to two gas analysers running in parallel (Courtois et al. 2019) and stem chambers, an original extension consisting of a flexible custom-made chamber system (Fig. 3). Our system worked well in the warm and extremely humid environment of a tropical forest.
In Bréchet et al. (2021), we present the results over an eleven-month period, which captured the seasonal and diel variations of stem and soil CO2 and, to a lesser extent, CH4 and N2O fluxes. We observed a circadian rhythm in stem CO2 efflux, as expected from temperature-driven Arrhenius kinetics. Opposite diel patterns between stem CO2 efflux and that of an adjacent soil site were also observed, suggesting that in tropical forests, stem and soil respiration physiology are not necessarily driven by the same environmental factors. These preliminary results did not show clear circadian rhythms for CH4 and N2O in either soil or stem, also indicating decoupled regulation from that of diel CO2 effluxes.
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Figure 3
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Bréchet et al. 2021; doi: 10.1111/nph.17352
Related studies: Courtois et al. 2019; Daniel et al. 2023
Related studies: Courtois et al. 2019; Daniel et al. 2023
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④① Combining effect of nutrient availability and drought on soil greenhouse fluxes in tropical forests
In Bréchet et al. (2019) (CEBA, IMBALANCE-P project), we showed marked differences in the responses of soil carbon dynamics depending on whether nutrients and water were applied or withheld as single or combined treatments. The differences were i) a positive effect of nitrogen and phosphorus additions, mitigated by soil water content via imposed drought conditions, for CO2 efflux, and ii) a positive and strong effect of soil water content for CH4 flux. Surprisingly, fertilisation only affected soil CO2 efflux, and drought caused soil to become a source of CH4 rather than a sink (orange arrows and dash circle on Fig. 2). These results suggest that changes in soil nutrient and water content most likely influence the complex processes of CO2 and CH4 exchange, which are controlled by multiple biophysical and biogeochemical conditions, e.g. methanotrophic activities. For both soil fluxes, we found that resilience is slow and should be studied over long time periods. As an important finding, we highlighted that in tropical forest ecosystems, nutrient and water availability, both of which are expected to be affected by climate change, can dramatically affect soil greenhouse gas fluxes. |
Figure 2
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Bréchet et al. 2019; doi: 10.3389/fenvs.2019.00180
Related studies: Courtois et al. 2018; Van Langenhove et al. 2019; Van Langenhove et al. 2021; Li et al. 2021; Talle Verryckt et al. 2022; Llusia et al. 2022, Vallicrosa et al. 2023; Peguero et al. 2023; Figueiredo Lugli et al. 2023
Related studies: Courtois et al. 2018; Van Langenhove et al. 2019; Van Langenhove et al. 2021; Li et al. 2021; Talle Verryckt et al. 2022; Llusia et al. 2022, Vallicrosa et al. 2023; Peguero et al. 2023; Figueiredo Lugli et al. 2023
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④①② Studying priming effects to predict carbon release from forest soils: a new cross continental approach
To our knowledge, our study (Bréchet et al. 2018; FORESTPRIME project) was the first large-scale experiment comparing the effects of altered aboveground litter inputs on soil respiration across distinct climatic zones.
To our knowledge, our study (Bréchet et al. 2018; FORESTPRIME project) was the first large-scale experiment comparing the effects of altered aboveground litter inputs on soil respiration across distinct climatic zones.
We demonstrated that although the occurrence of priming effects at our study sites largely tracked the seasonal dynamics of litterfall and soil respiration, the timing, frequency and magnitude of soil carbon release by priming were harder to predict (Fig. 1).
In contrast to our original hypothesis, soil carbon release by priming was more consistent and occurred more frequently in the temperate woodland, which may be a result of slower carbon turnover.
Our results contribute to understanding in situ priming effects in different forest ecosystems, and further work is needed to identify the underlying mechanisms.
Bréchet et al. 2018; doi: 10.1002/ece3.3945
Related studies: Laird-Hopkins et al. 2017; Lopez-Sangil et al. 2017; Kerdraon-Byrne et al. 2019; Sayer et al. 2019; Sayer et al. 2020
In contrast to our original hypothesis, soil carbon release by priming was more consistent and occurred more frequently in the temperate woodland, which may be a result of slower carbon turnover.
Our results contribute to understanding in situ priming effects in different forest ecosystems, and further work is needed to identify the underlying mechanisms.
Bréchet et al. 2018; doi: 10.1002/ece3.3945
Related studies: Laird-Hopkins et al. 2017; Lopez-Sangil et al. 2017; Kerdraon-Byrne et al. 2019; Sayer et al. 2019; Sayer et al. 2020
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①② Using a rapid and non-destructive approach, electromagnetic induction, to map the heterogeneity of soil properties and study forest structure
In Bréchet et al. (2012), we investigated tree-soil relationships in tropical forests using the electromagnetic induction technique and showed that it was a promising method for mapping spatial variation in soil texture in forest and plantation ecosystems.
This technique also allows us to detect the effect of soil water repellency, a naturally occurring phenomenon, on wetting patterns in native tropical forests.
In Bréchet et al. (2012), we investigated tree-soil relationships in tropical forests using the electromagnetic induction technique and showed that it was a promising method for mapping spatial variation in soil texture in forest and plantation ecosystems.
This technique also allows us to detect the effect of soil water repellency, a naturally occurring phenomenon, on wetting patterns in native tropical forests.
Bréchet et al. 2012; doi: 10.2136/vzj2011.0102
Related study: Wuddivira et al. 2012
Related study: Wuddivira et al. 2012
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