Periodic Reporting for period 1 - OASIS (Optimizing the Adsorption of water vapour to enhance the Sequestration of Inorganic carbon and phototrophs activity in dry Soils)
Berichtszeitraum: 2024-01-01 bis 2025-12-31
Dryland ecosystems cover a substantial fraction of the Earth’s land surface and are projected to expand under climate change. Despite their global importance, their role in carbon and water cycling remains highly uncertain, partly due to challenges associated to measuring and understanding abiotic fluxes in extremely dry conditions and episodic biological activity. Improving the understanding of carbon storage and vulnerability in these systems is therefore essential for both climate mitigation and adaptation strategies.
The OASIS project was initially motivated by the hypothesis that atmospheric water vapour adsorption could influence soil carbon dynamics in dry environments, potentially interacting with mineral processes such as carbonation. In this context, enhanced rock weathering was considered as a possible strategy to increase reactive mineral surfaces and promote inorganic carbon sequestration. At the same time, drylands are often dominated by vegetation adapted to water limitation, such as CAM plants, whose contribution to ecosystem-scale carbon fluxes remains insufficiently captured by conventional monitoring approaches.
During the course of the project, it became evident that a major scientific bottleneck lies in the capacity to robustly observe and disentangle the different biological and physical processes contributing to soil–plant–atmosphere exchanges under dry conditions. The project pathway was therefore reoriented towards establishing a robust experimental framework to quantify the relative magnitude of carbon and water flux components, assess ecosystem responses to climate extremes, and evaluate the vulnerability and potential of dryland ecosystems as carbon sinks.
The OASIS project was initially motivated by the hypothesis that atmospheric water vapour adsorption could influence soil carbon dynamics in dry environments, potentially interacting with mineral processes such as carbonation. In this context, enhanced rock weathering was considered as a possible strategy to increase reactive mineral surfaces and promote inorganic carbon sequestration. At the same time, drylands are often dominated by vegetation adapted to water limitation, such as CAM plants, whose contribution to ecosystem-scale carbon fluxes remains insufficiently captured by conventional monitoring approaches.
During the course of the project, it became evident that a major scientific bottleneck lies in the capacity to robustly observe and disentangle the different biological and physical processes contributing to soil–plant–atmosphere exchanges under dry conditions. The project pathway was therefore reoriented towards establishing a robust experimental framework to quantify the relative magnitude of carbon and water flux components, assess ecosystem responses to climate extremes, and evaluate the vulnerability and potential of dryland ecosystems as carbon sinks.
OASIS combined methodological developments with mesocosm and field experiments to investigate soil–plant–atmosphere exchanges in arid and semi-arid ecosystems. A key achievement was the development and deployment of a multi open dynamic chamber system allowing continuous measurements of CO2 and water vapour fluxes under very low soil moisture conditions, where conventional approaches often face strong limitations.
Experiments were conducted on both bare soils and vegetated systems representative of dryland environments, with particular emphasis on drought-adapted vegetation, including plants with a Crassualcean Acid Metabolism (CAM) photosynthetic pathway that absorbs CO2 during nightime. Measurements were designed to capture diel dynamics and to provide a quantitative partitioning of net fluxes into their main components. For CO2, this included distinguishing photosynthetic uptake from respiratory losses, as well as separating autotrophic and heterotrophic respiration. For water vapour, exchanges were analysed by differentiating evaporation, plant transpiration, and atmospheric water vapour adsorption.
A specific focus was placed on nocturnal fluxes, which are particularly relevant for CAM-dominated ecosystems. Current in situ approaches, such as eddy covariance, are known to face limitations at night due to low atmospheric turbulence and reduced sensitivity, particularly under dry conditions where fluxes are often of low magnitude and occur as short-lived pulses that are challenging to capture. The mesocosm-based “dryland ecosystem analog” developed in OASIS provided a controlled framework to capture these nocturnal exchanges and to explore flux dynamics that remain difficult to resolve in the field.
The experimental framework also included the simulation of climate change scenarios, notably heat waves and extreme rainfall events. These manipulations revealed strong and rapid responses of both carbon and water fluxes, highlighting the sensitivity of dryland ecosystems to climatic extremes.
Within the experimental configuration of the project, biological CO2 fluxes associated with vegetation activity and soil respiration dominated observed signals. Geochemical fluxes, such as those potentially related to mineral carbonation, were comparatively small in magnitude and could not be resolved relative to biological variability and instrumental uncertainty.
Experiments were conducted on both bare soils and vegetated systems representative of dryland environments, with particular emphasis on drought-adapted vegetation, including plants with a Crassualcean Acid Metabolism (CAM) photosynthetic pathway that absorbs CO2 during nightime. Measurements were designed to capture diel dynamics and to provide a quantitative partitioning of net fluxes into their main components. For CO2, this included distinguishing photosynthetic uptake from respiratory losses, as well as separating autotrophic and heterotrophic respiration. For water vapour, exchanges were analysed by differentiating evaporation, plant transpiration, and atmospheric water vapour adsorption.
A specific focus was placed on nocturnal fluxes, which are particularly relevant for CAM-dominated ecosystems. Current in situ approaches, such as eddy covariance, are known to face limitations at night due to low atmospheric turbulence and reduced sensitivity, particularly under dry conditions where fluxes are often of low magnitude and occur as short-lived pulses that are challenging to capture. The mesocosm-based “dryland ecosystem analog” developed in OASIS provided a controlled framework to capture these nocturnal exchanges and to explore flux dynamics that remain difficult to resolve in the field.
The experimental framework also included the simulation of climate change scenarios, notably heat waves and extreme rainfall events. These manipulations revealed strong and rapid responses of both carbon and water fluxes, highlighting the sensitivity of dryland ecosystems to climatic extremes.
Within the experimental configuration of the project, biological CO2 fluxes associated with vegetation activity and soil respiration dominated observed signals. Geochemical fluxes, such as those potentially related to mineral carbonation, were comparatively small in magnitude and could not be resolved relative to biological variability and instrumental uncertainty.
OASIS advances the state of the art by moving beyond net flux measurements towards a process-based understanding of carbon and water exchanges in dryland ecosystems. By explicitly addressing the partitioning of CO2 and water vapour fluxes, the project provides new insights into the mechanisms controlling ecosystem functioning under extreme water limitation and variations of ambient conditions, including periods of simulated water vapour adsorption.
The results highlight the central role of vegetation, particularly drought-adapted plants such as CAM species, in regulating carbon uptake and release. By enabling the quantification of nocturnal carbon assimilation under controlled dryland conditions, the project suggests that carbon uptake by CAM-dominated ecosystems may be underestimated by current field-based monitoring approaches, and by their underrepresentation in global datasets. The experimental framework also allows the coexistence and interaction of multiple carbon fixation pathways, including CAM, C₃ and C₄ vegetation, as well as biocrust activity, to be explored in an integrated manner.
The climate manipulation experiments further demonstrate that while dryland ecosystems can sustain net carbon uptake under extremely dry conditions due to the photosynthesis of drought-adapted plants, their functioning is highly sensitive to rapidly fluctuating environmental variables and climatic extremes such as heat waves and intense rainfall events. These findings emphasise both the carbon storage capacity of dryland ecosystems and their vulnerability under future climate scenarios.
Importantly, the project clarifies that within the experimental set-up used, biological processes dominate short-term carbon fluxes, while geochemical contributions were of lower magnitude. By focusing on relative flux contributions rather than assumed detectability, OASIS provides a realistic foundation for future experimental designs, improved observation strategies, and more accurate representation of dryland carbon cycling.
The results highlight the central role of vegetation, particularly drought-adapted plants such as CAM species, in regulating carbon uptake and release. By enabling the quantification of nocturnal carbon assimilation under controlled dryland conditions, the project suggests that carbon uptake by CAM-dominated ecosystems may be underestimated by current field-based monitoring approaches, and by their underrepresentation in global datasets. The experimental framework also allows the coexistence and interaction of multiple carbon fixation pathways, including CAM, C₃ and C₄ vegetation, as well as biocrust activity, to be explored in an integrated manner.
The climate manipulation experiments further demonstrate that while dryland ecosystems can sustain net carbon uptake under extremely dry conditions due to the photosynthesis of drought-adapted plants, their functioning is highly sensitive to rapidly fluctuating environmental variables and climatic extremes such as heat waves and intense rainfall events. These findings emphasise both the carbon storage capacity of dryland ecosystems and their vulnerability under future climate scenarios.
Importantly, the project clarifies that within the experimental set-up used, biological processes dominate short-term carbon fluxes, while geochemical contributions were of lower magnitude. By focusing on relative flux contributions rather than assumed detectability, OASIS provides a realistic foundation for future experimental designs, improved observation strategies, and more accurate representation of dryland carbon cycling.