ABACOS: Above- and below-canopy COS fluxes to constrain and partition forest CO2 and ET fluxes
Context
Anthropogenic climate change is affecting ecosystem functioning, in particular the biosphere-atmosphere greenhouse gas exchange. However, the response of ecosystem CO2 and evapotranspiration fluxes is still not fully understood and associated with large uncertainties. Therefore, precise flux measurements at high temporal resolution are urgently needed. The eddy covariance technique is the only direct method to measure net fluxes between the biosphere and the atmosphere. However, to improve our process understanding related to ecosystem C dynamics and evapotranspiration, these fluxes need to be reliably partitioned into gross primary productivity (GPP) and total ecosystem respiration as well as evaporation and transpiration, respectively. Different methods and approaches exist, including the use of carbonyl sulfide (COS), which can be used as a tracer for CO2 uptake, since COS is taken up by the vegetation through their stomata and hydrolysed in the leaf.
Project aims
ABACOS aims to quantify COS fluxes at different spatial and temporal scales in a temperate broadleaf forest in Switzerland, using an unprecedented integration of co-located measurements. ABACOS will provide a comprehensive assessment of different GPP constraints and evapotranspiration partitioning methods, made possible by the co-location and integrations of highly sophisticated measurements. It contributes unique COS flux data to the global COS community from a temperate mixed forest, where flux measurements and estimates of leaf relative uptake of COS are scarce. This provides the unique opportunity to evaluate the applicability of COS flux data, while improving our GPP estimates. Equally important, partitioning evapotranspiration fluxes and validating these approaches allows to estimate transpiration and improve our understanding of tree responses to environmental change. With its different approaches and cross-validations, ABACOS can be a blueprint for other projects to provide such crucial information.
Objectives
ABACOS aims to
- assess ecosystem COS fluxes, in particular forest floor contributions to the total flux,
- quantify branch and soil COS fluxes,
- constrain GPP estimates, and
- partition evapotranspiration fluxes.