Cross-Ecosystem Patterns in Carbonyl Sulfide Exchange

Gross primary production (GPP) is a key driver of the terrestrial carbon cycle, yet it cannot be directly measured at the ecosystem scale. Carbonyl sulfide (COS) has emerged as a promising tracer for GPP because it shares the same leaf-level diffusion pathway as CO₂ and is, with negligible re-emission, irreversibly taken up by plants through carbonic anhydrase. As a result, ecosystem-scale COS fluxes provide an independent constraint on photosynthetic CO₂ uptake and offer new opportunities to evaluate and refine GPP estimates derived from eddy covariance and modeling approaches. However, uncertainties remain regarding how vegetation type, canopy structure, and environmental conditions modulate COS uptake across ecosystems. In particular, the leaf relative uptake rate (LRU) of COS and CO₂ deposition velocities, commonly used to infer GPP from COS fluxes, varies across species and depends on factors such as photosynthetic active radiation and vapor pressure deficit.

Here, we present a multi-site synthesis of ecosystem-scale COS exchange measurements spanning a broad range of vegetation types and climatic conditions, including savanna (Quercus ilex), temperate mountain grassland, agricultural cropland (Glycine max.), temperate deciduous forest (Fagus sylvatica), and temperate coniferous forest (Pinus sylvestris). These sites differ markedly in plant functional types, leaf morphology, phenology, canopy structure, and typical environmental forcing, providing an ideal framework to investigate controls on COS uptake across ecosystems.

All COS fluxes are derived using eddy covariance measurements and processed with a unified workflow using the EddyUH software, ensuring methodological consistency across sites and enabling robust cross-ecosystem comparisons without confounding effects from data processing choices. This harmonized approach allows us to focus on ecosystem-specific drivers rather than methodological artifacts.

Our analysis explores how differences in plant species influence COS uptake dynamics, and how these interact with environmental drivers such as photosynthetically active radiation, vapor pressure deficit, air temperature and soil moisture.

The results presented will provide new insights into ecosystem-specific COS exchange behavior and its implications for using COS as a tracer for GPP across heterogeneous landscapes. Ultimately, this work aims to improve our understanding of how vegetation and climate jointly regulate COS fluxes and to support the broader application of COS-based approaches for constraining ecosystem-scale photosynthesis.