Carbonyl sulphide (COS) is a trace gas that can be used to estimate plant CO₂ uptake. For this, the ratio of deposition velocities of COS and CO₂ (leaf relative uptake - LRU) is relevant. We use a soil – canopy – atmospheric mixed layer model to simulate COS and CO₂ plant uptake in needleleaf ecosystems, and derive LRU. We find significant in-canopy variability of LRU, and develop a regression model for canopy-scale LRU. The results can contribute to improving COS-based ecosystem plant CO₂ uptake estimates in needleleaf forests.