Fig 4. Overview of tree ring in 2019.

(A) The relative position of vessel lumen areas within tree ring created in 2019 with applied GAMs denoted by orange (elevated CO₂) and green characters (ambient CO₂). Microscope images of a cross-section of the 2019 annual ring of a sessile oak saplings growing in (B) ambient CO₂ glass dome and (C) elevated CO₂ glass dome. Scale bars = 200 μm.