Pedersen et al. describe a new amperometric CO2 microsensor and an O2 microsensor elucidated the dynamics in leaf pCO2 and pO2 during light–dark cycles for C3 Lobelia dortmanna (Campanulaceae) and CAM Littorella uniflora (Plantaginaceae) aquatic plants. During the dark period, for the C3 plant pCO2 increases, whereas for the CAM plant CO2 remains low owing to CO2 sequestration into malate.
The C3 plant becomes severely hypoxic late in the dark period whereas the CAM plant with greater cuticle permeability does not. Similar to the use of O2 microsensors to resolve questions related to plant aeration, deployment of the new CO2 microsensor will benefit plant ecophysiology research.