Whole-plant gas-exchange performance of chlorina and TM2016 mutants under different light and CO2 conditions.

Gas-exchange analyses were performed on plants grown at the University of Tartu. Seeds were placed between wet tissue papers and germinated at room temperature, in darkness, for 2-3 days, and transferred on peat:vermiculite:water (4:2:3) growth substrate. Plants were grown at 530 μmol photons m−2 s−1 (PPFD) for 16 h light/8 h dark. Day/night temperatures were set to 20/18 °C, with a relative humidity of 60%. Plants were watered uniformly throughout the experiment and analysed at 16 DAS. Whole-plant gas exchange was measured using the Jyrkki MAX system (Plant Invent). Prior to analysis, four plants of the same genotype were placed in individual measuring chambers and allowed to acclimate for 1–3 h to stabilize their metabolic activity. Measurements were performed sequentially under ambient CO2 concentration (≈ 420 ppm; Ci) and moderate irradiance (600 μmol photons m−2 s−1; PPFD), under high irradiance (1200 μmol photons m−2 s−1; PPFD), and under high irradiance combined with elevated CO2 concentration (≈ 800 ppm; Ci). Net CO2 assimilation rate, stomatal conductance, and instantaneous water-use efficiency (iWUE) were recorded under each condition.