Adaptive photosynthetic in drought-resistant and susceptible Jerusalem artichoke genotypes under elevated CO₂ and light intensity during drought stress

Under elevated (relative to ambient) light intensity and CO₂ levels combined with drought affect photosynthesis, with responses may be varying between genotypes depending on their drought resistance. Thus, this study aimed to determine the difference of light intensity and CO2 concentration on the photosynthetic traits of Jerusalem artichoke genotypes differing in drought resistance under drought conditions. The rising CO₂ concentrations enhanced photosynthetic rate (Pn) and transpiration efficiency (TE), but decreased stomatal conductance (gs) and transpiration rate (E) in both genotypes. The highest Pn was observed at 1,000 µmol mol⁻¹ CO₂ for drought-resistant genotype JA 60 and at 1500 µmol mol⁻¹ CO₂ for drought-susceptible genotype KT 2. Additionally, rising photosynthetic photon flux density (PPFD) levels improved Pn, gs, and E under both water levels, with optimal responses recorded at 2500 µmol m⁻² s⁻¹ PPFD for both genotypes. In drought-resistant genotype, TE increased with rising PPFD up to 1500 µmol m⁻² s⁻¹ while the drought-susceptible genotype peaked at 1000 µmol m⁻² s⁻¹, after which TE declined under drought. The drought-resistant genotype demonstrated more efficient stomatal regulation, higher photosynthetic capacity, greater transpiration efficiency and better maintenance of leaf area and biomass under drought stress, whereas the susceptible genotype showed weaker control over these physiological and growth-related traits. Drought-tolerant JA 60 and drought-sensitive KT 2 exhibited contrasting physiological strategies. JA 60 maintained consistently high Pn, gs, and E across all CO₂ and light conditions and retained leaf area and biomass under drought, whereas KT 2 showed reduced photosynthesis and greater declines in leaf area and biomass under drought conditions, but showed higher TE. Despite these differences, both genotypes displayed common responses, including decreased gs under elevated CO₂, enhanced TE during water stress, and increased Pn with higher light intensity. The strong performance of JA 60 under combined stresses suggests its suitability for cultivation in water-limited environments, whereas the water-saving strategies of KT 2 provide valuable insights for breeding programs aimed at enhancing TE.