Abstract
Combined drought and elevated carbon dioxide (eCO2) represent crucial facets of climate change affecting global rice (Oryza sativa L.) production. While eCO2 often stimulates photosynthesis, its interaction with water deficit remains complex and cultivar-dependent. This study utilized high-throughput chlorophyll fluorescence imaging (CFIm) to investigate the photoprotective mechanisms of two contrasting rice cultivars—IR64 (drought-sensitive) and IR74 (drought-tolerant)—under individual and combined drought and eCO2 (800 micromol mol-1) conditions. Our results demonstrated that under combined stress, IR74 maintained superior photosystem II (PSII) operating efficiency and exhibited a highly dynamic non-photochemical quenching (NPQ) response compared to IR64. High-throughput phenotyping successfully captured spatial heterogeneity in chlorophyll fluorescence across the canopy, revealing that IR74 optimized energy dissipation via the xanthophyll cycle and sustained higher photochemical quenching. Conversely, IR64 suffered severe photoinhibition, characterized by a significant decline in maximum quantum yield (Fv/Fm) and chronic upregulation of basal dissipation. These findings indicate that elevated CO2 partially mitigates drought-induced photochemical damage in a cultivar-specific manner, with tolerant cultivars better leveraging the extra carbon to maintain sink strength and photoprotective capacity. This study highlights the utility of CFIm in accelerating the screening of climate-resilient crop varieties.
