Blue light enrichment accelerates photosynthetic induction under contrasting environmental conditions in wheat.

In nature, leaves often undergo transient increases in light intensity. Slow stomatal and biochemical responses restrict CO2 diffusion and fixation during these transitions, delaying photosynthetic induction and lowering light use efficiency. As blue light (BL) efficiently promotes stomatal opening, it has been hypothesized that BL enrichment could alleviate diffusional limitations and accelerate photosynthetic induction. Yet, existing evidence is inconsistent and a comprehensive assessment is needed. Gas exchange during consecutive transitions from darkness to low light (LL), LL to high light (HL), and postillumination was measured in wheat leaves under three to six levels of BL fraction in moderate and adverse environments, including high measurement vapor pressure deficit, elevated measurement CO2 concentrations, and progressive drought. Blue light enrichment accelerated photosynthetic induction in a dose-dependent manner by reducing both diffusional and biochemical limitations. Multi-level mechanisms, such as stomatal behavior and transcriptional adjustments, contributed to reducing diffusional limitations. The acceleration of photosynthetic induction by BL enrichment persisted in adverse environments. Compared with the BL-free condition, BL enrichment enhanced photosynthetic carbon gain during the HL induction by up to 60%. These results suggest that BL-induced stomatal opening is crucial for photosynthetic performance in fluctuating light environments.