Stomatal conductance and electron transport responses of finger millet (Eleusine coracana) genotypes to atmospheric carbon dioxide, vapor pressure deficit, photosynthetically active radiation, and temperature.

Climate change is intensifying environmental fluctuations that impact crop physiology, particularly in relation to water-use efficiency and stomatal and electron transport responses. Finger millet (Eleusine coracana L.), a nutrient-rich C₄ cereal cultivated in drought-prone regions, remains under-characterized regarding stomatal conductance (gsw) and electron transport (ETR) responses to dynamic field conditions. This study evaluated fifteen finger millet genotypes to assess how stomatal conductance (gsw) and transpiration rate (E), together with the fluorescence-derived photosynthetic electron transport rate (ETR), responded to key environmental drivers including carbon dioxide (CO₂) concentration, temperature, photosynthetically active radiation (PAR), and vapor pressure deficit (VPD) under both ambient and elevated CO₂ field conditions. Strong negative correlations were observed between gsw and VPD (R = -0.76), and between ETR and VPD (R = -0.90), while PAR positively influenced both gsw (R = 0.40) and ETR (R = 0.79). Elevated CO₂ reduced gsw and E across all genotypes, yet ETR remained stable, suggesting that photochemical activity was sustained despite reduced water loss. Genotype GPU-105 exhibited the steepest decline in gsw under elevated CO₂, while IC-403242 and IC-345029 retained higher conductance levels, suggesting genotypic variation in stomatal sensitivity to CO₂ concentration. These physiological patterns were visualized using heatmaps, revealing plasticity in stomatal regulation across accessions. Overall, our findings highlight genotype-specific physiological patterns that may serve as preliminary indicators for breeding programs focused on improving water-use efficiency and climate resilience in finger millet. This field-based study provides novel insights into the coordination of gas exchange and photochemical responses under realistic environmental stressors, contributing to the development of climate-smart C₄ crops.