Abstract: High epicuticular wax (E_wax) content on leaves is a key trait for drought and heat stress tolerance in plants. While E_wax reduces daytime water loss by reflecting solar radiation and maintaining cooler canopy temperatures, its role in nocturnal transpiration remains less understood. Using phenomics, we identified a balance between cuticular and stomatal transpiration at night, with wax modulating these processes under varying night temperatures. Significant variability in E_wax content, nocturnal transpiration, and related morpho-physiological traits across genotypes highlights the complexity of these mechanisms. Seasonal and environmental factors, particularly temperature, strongly influence E_wax accumulation, with higher levels during warmer nights. Our data reveal a positive correlation between E_wax content and nocturnal mean transpiration rate, suggesting that genotypes with higher wax levels may open stomata to dissipate heat while minimizing water loss. Notably, genotypes with high wax content showed a lower increase in transpiration during warmer nights compared with cooler ones, indicating a regulatory role of wax under elevated temperatures. This research provides insights into the dynamics of E_wax and nocturnal transpiration, offering strategies to enhance plant resilience to rising night temperatures. Such findings are critical for breeding climate-resilient crops, advancing sustainable agriculture, and ensuring food security.

Key words: epicuticular wax, high temperature, nocturnal transpiration, phenomics, rice