Smart glass impacts stomatal sensitivity of greenhouse Capsicum through altered light

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of <em>Capsicum</em> plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (<em>g</em>_s) or maximal (<em>g</em>_max) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K⁺ and Cl^– efflux, and Ca²⁺ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m^–2 s^–1) and high PAR (1500 µmol m^–2 s^–1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect <em>g</em>_s in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of <em>Capsicum</em> to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO₂ assimilation.