Airflow and spectrum interactions jointly regulate gas exchange and biomass production in vertical farming

Microclimate heterogeneity and uneven airflow remain major constraints to physiological stability and yield uniformity in vertical farming (VF). While airflow can influence leaf boundary-layer conditions and gas exchange, its interaction with LED spectral composition is not fully understood. This study investigated the combined effects of targeted airflow and LED spectrum on physiological performance and biomass formation of lettuce (Lactuca sativa L.) grown in a containerized multilayer VF system. Two lighting treatments were applied: broad-spectrum WHITE and blue-red-far-red (B/R/FR), both at a constant daily light integral (11.5 mol m^-² d^-¹; 14 h photoperiod). Targeted airflow was applied at the lower cultivation layer to modify the local canopy microclimate. Airflow significantly increased net photosynthesis under both spectra (p = 0.021), with greater enhancement under WHITE (+24%) than B/R/FR (+11%). Chlorophyll content increased in all airflow treatments (p< 0.001), while stomatal conductance decreased (p< 0.001), resulting in significantly increased intrinsic water-use efficiency (p< 0.001). Transpiration declined significantly under B/R/FR with airflow (p = 0.022), which also resulted in reduced leaf area and biomass. These findings demonstrate that airflow enhances net carbon assimilation; however, spectrum-dependent regulation of transpiration and morphogenesis determines biomass translation, highlighting the need for integrated airflow-light optimization in VF systems.