Supplemental lighting applied within or underneath the canopy enhances leaf photosynthesis, stomatal regulation and plant development of tomato under limiting light conditions

Abstract

Intensive crop cultivation in greenhouses results in insufficient light to plants, which decreases plant photosynthesis and growth and results in reduced crop productivity and reduced economic benefit. Foliar supplemental lighting to leaves in the lower canopy is considered an effective method to cope with the stress of insufficient light on plants. Leaf photosynthesis, stomatal regulation, and growth of tomato plants were examined to estimate the effect of supplemental lighting from underneath the canopy (USL) with light orientation to the abaxial side and from the inner canopy (ISL) with light orientation to the adaxial side. Both treatments significantly improved light irradiation conditions in the lower canopy and promoted growth and photosynthesis of tomato plants. USL maintains a relatively steady light irradiation level in the lower canopy and promotes better photosynthetic and morphologic enhancement than ISL. The improved photosynthesis in plants treated with ISL resulted from larger stomatal pore area and higher stomatal conductance which enhanced carbon dioxide supply promoting photosynthetic electron transport activity. Meanwhile, USL enhanced carbon dioxide assimilation efficiency rather than stomatal morphology regulation to improve plant photosynthesis.