Effect of supplemental lighting on water transport, photosynthetic carbon gain and water use efficiency in greenhouse tomato

Abstract

Despite supplemental lighting is being increasingly applied in greenhouses to improve crop productivity, there have been few studies investigated effects of supplemental lighting on water movement, water consumption and water use efficiency. To examine the potentials to improve water use efficiency via supplemental lighting, photosynthetic productivity versus water movement under contrasting light treatments was investigated in greenhouse tomato (Solanum lycopersicum L.). In the present study, supplemental lighting by light-emitting diodes (LED) facilitated uniform light distributions along vertical profile canopy. The homogeneous light condition increased stomatal and mesophyll conductance for photosynthetic CO2 uptake, especially at the bottom canopy. Consequently, leaf photosynthetic capacity for carbon acquisition and assimilation was overall improved by supplemental lighting. The improvement in leaf photosynthetic capacity was more pronounced with the increased depth down the vertical profile canopy. Both shoot dry biomass and fresh fruit yield were significantly increased by supplemental lighting. Supplemental lighting by LED altered light condition solely and had no significant effect on the distribution of the water driving force along soil-plant-atmospheric continuum, water transport rate and plant water consumption. Taken together, supplemental lighting maximized photosynthetic productivity and consequently significantly increased water use efficiency, whether based of shoot dry biomass and fresh fruit yield, by 10.2% and 8.7%, respectively. Therefore, we concluded that supplemental lighting by LED is an efficient solution to improve greenhouse crop water use efficiency. The present study provides novel information improving water use efficiency without alterning water consumption for sustainable greenhouse production.