S06 - Session O3 - Continuous and dynamic illumination induce divergent water transport dynamics, growth and development in sweet pepper (Capsicum annuum L.).

Authors: Simon Lauwers *, Elise Tardy, Jonas Coussement, Kathy Steppe

The study of light emitting diodes (LEDs) as supplemental light and as steering light for sweet pepper ( Capsicum annuum L.) is widely covered with focus on three main aspects: light quality, light quantity and photoperiod. In this study, a new light fixture was used, fitted with a cluster of 13 different types of LEDs, allowing automated control of light intensity of the different LEDs every 15 minutes. This fixture makes it possible to change light quality and quantity throughout the day. In this study, plant responses to a continuous illumination scheme were compared to a bell-shaped one. Effects on morphological parameters were substantiated with water transport dynamics in the plants. Sweet pepper plants were grown in growth chambers under a broad light spectrum, allowing maximal light intensity of the fixtures and maximal light efficiency in the plants. Control plants received a continuous light intensity of 291.5 µmol.s -1 .m -2 , whereas plants in a second growth chamber received a bell-shaped illumination scheme with intensities ranging from 32.7 µmol.s -1 .m -2 to 382.4 µmol.s -1 .m -2 . Both treatments had a photoperiod of 18 h and had an equal daily light integral of 18.7 mol.day -1 .m -2 . During the experiment, sap flow rate, stem diameter variations and leaf thickness variations were continuously monitored. Plants that were exposed to continuous illumination invested more resources in generative growth, while plants exposed to bell-shaped illumination showed vegetative growth. The generative or the vegetative state of the plant was most likely due to a difference in flower and fruit abortion rates. Between both treatments, clear differences in water transport dynamics were observed, which were argued to respond to the generative or vegetative state of the plants. Illumination schemes may therefore play an important role in the environmental manipulation of crop growth and development.