Abstract
Faced with today's challenges, agricultural production methods have diversified, notably with the development of controlled-environment agriculture, also known as indoor farming. This type of agriculture is highly efficient in terms of water use, but consumes large amounts of energy due to the need for artificial light. The aim of this thesis was to study the impact of photoperiod modifications to reduce lighting time and thus save energy. The effects of these modifications were studied on the agronomic parameters and physiology of pre- and post-harvest lettuces. This work is a collaboration between Avignon University and Futura Gaïa Technologies, an indoor farming company that designs and markets "turnkey" vertical farms containing horizontal axis rotary crop systems. The first task was to characterize the impact of rotation, which disrupts the perception of gravity. This disruption results in a reduction in stomatal conductance, photosystem II efficiency and net photosynthesis, but has no impact on marketable lettuce yield after 30 days of cultivation. Secondly, photoperiod modifications showed that lengthening the dark period led to a reduction in net photosynthesis as a result of disruption of the circadian rhythm of stomatal opening. The analyses thus enabled us to define the periods when the plants used light most efficiently, and to propose two new photoperiod modalities offering 12.5% and 25% savings in light hours and therefore energy. The fresh mass yield of lettuces under the '12.5%' modality is similar to that of control lettuces, thanks to better hydration, although dry mass is lower than that of control lettuces. The fresh and dry mass yields of lettuces under the '25%' modality are half those of control lettuces. Measurements of net photosynthesis as a function of time have shown that dry mass yield losses are a consequence of the phase shift between photoperiod and the circadian rhythm of stomatal opening, which alters the rhythm and reduces stomatal opening. Complementary experiments have led to the hypothesis that photoreceptors sensitive to red light (660 nm) and involved in the rhythm and intensity of stomatal opening could be used to improve light efficiency in controlled-environment agriculture. This thesis thus supports the idea of considering chronoculture, which should be combined with other energy-saving methods, to improve the sustainability of indoor farming.