[Thesis defence] 29/03/2024, Cédric Dresch: "Energy saving in indoor agriculture: study of the effects of changes in photoperiod on agronomic parameters and the pre- and post-harvest physiology of lettuces".

Title of the thesis

"Energy saving in indoor agriculture: study of the effects of changes in photoperiod on agronomic parameters and the pre- and post-harvest physiology of lettuces".

Date and place

Oral defense scheduled on Friday 29 March 2024 at 9.00 am
Venue: CERI - Avignon University - Campus Jean-Henri Fabre 339 Chem. des Meinajaries, 84000 Avignon
Room: Amphithéâtre Blaise Pascal - CERI

Discipline

AGRONOMIC SCIENCES

Laboratory

UMR B95 - QUALISUD - An integrated approach to quality food production

Framing

• Florence CHARLES
• Huguette SALLANON

Composition of the jury

Ms Florence CHARLES	Senior Lecturer - Avignon University	Thesis supervisor
Ms Huguette SALLANON	Professor - Avignon University	Thesis co-director
Ms GAVEAU Nathalie	Professor, University of Reims Champagne-Ardenne	Rapporteur
Mr SIMONNEAU Thierry	Director of Research INRAe - Centre Occitanie-Montpellier	Rapporteur
Mr TRUFFAULT Vincent	Doctor Futura Gaïa Technologies	Thesis co-supervisor
Ms GAUTIER Hélène	INRAe Research Director	Examiner
Ms DESNOUES Elsa	Doctor CTIFL	Examiner

Summary of the thesis

Summary:

Faced with today's challenges, agricultural production methods have diversified, particularly with the development of controlled environment agriculture, also known as indoor agriculture. This type of farming is highly efficient in terms of water use, but consumes large amounts of energy because of the need for artificial light. The aim of this thesis was to study the impact of modifying the photoperiod in order to reduce the 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 agriculture company that designs and markets "turnkey" vertical farms containing horizontal axis rotary crop systems. The first task was to characterise the impact of rotation, which disturbs the perception of gravity. This disruption results in a reduction in stomatal conductance, photosystem II efficiency and net photosynthesis, but has no impact on the marketable yield of lettuce after 30 days of cultivation.

Secondly, the photoperiod modifications showed that lengthening the period of darkness led to a reduction in net photosynthesis following disruption of the circadian rhythm of stomatal opening. The analyses thus made it possible to define the periods when the plants used light most efficiently, making it possible to propose two new photoperiod modalities allowing 12.5% and 25% savings in hours of light and therefore energy. The fresh mass yield of lettuces grown under the '12.5%' method was similar to that of the control lettuces, thanks to better hydration, although the dry mass was lower than that of the control lettuces. The fresh and dry mass yields of lettuces under the '25%' modality were half those of the control lettuces. Measurements of net photosynthesis as a function of time showed that losses in dry mass yield 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 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 agriculture in a controlled environment. This thesis thus supports the idea of taking chronoculture into consideration, which should be combined with other energy-saving methods, to improve the sustainability of indoor agriculture.

Key words :
Indoor agriculture, Energy saving, Circadian rhythm, Photoperiod, Photosynthesis