Optimising the greenhouse cultivation of Lotus japonicus under dimmable LED

Abstract

Legumes are important crops as a source of plant‐based proteins, and their independence of nitrogen fertilizers reduces the carbon footprint of cropping systems. Within the family, Lotus japonicus is an important model system for research on arbuscular mycorrhiza and root nodule symbiosis. Genetic approaches require year‐round reproducible growth and seed production. Thus, we aimed to optimise the cultivation system of L. japonicus in a modern research greenhouse with dimmable LEDs while reducing energy consumption. Dimmable LEDs allow us to regulate the light provided by energy‐consuming lamps in response to the ambient light intensities to achieve constant daily light integrals (DLIs) for the plants inside the greenhouse. The use of moving lamps can further reduce the number of LEDs per area, provided the cultivated species tolerates light fluctuations. In our study, we compared the plant development and the seed production during spring/summer and autumn/winter in two ecotypes (Gifu B‐129, MG‐20). Plants were cultivated under stationary or moving LEDs with two fertilisation schemes and two seed pre‐treatments. Heat‐treatment of the seed had no negative effect on the germination rate and the plant development and can be recommended as a standard hygiene procedure. The weekly fertilisation of L. japonicus can be replaced by adding slow‐release fertilizer at the start of the cultivation. Cultivation on increased micro‐ or macronutrient supply did not increase pod yield; we thus conclude that the plants were not nutrient limited. L. japonicus developed more slowly and produced lower yields in the fluctuating light of moving LEDs than under stationary LEDs. The difference was enhanced during times of low ambient light intensities. As previously observed, Gifu developed more slowly than MG‐20. While the reduced initial growth rate in the first weeks may be caused by the lower seed weight of Gifu, the delay in subsequent development seemed to result from a higher sensitivity of Gifu to low light intensities and light intensity fluctuations, as the difference between the ecotypes decreased with increasing DLI. In conclusion, we developed an optimised cultivation system for L. japonicus in a climate‐controlled greenhouse by dimming LED in response to ambient light intensities to achieve a DLI of 20 to 25 mol m ⁻²  d ⁻¹ .