Morpho-Physiological Responses of Arabidopsis thaliana L. to the LED-Sourced CoeLux® System

Plant Growth in LED-Sourced Biophilic Environments Is Improved by the Biochar Amendment of Low-Fertility Soil, the Reflection of Low-Intensity Light, and a Continuous Photoperiod

Introducing plants in the design of biophilic indoor environments is fundamental for improving human health, well-being, and performance. Previous studies showed that the phenotype of the model plant Arabidopsis thaliana grown under LED-sourced CoeLux® lighting systems was characterized by low biomass production rates, a small leaf area, and a low lamina-to-petiole length ratio, suggesting the onset of a strong shade avoidance syndrome. Therefore, it is essential to identify new strategies to improve plant growth under these peculiar light conditions. In the present work, we investigated the effects of two growing media (i.e., low-fertility soil and soil-less substrate), solid and liquid fertilizers, manure, biochar, perlite, mirror reflection of light, and a 24 h photoperiod on A. thaliana plants growing under CoeLux® lighting systems at a light intensity of 30 μmol m-2s-1. We found that the biochar soil amendment to low-fertility soil increases both the above-ground plant biomass and leaf area. Furthermore, the application of a mirror behind the plants and a continuous photoperiod improves not only the biomass and the leaf area but also the lamina-to-petiole length ratio. The combination of different beneficial treatments can further boost plant growth in the low-intensity light environment characterizing the CoeLux® biophilic lighting systems.

Light spectra of biophilic LED-sourced system modify essential oils composition and plant morphology of Mentha piperita L. and Ocimum basilicum L

Investigating morphological and molecular mechanisms that plants adopt in response to artificial biophilic lighting is crucial for implementing biophilic approaches in indoor environments. Also, studying the essential oils (EOs) composition in aromatic plants can help unveil the light influence on plant metabolism and open new investigative routes devoted to producing valuable molecules for human health and commercial applications. We assessed the growth performance and the EOs composition of Mentha x piperita and Ocimum basilicum grown under an innovative artificial biophilic lighting system (CoeLux^®), that enables the simulation of natural sunlight with a realistic sun perception, and compared it to high-pressure sodium lamps (control) We found that plants grown under the CoeLux^® light type experienced a general suppression of both above and belowground biomass, a high leaf area, and a lower leaf thickness, which might be related to the shade avoidance syndrome. The secondary metabolites composition in the plants' essential oils was scarcely affected by both light intensity and spectral composition of the CoeLux^® light type, as similarities above 80% were observed with respect to the control light treatments and within both plant species. The major differences were detected with respect to the EOs extracted from plants grown under natural sunlight (52% similarity in M. piperita and 75% in O. basilicum). Overall, it can be speculated that the growth of these two aromatic plants under the CoeLux^® lighting systems is a feasible strategy to improve biophilic approaches in closed environments that include both plants and artificial sunlight. Among the two plant species analyzed, O. basilicum showed an overall better performance in terms of both morphological traits and essential oil composition. To increase biomass production and enhance the EOs quality (e.g., higher menthol concentrations), further studies should focus on technical solutions to raise the light intensity irradiating plants during their growth under the CoeLux^® lighting systems.

Photoreceptors’ gene expression of Arabidopsis thaliana grown with biophilic LED-sourced lighting systems

Using specific photoreceptors, plants can sense light signals fundamental to their growth and development under changing light conditions. Phytochromes sense red and far-red light, cryptochromes and phototropins sense UV-A and blue light, while the UVR8 gene senses UV-B signals. The study of the molecular mechanisms used by plants to respond to artificial biophilic lighting is of pivotal importance for the implementation of biophilic approaches in indoor environments. CoeLux® is a new lighting system that reproduces the effect of natural sunlight entering through an opening in the ceiling, with a realistic sun perceived at an infinite distance surrounded by a clear blue sky. We used the model plant Arabidopsis thaliana to assess the gene expression of the main plant photoreceptors at different light intensities and at different times after exposure to the CoeLux® light type, using high-pressure sodium (HPS) lamps as control light type. Genes belonging to different families of photoreceptors showed a similar expression pattern, suggesting the existence of a common upstream regulation of mRNA transcription. In particular, PHYA, PHYC, PHYD, CRY1, CRY2, PHOT1, and UVR8, showed a common expression pattern with marked differences between the two light types applied; under the HPS light type, the expression levels are raising with the decrease of light intensity, while under the CoeLux® light type, the expression levels remain nearly constant at a high fold. Moreover, we showed that under biophilic illumination the light spectrum plays a crucial role in the response of plants to light intensity, both at the molecular and morphological levels.