Vitale, Ermenegilda (2021) Improving photosynthetic efficiency and plant growth in controlled environments: the role of light quality, biostimulant application and ionising radiation. [Tesi di dottorato]

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The possibility of growing higher plants, especially crops, in controlled environments allows reducing the variability of plant responses to the multiple stress occurring in the field and increasing the primary production. Among variables implicated in plant development and physiology, light represents a driver. Therefore, selecting specific wavelengths of visible light to obtain appropriate light quality regimes may significantly improve photosynthesis, biomass production, and secondary metabolites synthesis, resulting in an enrichment of food quality (in terms of nutraceutical compounds and antioxidants) and plant tolerance against abiotic stresses. The use of the light quality as 'natural fertiliser' alone or combined with other eco-friendly practices such as the employment of biostimulants could be a promising solution to enhance crop productivity preserving the overexploitation of soil and reducing the overuse of agrochemicals. The light spectrum modulation within growth chambers or vertical farms may find proper applications in the cultivation of crops in extreme environments on the Earth, such as hot or cold deserts or in the Space environment. This latter is highly unhospitable because it is characterised by many unfavourable ecological factors, including microgravity and cosmic radiations. In particular, ionising radiation is one of the significant constraints preventing plant growth and survival in Space. In the Bioregenerative Life Support Systems (BLSSs), conceived to sustain human life in Space, plants will have a crucial role in food production and air regeneration and CO2 removal. Thus, in the next future, the challenge to grow plants in Space must consider studying the effect of Space ionising radiation not only on humans and animals but also on plants. The PhD project is focused on the role of light quality in regulating the photosynthetic machinery of higher plants in controlled environments. In particular, it has been explored if and how specific light wavelengths during growth may modify plant physiological behaviour and phytochemical production in response to biostimulant application or exposure to ionising radiation. Among different variables affecting plant growth, biostimulants application was selected with the specific aim to improve the overall plant physiological performance in terms of primary and secondary metabolism in the context of sustainable agricultural practices. The ionising radiation was chosen as a space stress environmental factor in the view of experiments finalised to plant cultivation in Space. The experiments were carried out on widely consumed crops such as tomato, spinach, soybean and chard, considered important functional foods. Plants were grown in dedicated growth chambers under specific temperature, relative humidity, photoperiod, and light intensity condition, modulating the light spectrum to obtain specific light regimes promoting the photosynthetic performance. The outcomes of these experiments were utilised in the subsequent trials to test how light quality combined with ionising radiation or growth-promoting agents, i.e., biostimulants, may modify photosynthesis and antioxidant production. A downscaling investigative approach was adopted to analyse plant responses at different scale levels from cells and tissues to the whole organism. The outcomes of this research may have implications not only for developing sustainable protocols for indoor cultivation but also for plant growth in extreme environments on Earth and Space, such as the orbiting stations.

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