Growing Media Amendments and LED Light Interaction effect on Microgreens Plant Growth and Biochemical Composition

Abstract

The key preharvest factors that can affect the edible quality of microgreens are genotypic characteristics, growing media, climate, and management practices. Microgreens are immature plants of vegetables, herbs, or even wild species grown for their high amount of biochemical compounds, mineral nutrients, and high potential biological functions. Microgreens are delicate and responsive to varying cultivation conditions. The presented study focuses on the formulation and assessment of the impact of different proportions of mixed growing media amendments and the interactive effects of different blue: red ratios of LED light on plant growth indices and biofunctional properties of different microgreen species. In the first three experiments, the optimum mixed growing media for microgreens production was developed and the efficacy of two different sources of mushroom compost including White oyster mushroom compost (MC1) and Shiitake mushroom compost was tested. The growth and yield performance of the microgreens were enhanced in growing media that consisted of shiitake mushroom compost. The shiitake-based media improved the physicochemical properties of the mixed growing media. In the fourth experiment, the best media from the previous experiment were selected for optimization to improve porosity and drainage by substitution of mushroom compost with PittMoss. Growing medium containing mushroom compost was the most effective growing medium to increase microgreens plant growth, yield, and biochemical composition, as compared to the PittMoss-based medium. The final experiment (Experiment 5) evaluated the interaction between the best two selected growing media and different ratios of blue: red LED light on the growth and quality of microgreens. Growth and yield parameters of microgreens grown in media containing sawdust were enhanced by a larger red fraction of light. Biochemical compositions and antioxidant capacity in those plants grown in media containing PittMoss under a slightly higher proportion of red LED light can be associated with the growth-defense trade-off mechanism. Overall, the results of this thesis suggest that the application of natural growing media and the combination of blue and red LEDs have a vital role in increasing crop phytonutrients of human health benefits. Based on our findings, we suggest that growing media containing PittMoss and a specific 40blue: 60red ratio can be a suitable alternative to conventional media for growing microgreens to improve productivity and biochemical compounds.