In contrast to the primary metabolism, responsible for essential synthesis mechanisms and mass balance in plants, the secondary metabolism is not of particular importance for each cell but for the plant organism as its whole. Most of these metabolites show antioxidant properties and are beneficial for human health. In order to affect accumulation of those metabolites, light is an essential factor. It is possible to select various combinations of light intensity and light quality to address corresponding photoreceptors and synthesis. However, the plethora of additional variables considering environmental conditions such as temperature, relative humidity or cultivation method complicate defining specific "light recipes". This review summarizes experiments dealing with consumable leafy greens such as lettuce or basil and the enhancement of three selected metabolites-anthocyanins, carotenoids and flavonols.

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Within this paper, the authors explain their transdisciplinary vision of nutrient recovery for sustainable urban plant cultivation in Germany from different but complementary perspectives (SUSKULT vision). Nowadays, the demand for fresh, healthy, locally and sustainably produced food in German urban areas is constantly increasing. At the same time, current agricultural systems contribute significantly to exceeding the planetary boundaries. The disruption of the phosphorus and nitrogen cycles in particular stands out from the manifold effects of modern food production on the Earth system. One central issue that will have to be faced in the future is how increased yields in agriculture will be achieved with high-energy requirements in fertilizer production and pollution of water and soil by phosphorus and reactive nitrogen. City region food systems (CRFS) can be a solution to overcome these issues. Nevertheless, to ensure sustainable CRFS, innovative technologies and methods need to be developed, including nutrient and energy recovery and adapted horticultural cultivation methods that fit complex urban dynamics. Such new strategies need to be integrated in long-term social and political transformation processes to enhance acceptance of food produced by recyclates. The joint contribution of experts from the wastewater, horticultural, and political sciences, together with industrial and societal sector actors, is critical to reach these objectives. The overarching goal of SUSKULT’s vision is the establishment of the field of urban circular agricultural production as an innovative sector of the bio-based economy in Germany.

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