Duckweeds can be potentially used in human and animal nutrition, biotechnology or wastewater treatment. To cultivate large quantities of a defined product quality, a standardized production process is needed. A small-scale, re-circulating indoor vertical farm (IVF) with artificial lighting and a nutrient control and dosing system was used for this purpose. The influence of different light intensities (50, 100 and 150 µmol m⁻² s⁻¹) and spectral distributions (red/blue ratios: 70/30, 50/50 and 30/70%) on relative growth rate (RGR), crude protein content (CPC), relative protein yield (RPY) and chlorophyll a of the duckweed species Lemna minor and Wolffiella hyalina were investigated. Increasing light intensity increased RGR (by 67% and 76%) and RPY (by 50% and 89%) and decreased chlorophyll a (by 27% and 32%) for L. minor and W. hyalina, respectively. The spectral distributions had no significant impact on any investigated parameter. Wolffiella hyalina achieved higher values in all investigated parameters compared to L. minor. This investigation proved the successful cultivation of duckweed in a small-scale, re-circulating IVF with artificial lighting.

In order to produce protein-rich duckweed for human and animal consumption, a stable cultivation process, including an optimal nutrient supply for each species, must be implemented. Modified nutrient media, based on the N-medium for duckweed cultivation, were tested on the relative growth rate (RGR) and crude protein content (CPC) of Lemna minor and Wolffiella hyalina, as well as the decrease of nitrate-N and ammonium-N in the media. Five different nitrate-N to ammonium-N molar ratios were diluted to 10% and 50% of the original N-medium concentration. The media mainly consisted of agricultural fertilizers. A ratio of 75% nitrate-N and 25% ammonium-N, with a dilution of 50%, yielded the best results for both species. Based on the dry weight (DW), L. minor achieved a RGR of 0.23 ± 0.009 d⁻¹ and a CPC of 37.8 ± 0.42%, while W. hyalina’s maximum RGR was 0.22 ± 0.017 d⁻¹, with a CPC of 43.9 ± 0.34%. The relative protein yield per week and m² was highest at this ratio and dilution, as well as the ammonium-N decrease in the corresponding medium. These results could be implemented in duckweed research and applications if a high protein content or protein yield is the aim.

Duckweed is gaining attention in animal nutrition and is considered as a potential alternative protein source for broiler chickens. In order to evaluate the nutritional value of duckweed, three individual batches were investigated. They consisted of a mixture of Lemna minuta and Lemna minor (A, 17.5% crude protein), Spirodela polyrhiza (B, 24.6% crude protein) and Lemna obscura (C, 37.0% crude protein). Treatment diets contained 50% batch A, 50% batch B, and 25, 50 and 75% of batch C. All diets were fed to broiler chickens (Ross 308) from an age of 21 to 27 days. Diets with a share of 50 and 75% of batch C led to decreased feed intake (109.3 and 74.9 g/day, respectively) compared to the control. Standardized ileal digestibility of crude protein and amino acids differed significantly between duckweed batches, at values for methionine between 49.9 and 90.4%. For all amino acids, batch A consistently had the lowest and batch C the highest digestibility. Batches had different tannin contents of 2943, 2890 and 303 mg/kg for batches A, B and C, respectively. The apparent ileal digestibility of phosphorus differed significantly between all batches (50.8–78.9%). Duckweed can be used as a protein feed for broiler chickens. However, a defined and stable biomass composition optimized for the requirements of broiler chickens is needed.

Root temperature has long been considered an essential environmental factor influencing the plant’s physiology. However, little is known about the effect of root temperature on the quality of the food produced by the plant, especially that of horticultural crops. To fill this gap, two independent root cooling experiments (15 °C vs. 20 °C and 10 °C vs. 20 °C) were conducted in autumn 2017 and spring 2018 in hydroponics with Chinese broccoli (Brassica oleracea var. alboglabra Bailey) under greenhouse conditions. The aim was to investigate the effect of root temperature on plant growth (biomass, height, yield) and food quality (soluble sugars, total chlorophyll, starch, minerals, glucosinolates). A negative impact on shoot growth parameters (yield, shoot biomass) was detected by lowering the root temperature to 10 °C. Chinese broccoli showed no response to 15 °C root temperature, except for an increase in root biomass. Low root temperature was in general associated with a higher concentration of soluble sugars and total chlorophyll, but lower mineral levels in stems and leaves. Ten individual glucosinolates were identified in the stems and leaves, including six aliphatic and four indolic glucosinolates. Increased levels of neoglucobrassicin in leaves tracked root cooling more closely in both experiments. Reduction of root temperature by cooling could be a potential method to improve certain quality characters of Chinese broccoli, including sugar and glucosinolate levels, although at the expense of shoot biomass.

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.

The yield and fruit quality parameters of tomatoes are influenced by environmental conditions, and cultivation systems play an important role in improving quality, apart from breeding. We examined five breeding lines and one cultivar in five cultivation systems for yield and fruit quality parameters. The cultivation systems include a single-glazed greenhouse with and without supplementary LED interlighting; a double-glazed greenhouse with and without supplementary LED interlighting; and an organic cultivation system on the field with a rainout shelter. Plants and fruits grown in the double glazing system showed significantly lower values for plant height, yield, DM, TSS, fructose, glucose, antioxidant capacity (DPPH, TEAC), TPC, calcium, phosphorus, and manganese content than in the single-glazed greenhouse, which can be explained by the lower light transmittance. However, it could be seen that the additional LED interlighting could lower the negative effect on yield and quality traits due to double glazing.