Biophilic plant design: (Nano)Fertilising barley in hydroponics for ‘lush space gardens’

Plant growth in space goes beyond nutrition, it enhances well-being by connecting humans to nature through biophilic design. Nutrient stress is a major constrain in Space. This study used barley as a model plant in non-circulating hydroponics with varying nitrogen levels to simulate space nutrient stress conditions and test nano-fertiliser technology. Nitrogen-doped carbon quantum dots were applied in solution (hydroponics) and sprayed (aeroponics) to alleviate stress and keep the plant attractive under Space stress. The leaves' greenness was assessed using the soil plant analysis development (SPAD) during plant growth. The study found that plants grown under ‘high nitrogen’ (1 mM) conditions had higher SPAD and shoots-to-roots ratio (S/R) could reach as high as 31, and 3.2, respectively. In contrast, ‘low nitrogen’ grown plants were less green and bushy, wherein the SPAD and S/R were 11.2 and 1.03, respectively. The foliar fertilisation (FF) treatment turned out to be effective for the biophilic parameters, provided it started early, i.e. after one-week of plant growth. Applying an FF after two weeks was found to be less effective because the fresh S/R increased from 1.93 to 2.94. The FF treatment slightly increased the SPAD for the ‘low nitrogen’ sample by comparison to the control sample (no FF). Regardless of the treatment, the fresh shoot weight decreased under ‘low nitrogen’, except when being boosted by a high concentration (100 mg/l) of the nano-fertiliser quantum dots. Nonetheless, the fresh shoot weight of ‘low nitrogen’ growth was almost identical to ‘high nitrogen’ growth, which were 1.88 g and 2.20 g, respectively. These findings epitomise the potential of the nano fertiliser to reduce nitrogen use in plants. The results from the best experimental data gathered (greenness, shoots/roots, leaf number/shape) were implemented in a visualisation of an early-stage idea for the Spaceship interior using an artificial intelligence (AI) SDXL 1.0 model. Plant growth experiments in a home-built spacecraft replica confirmed that the use of LN (0.5 mM) conditions can be favourably used under ‘real-space conditions’ and that the nitrogen-doped carbon quantum dot nanofertiliser is effective for creating biophilic SPAD value.