Heavy payloads in future shuttle journeys to Mars present limiting factors, making self-sustenance essential for future colonies. Therefore, in situ resources utilization (ISRU) is the path to successful and feasible space voyages. This research frames the concept of planting leafy vegetables on Mars regolith simulant, ameliorating this substrate’s fertility by the addition of organic residues produced in situ. For this purpose, two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova^®) were chosen to be cultivated in four different mixtures of MMS-1 Mojave Mars simulant:compost (0:100, 30:70, 70:30 and 100:0; v:v) in a phytotron open gas exchange growth chamber. The impact of compost rate on both crop performance and the nutritive value of green- and red-pigmented cultivars was assessed. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use efficiency and quality traits of lettuce. In particular, red Salanova^® showed the best performance in terms of these quality traits, registering 32% more phenolic content in comparison to 100% simulant. Nonetheless, the 70:30 mixture represents a more realistic scenario when taking into consideration the sustainable use of compost as a limited resource in space farming, while still accepting a slight significant decline in yield and quality in comparison to the 30:70 mixture.

Hydroponics growing systems often contain excessive nutrients (especially nitrates), which could lead to a quality loss in ready-to-eat leafy vegetables and posing a health risk to consumers, if managed inadequately. A floating raft system was adopted to assay the production and quality performance of lettuce (Lactuca sativa L. cv ‘Maravilla De Verano Canasta’) deprived of the nutrient solution by replacement with only water, three and six days before harvest. Yield and quality parameters, mineral composition, pigments, organic acids, amino acids profile, soluble proteins, and carbohydrate content were determined. Nutrient solution deprivation six days before harvest resulted in a significant reduction in leaf nitrate (−53.3%) concomitant with 13.8% of yield loss, while plants deprived of nutrient solution three days before harvest increased total phenols content (32.5%) and total ascorbic acid (102.1%), antioxidant activity (82.7%), anthocyanins (7.9%), sucrose (38.9%), starch (19.5%), and γ-aminobutyric acid (GABA; 28.2%), with a yield reduction of 4.7%, compared to the control. Our results suggest that nutrient solution deprivation three days before harvest is a successful strategy to reduce nitrate content and increase the nutritional quality of lettuce grown in floating raft systems with negligible impact on yield. These promising results warrant further investigation of the potential effect of nutrient solution deprivation on the quality attributes of other leafy vegetables cultivated in floating raft systems and in a “cascade” growing system.

To make feasible the crewed missions to the Moon or Mars, space research is focusing on the development of bioregenerative life support systems (BLSS) designed to produce food crops based on in situ resource utilisation (ISRU), allowing to reduce terrestrial input and to recycle organic wastes. In this regard, a major question concerns the suitability of native regoliths for plant growth and how their agronomic performance is affected by additions of organic matter from crew waste. We tested plant growth substrates consisting of MMS-1 (Mars) or LHS-1 (Lunar) simulants mixed with a commercial horse/swine monogastric manure (i.e., an analogue of crew excreta and crop residues) at varying rates (100:0, 90:10, 70:30, 50:50, w/w). Specifically, we measured: (i) lettuce (Lactuca sativa L. cultivar ‘Grand Rapids’) growth (at 30 days in open gas exchange climate chamber with no fertilisation), plant physiology, and nutrient uptake; as well as (ii) microbial biomass C and N, enzymatic activity, and nutrient bioavailability in the simulant/manure mixtures after plant growth. We discussed mechanisms of different plant yield, architecture, and physiology as a function of chemical, physico-hydraulic, and biological properties of different substrates. A better agronomic performance, in terms of plant growth and optically measured chlorophyll content, nutrient availability, and enzymatic activity, was provided by substrates containing MMS-1, in comparison to LHS-1-based ones, despite a lower volume of readily available water (likely due to the high-frequency low-volume irrigation strategy applied in our experiment and foreseen in space settings). Other physical and chemical properties, along with a different bioavailability of essential nutrients for plants and rhizosphere biota, alkalinity, and release of promptly bioavailable Na from substrates, were identified as the factors leading to the better ranking of MMS-1 in plant above and below-ground mass and physiology. Pure Mars (MMS-1) and Lunar (LHS-1) simulants were able to sustain plant growth even in absence of fertilisation, but the amendment with the monogastric manure significantly improved above- and below-ground plant biomass; moreover, the maximum lettuce leaf production, across combinations of simulants and amendment rates, was obtained in treatments resulting in a finer root system. Increasing rates of monogastric manure stimulated the growth of microbial biomass and enzymatic activities, such as dehydrogenase and alkaline phosphomonoesterase, which, in turn, fostered nutrient bioavailability. Consequently, nutrient uptake and translocation into lettuce leaves were enhanced with manure supply, with positive outcomes in the nutritional value of edible biomass for space crews. The best crop growth response was achieved with the 70:30 simulant/manure mixture due to good availability of nutrients and water compared to low amendment rates, and better-saturated hydraulic conductivity compared to high organic matter application. A 70:30 simulant/manure mixture is also a more sustainable option than a 50:50 mixture for a BLSS developed on ISRU strategy. Matching crop growth performance and (bio)chemical, mineralogical, and physico-hydraulic characteristics of possible plant growth media for space farming allows a better understanding of the processes and dynamics occurring in the experimental substrate/plant system, potentially suitable for an extra-terrestrial BLSS.

Basil (Ocimum basilicum L.) is among the most widespread aromatic plants due to its versatility of use and its beneficial health properties. This aromatic plant thrives in hydroponics, which is a valid tool to improve the production and functional quality of crops, but nevertheless, it offers the possibility to de-seasonalize production. A floating raft system was adopted to test the production and quality potential during autumn season of three different genotypes of Genovese basil (Aroma 2, Eleonora and Italiano Classico) grown in three nutrient solutions with crescent electrical conductivity (EC: 1, 2 and 3 dS m⁻¹). The aromatic and phenolic profiles were determined by GC/MS and HPLC analysis, respectively. The combination Aroma 2 and the EC 2 dS m⁻¹ resulted in the highest production, both in terms of fresh weight and dry biomass. The 2 dS m⁻¹ treatment determined the major phenolic content, 44%, compared to the other two EC. Italiano Classico showed a higher total polyphenolic content in addition to a different aromatic profile compared to the other cultivars, characterized by a higher percentage of Eucalyptol (+37%) and Eugenol (+107%) and a lower percentage of linalool (−44%). Correct management of the nutritional solution combined with adequate genetic material managed an improvement in the production and the obtainment of the desired aromatic and phenolic profiles.

In agricultural soils, thallium (Tl) of geogenic origin may represent a potential risk for human health, mainly via ingestion of food crops. In this work, a pot experiment was carried out to evaluate (1) the bioavailability of Tl and other potentially toxic elements (PTEs) in an agricultural soil with naturally occurring Tl; (2) the uptake and accumulation of PTEs in Lactuca sativa L. var. acephala, Diplotaxis tenuifolia L. DC and Silene latifolia Poir; (3) the health risks arising from plant and soil ingestion by different subpopulations and dermal contact of soil by farmers. In soil, only Tl and Pb pseudototal contents were above Italian screening values. Nevertheless, the promptly bioavailable contents of all PTEs were always below internationally recognized trigger values. Plants affected PTE bioavailability in soil by their rhizodepositions and accumulated PTEs in their shoots. Acceptable risks (hazard index < 1) arose from dietary intake of both L. sativa L., D. tenuifolia L. and dermal contact of soil by farmers. Significant health risks can derive from the intake of S. latifolia Poir. (accumulating high Tl concentrations), in particular by children (HI = 74). In conclusion, an adequate management and crop selection are needed to profitably exploit soils with geogenic Tl for agricultural purposes.