Abstract EANA2025-85

Mars is currently the most extensively studied planet and the primary target for future human exploration and long-term settlement. The Martian surface is covered by regolith, a layer of loose, dusty material that lacks organic matter and microbiota, with physico-chemical properties unfriendly to plant growth. Nevertheless, every scenario for the long-term settlement of humans on extraterrestrial bodies includes plants as key components of bioregenerative life support systems (BLSS). To reduce reliance on Earth-based inputs, native Martian regolith could be utilized for plant cultivation. The environmental stressors may be mitigated using plant growth-promoting bacteria (PGPB). In this way, the combination of the in situ resource utilization (ISRU) approach and BLSS may enable sustainable food production in space. Therefore, the aim of this study was to investigate the potential for growing watermelon plants in a Mars regolith simulant and to evaluate the possible beneficial effects of PGPB.

Watermelon seeds were treated with suspensions of PGPB previously confirmed to be metal-tolerant. The bacterial strains used were Pseudomonas chlororaphis (strain B0), Bacillus safensis (D0), and Bacillus thuringiensis (F4). The treatments included: F4 alone, a combination of D0 and F4, and a mixture of B0, D0, and F4. Sterile distilled water was used as a negative control. Following treatment and drying, the seeds were sown in soil and regolith simulant substrates, with 14 seeds per substrate type. Plants were grown in a growth box under a 14/10 h light/dark photoperiod at room temperature. After four weeks, the following growth parameters were measured: plant height, root length, number of leaves, total leaf area, fresh weight, total chlorophyll, and chlorophyll a and b content. The results were analyzed using a PERMANOVA test (Permutational multivariate analysis of variance) and pairwise permutation as a post-hoc test.

Plant growth was observed in both substrates, but growth in soil was generally more successful than in regolith. Statistically significant differences (p < 0.05) were found between plants grown in soil and regolith for all measured growth parameters, except for chlorophyll content, which remained similar regardless of the substrate. Regarding the effect of PGPB treatment on plants in regolith, the combination of strains B0+D0+F4 enabled germination of all seeds, compared to 78% germination in the untreated control. Based on mean values, treatment F4 had the most positive effect on chlorophyll content in regolith, while the combination D0+F4 showed the highest fresh weight. Although overall plant growth was influenced by substrate, treatment, and their interaction, no statistically significant differences were observed between the most effective treatments in regolith and the negative control.

This study demonstrated that watermelon can grow in a substrate simulating Martian regolith and that PGPB may enhance germination and improve certain growth parameters. Future research should incorporate additional stressors such as low temperatures and radiation to more accurately mimic Martian conditions.