Hydrogels improve plant growth in Mars analog conditions

Abstract

Plants will be fundamental components of future human missions to Mars, and cultivation will probably suffer from the lack of optimal soils as well as of available liquid water. Additionally, the question as to whether Mars soils are suitable for plant cultivation is still open. Hydrogels are polymers able to absorb large quantity of water and have been shown to increase water retention in the soil, thus increasing plant establishment and growth. This work reports on the short-term assessment of plant growth in Mars soil analogs supplemented with hydrogels, in the constrained environment of a simulated life-on-Mars mission. Soil analogs consisted in sand and clay-rich material, sampled in the vicinity of the Mars Desert Research Station, a Mars analog facility surrounded by soils sharing similarities with mineralogical and chemical composition of Martian soils. Heights and dry biomass of Mentha spicata and seed germination of Raphanus sativus were monitored. Results revealed that clay-containing soil was the most unfavorable for the growth of control plants. The deleterious effects of Mars soil analogs on plant growth were potentiated under limited irrigation. By contrast, hydrogel amendment allowed for an overall improvement of plant endurance in Mars soil analogs, more pronounced under low watering conditions, leading to almost constant masses across conditions. Additionally, results point to an increase of seed germination rate in sand, which creates a dense medium with low water retention, that hydrogels might help loosening. The results suggest that Mars soil analogs can support the growth of plants in the tested conditions, and raise the hypothesis that in situ soils might be suitable for future exploration of Mars.