Soil conditioning for enhancing plant growth using biochar and hydrochar under microgravity

Cultivating plants in outer space is crucial for bioregenerative life support systems in human space exploration. This study aims to investigate the effects of soil conditioning with biochar and hydrochar on the growth and production of Malabar Spinach in microgravity conditions. Peanut shell biochar and wood hydrochar were applied at a 3% dosage by mass. Two gravity conditions were considered, including 1 g and microgravity simulated by a Random Positioning Machine (RPM). After an 18-day plant growth period, microgravity reduced the fresh biomass accumulation of Malabar Spinach by up to 71%. This reduction was attributed to inhibited leaf and root growth, which decreased light interception and nutrient uptake. In microgravity, biochar was more effective than hydrochar in enhancing plant production, mitigating the growth inhibition caused by microgravity. In the presence of biochar, microgravity significantly enhanced the biosynthesis of chlorophyll a and carotenoids by up to 36%. Furthermore, biochar and hydrochar treatments in microgravity conditions significantly increased the nutrient contents, such as K and P, in Malabar Spinach leaves. These findings indicate that biochar and hydrochar are promising soil conditioners for enhancing plant development in low-gravity conditions.