Preliminary Results of the ISS Plant Habitat PH-07 Experiment Studying Substrate Moisture Impacts on Lettuce Plant and Microbiome Development

Providing crops adequate root zone moisture and aeration in microgravity is challenging due to the behavior of fluids and gasses during spaceflight. Chronic excess or insufficient moisture, or intermittent watering leading to wilting, change plant growth, and may impact crop nutrition, food safety, and microbiomes. PH-07 applied controlled water treatments to assess and quantify changes in growth and the microbiome of ‘Outredgeous’ red romaine lettuce, grown in the Advanced Plant Habitat (APH) on ISS compared to a ground control. Three replicates were performed with 3 plants subjected to one of four moisture treatments: control conditions holding ~52% volumetric moisture content, flood conditions holding ~2% below total saturation, drought conditions reaching ~35% moisture and providing sufficient water for survival, and wilt conditions operated as controls for 14 days, then withholding water until plants wilted for 24 hours, then restoring water to 52% and repeating. Flight and ground operations generally went as planned, though seed sanitization led to slowed germination and growth in later flight tests and to germination challenges in the initial ground control. These issues were resolved, and ground controls were completed successfully. Postflight analyses will include culturable microbial assessment for food safety, nutritional assessment, microbiome assessment of returned shoots and extracted roots, proteomics, and image analysis. Control plant growth generally appeared excellent, with flood, wilt, and drought-treated crops showing impaired growth. Analyses are underway, with initial findings indicating low culturable microbial levels and no pathogens. PH-07 will provide insight on short and long-term impacts of water stress for space crop production. This work was funded by NASA Space Biology.