ASHS 2025 Conference

Sustainable fresh vegetable crop production using lunar regolith as a growth media is critical for establishing large-scale space farming on the lunar surface. While lunar regolith contains essential mineral nutrients, it lacks organic carbon and nitrogen, which limits mineral bioavailability and nutrient-holding capacity. Tetradesmus deserticola is a terrestrial, photosynthetic algae that self-propagate in minimal media using light and carbon dioxide. It contributes organic matter to marginal soils through photosynthesis and has been used as biostimulant. The objective of this research was to evaluate the effects of T. deserticola inoculation on the growth, physiological, and morphological responses of lettuce (Lactuca sativa) plants at ammonium nitrate rates of 0, 1, and 2 mM, and 15N–3.9P–10K controlled-release fertilizer (CRF) at rates from 0 to 8.4 g·L-1 in a containerized silica sand media. Lettuce seeds were sown in the containerized media and inoculated with dried T. deserticola. After seed emergence, plants were irrigated with nitrogen-free Hoagland’s solution supplemented with ammonium nitrate or top-dressed with CRF at rates from 0 to 8.4 g·L-1. Electrical conductivity (EC), pH, and nitrate-nitrogen concentrations in leachate were recorded weekly. Gas exchange rates were measured, and plants were harvested 59 days after sowing to assess growth and morphological responses. Nitrate-nitrogen concentration and EC in leachate increased with increasing levels of ammonium nitrate in the Hoagland’s solution and CRF rates. In addition, the plant growth index and relative chlorophyll content of leaves was enhanced with the increase of ammonium nitrate levels and CRF application rate. Compared with non-inoculated plants, lettuce inoculated with T. deserticola showed higher plant growth index and relative leaf chlorophyll content when receiving nitrogen-free Hoagland’s solutions with 0, 1, and 2 mM of ammonium nitrate. However, the inoculation of T. deserticola did not increase plant growth index and relative chlorophyll content for plants treated with CRF. The T. deserticola inoculation enhanced growth and physiology of the Romaine lettuce at ammonium nitrate levels ranging from 0 to 2 mM. However, T. deserticola did not affect plant development when the plants were treated with CRF. Under the conditions of this study, the effects of T. deserticola inoculation on plant growth differed between fertilizer management.