Research on a microgravity-adapted controlled-release fertilizer for space plant cultivation and its application experiments in the space station

Abstract

This study developed a microgravity-adapted controlled-release fertilizer (CRF) for space plant cultivation and conducted application experiments aboard the Tiangong Space Station. First, through regular sampling and analysis, the nutrient uptake curve of lettuce under simulated microgravity was determined. Based on this curve, a CRF suitable for space cultivation was designed through adjustments in coating thickness and the incorporation of fertilizer particles with distinct release profiles. Subsequently, optimal application strategies were determined through simulated space environment experiments. The CRF was then applied in the Tiangong Space Station using the “Space Vegetable Garden” (SVG) facility to cultivate three lettuce varieties. Throughout the growth period, the substrate electrical conductivity was maintained within an optimal range of 150–300 mS/m. Under microgravity, the substrate nutrient distribution showed an upper-rich and lower-poor pattern, contrary to terrestrial conditions. The lettuce grown in space developed well, yielding nearly equivalent to ground-grown plants, with no observed symptoms of nutrient deficiency or salt stress. The expression levels of genes associated with nutrient deficiency (LsNLP, LsPHT1, LsWRKY) and salt tolerance (LsSOS1) were comparable to those in ground controls, indicating sufficient nutrient provision. Additionally, microgravity induced early bolting and flowering in lettuce. Analysis of returned samples revealed altered hormone distribution and up-regulated expression of flowering-related genes (LsFT, LsSOC1, LsLFY). This study enhances nutrient use efficiency and vegetable production capacity in space, advances understanding of microgravity effects on plant physiology, and provides technical support for developing controlled ecological life support systems (CELSS) for long-duration deep-space missions. Furthermore, it advances interdisciplinary research at the intersection of space science, agricultural engineering, and plant biology.