Abstract

As humanity ventures into extraterrestrial agriculture and advances controlled-environment farming, understanding how plants integrate directional growth cues under altered abiotic conditions is essential. This study investigated the responses of Allium fistulosum to hydrotropism, magnetotropism, and gravitropism across a matrix of controlled environmental treatments. A custom-built three-dimensional clinostat was used to simulate microgravity at 0.02 g, 0.10 g, and 0.25 g. Plants were cultivated under both homogeneous and heterogeneous water distributions and exposed to static magnetic fields (SMFs) exerting pull forces of 0.10, 0.20, 0.50, and 1.00 kg. Each growth condition was designed to isolate specific combinations of directional cues, with customized soil chambers controlling the spatial distribution of water and magnetic exposure. Over a defined growth period, shoot and root architecture, fresh and dry biomass, and chlorophyll a and b concentrations were recorded. Statistical significance of treatment effects was evaluated using analysis of variance.

Microgravity increased shoot elongation but reduced total biomass and pigment levels, indicating disrupted statolith sedimentation and plastid development. SMFs enhanced root count, biomass, and chlorophyll content, likely through changes in ion

flux, reactive oxygen species signaling, and meristem activity. Water gradients triggered hydropatterning, with lateral roots elongating toward moisture-rich zones, possibly regulated by abscisic acid (ABA). Microgravity also impaired auxin redistribution, resulting in disoriented root growth and fewer secondary roots.

These findings demonstrate the integration of tropic stimuli in altered environments and reveal how environmental physics modulates plant development via hormonal, cellular, and biochemical pathways, offering a foundation for future research in extraterrestrial agriculture and climate-adaptive crop design.