Wheat rhizospheric microbial network's consistent modular pattern in improved lunar soil simulant accompanied with fungal withdrawal

Crewed base is the undoubted trend of lunar exploration. Human long-term residence needs Bioregenerative Life Support System (BLSS) where plant cultivation serves as the core functional unit. Given the difficulty of Earth-Moon transport, lunar soil has the potential as plant cultivation substrates in situ, yet its cultivability needs to be improved to meet the life-support needs. Imitating the Earth soil's bioweathering process, we fermented lunar soil simulant with BLSS's daily product—the solid waste (fermented from highly lignocellulosic organic waste) as an improvement, and conducted wheat whole-life-span (“from seed to seed”) cultivation experiment. The improvement of the lunar soil simulant was evaluated by wheat growth and production, while plant-substrate interactions were elucidated via rhizospheric microbial community's structure and function. Results showed that the wheat's shoot fresh weight and seed production were both significantly improved, but trace-amount (1/1000 w/w) solid waste addition achieved the best. Rhizospheric microbial molecular ecological networks (pMENs) showed that a functional module mainly composed of Proteobacteria (“Module P″) positively correlated with wheat growth, while another functional module mainly composed of lignocellulolytic Bacteroidota and Firmicutes (“Module BF”) negatively correlated with wheat growth. Such a consistent two-major-module pattern across all networks suggests a universal pattern for lunar soil simulant wheat cultivation's rhizospheric microbial communities. Moreover, rhizospheric phytopathogenic fungal genus' abundance positively correlated the addition amount of solid waste, and fungi showed a gradual withdrawal from the networks during the cultivation, seeming like a community succession triggered by both wheat rhizospheric phytoprobiotic recruitment (competitive) and solid waste depletion (nutritional). This study proves the feasibility of using BLSS's daily waste to improve lunar soil simulant's plant cultivability, and reveals the interaction pattern of its rhizospheric microbial communities. However, the lignocellulosic solid waste still contains microbial degraders which threaten the plant's lignocellulosic cell wall, indicating its merely semi-decomposed nature and thus calling for improved post-treatments to provide a more decomposed cultivation environment with healthier rhizospheric microbial community for future lunar BLSS plants.