Symbiotic strategy of endophytic-rhizoidsphere microbiome with Takakia lepidozioides in alpine mountain of Tibetan Plateau

Plant-microbe symbiotic relationships are critical for ecosystem stability and functional maintenance, particularly in extreme alpine ecosystems. Takakia lepidozioides, one of the most primitive moss species in the world, has unclear mechanisms of interaction with microbes. This study focused on T. lepidozioides distributed along an altitudinal gradient (3800-4200 m) on Galongla Snow Mountain in southeastern Tibet. Through in situ field sampling, 16S rRNA and ITS amplicon sequencing were used to analyze microbial community structures in the rhizoidsphere and endophyte compartments, combined with metagenomic sequencing to examine functional characteristics. The study systematically investigated the T. lepidozioides-microbe symbiotic system and its cooperative adaptation mechanisms to alpine environments. Key findings are as follows:

(1) Significant differences existed between rhizoidsphere soil bacteria and endophytic bacteria in community composition, diversity, network structure, and assembly processes, with relatively smaller differences in fungi; altitude had no significant effect on symbiotic microbes (rhizoidsphere and endophyte), but they were influenced to some extent by physicochemical properties;

(2) Symbiotic microbes potentially assisted the host in basic element cycling, immunity, and antioxidant production, while supplementing indole-3-acetic acid synthesis pathways; symbiotic microbes relied on ABC transporters for N/S/P/Fe(III) transport but lacked transporters for sugars, organic acids/aromatics, metals/partial vitamins, amino acids, and defense-related proteins; endophytes contributed to host growth and stress resistance through enhanced amino acid metabolism, energy flow, terpenoid precursors, and carotenoid precursor synthesis compared to rhizoidsphere microbes;

(3) The symbiotic compartment contained many novel microbes (unclassifiable to species level by GTDB-Tk); endophytic metabolic modules were more diverse than those in the rhizoidsphere; endophytes exhibited pronounced community-function decoupling, with more frequent horizontal gene transfer events, consistent with weaker selection processes in endophytes.

In summary, this study revealed the roles of rhizoidsphere and endophytic microbes in supporting T. lepidozioidessurvival at the community and functional levels, providing the first comprehensive analysis of potential T. lepidozioides-microbe symbiotic relationships. These findings have significant implications for understanding early patterns of plant-microbe cooperative adaptation to extreme environments and for conserving endangered species.