The colonization, succession and ecological processes of saxicolous moss crust in the Qinling Mountains

To advance the use of moss crust in restoring engineered slopes, this study characterized a Bryum plumosum -dominated crust in the Qinling Mountains. We analyzed changes in its microhabitats, physicochemical traits, and microbial communities during the succession to explain its success in colonizing bare rock. Our findings revealed that: (1) moss crust initiation was primarily localized to rock cracks and depressions, where superior water retention and dust accumulation established conducive microsites for propagule establishment. (2) Algal crust secretions were dominated by polycarboxylic acids and soluble sugars, enhancing weathering and moisture retention, while mosses released monocarboxylic acids and viscous carbohydrates that reinforced crust stability. Phytohormones common to both stages likely regulated moss development. (3) Bacterial dominance shifted from Cyanobacteria to Proteobacteria and Bacteroidetes, which correlated with higher nutrients, and metagenomic prediction indicated a functional transition toward lipid metabolism and signaling. The fungal community showed a relative decline in Ascomycota and a corresponding rise in unclassified taxa, paralleled by a trophic shift from symbiotrophy to pathotrophy and mixed strategies in later successional stages. (4) B. plumosum exhibited rapid water uptake and strong anchorage capacity, withstanding vertical and horizontal forces approximately 570 and 860 times its body weight, respectively, which ensures its effective establishment on rock surfaces. In conclusion, saxicolous moss crust formation is driven by synergistic microbe-plant interactions that mechanically and chemically reshape the rock substrate, progressively enhancing ecosystem stability. This study provides a theoretical framework for guiding species selection and restoration strategies for rocky slopes.