Micro-morphology, ultrastructure and chemical composition changes of Bryum argenteum from a desert biological soil crust following one-year desiccation

Biological soil crusts dominated by mosses are commonly found in arid and semiarid areas, where mosses spend large parts of their time in a state of intense desiccation. The effective recovery of moss crusts after long-term desiccation is vital for their survival. In this study, we analyzed the changes in micromorphology, ultrastructure and chemical composition in Bryum argenteum samples desiccated for 1 week or 1 year. We used non-destructive and anhydrous methods of analysis, including scanning electron microscopy, transmission electron microscopy and Fourier transform infrared analysis. After long-term desiccation (1 year), B. argenteum samples showed a rapid recovery of F-V/F-M in the light after rehydration. For the 1-year desiccated samples, the thallus remained intact but shrunken. Within the thallus, cell arrangement was disorderly, cell shapes were irregular, and cell walls were thinner. Inside cells, chloroplasts remained intact, but some thylakoids were degraded. In terms of the major cellular components, the lipid and carbohydrate contents increased, the numbers of alpha helixes and beta sheets in protein secondary structures increased, while the number of turn structures in proteins decreased. The changes in protein secondary structure appear to be an important factor in the tolerance of B. argenteum to long-term desiccation. The recovery mechanisms that function after rehydration include processes for the repair of protein conformation and the re-synthesis of thylakoids.