Impacts of cyanobacteria-dominated biological soil crusts on seedling emergence and fate: an in situ experiment

Abstract Background and aims Biological soil crusts (BSCs) co-occur with vascular plants in many ecosystems. Nevertheless, little is known regarding the interaction among BSCs and vascular plants, and no standard methods exist aiming to evaluate BSC–plant interactions. While some reports emphasized the inhibition effect of BSCs on germination, others reported the opposite or did not find any differences between germination under crusted and non-crusted conditions. Contradictory findings were also reported regarding the BSC effects on vascular plants after germination, with some reports claiming that BSCs promote growth, while others claim the opposite. Methods By a seed addition experiment (using light and heavy seeds of three species belonging to the Fabaceae family) in an early-successional system in Germany, we tested in situ the emergence of seedlings under variable surface conditions (cyanobacterial crust, disturbed and removed crust), and quantified crust-plant interactions (survival, flowering) during and following seedling emergence. Results In comparison to an average of 8% of the light Lotus corniculatus and 20% of the light Ornithopus sativus that emerged through the cyanobacterial BSC, 76% of the heavy Glycine max emerged. Once emerged, the crust did not significantly affect the survival, growth, biomass, or flowering of G. max , whereas many of the seedlings from lightweight seeds dried up soon after emergence. The thickness of the cyanobacterial biocrust had no influence on Fabaceae emergence. Conclusion The cyanobacterial BSC acted as a filter that hindered the emergence of the lightweight seeds.