Biocrust and sand burial together promote annual herb community assembly in an arid sandy desert area

Background Annual herbs are crucial components of sandy ecosystems and their community assembly in arid sandy dunes is an intuitive indicator of a degraded ecosystem’s successful restoration. In sandy areas, biocrust and sand burial often co-occur, given the higher diversity and biomass of annual herbs where both factors co-occur than where either does alone. Yet our knowledge of the underlying mechanism is limited. Methods A field survey was conducted to verify that the presence of biocrust and sand burial jointly promoted the assembly of herbs. And then controlled simulating experiments were conducted to investigate the individual and collective effects of three biocrusts (bare sand (control), cyanobacterial crust, and moss crust) and three depths (0 (control), 2.5, and 5 mm) of sand burial upon germination, growth of three annual herbs as well as the soil water and nutrition status in a revegetated area of the Tengger Desert. Results Biocrust inhibited seed germination of the three annual herbs, but promoted their seedling growth. However, sand burial disrupted the inhibitory influence upon seed germination and strengthened the positive effects of biocrust on seedling growth of all species, by improving the availability of water and nutrients in upper soil. Conclusion Mutual complementary effects of biocrust and sand burial promote the establishment, and overall recruitment success of annual herbs. This finding emphasizes the importance of buried disturbance of biocrust in plant community assembly processes, providing an approach to disentangle relationships between biocrust and vascular plants, and a new technique suggestion for ecological restoration in arid sandy areas.