Asynchronous Recovery of Aboveground Vegetation and Depth-Stratified Soil Seed Banks with Changes in Community Assembly During Sandy Grassland Restoration in Hulunbuir, China

Assessments of sandy grassland restoration often rely on aboveground vegetation, but how germinable soil seed banks recover at different depths remains unclear. We examined a restoration chronosequence in the Hulunbuir Sandy Land, China, including unrestored sandy land, sites restored for 12, 14, 16, and 18 years, and natural grassland. Surveys of 300 sampling points in 2024 included vegetation inventories, seedling-emergence assays for the 0–2 and 2–10 cm soil layers, and soil physicochemical analyses. We applied partial Mantel tests and structural equation modeling and used null models to examine community assembly. Vegetation cover, species richness, and Shannon diversity generally rose with restoration, while soil total nitrogen and organic carbon increased and bulk density declined. Diversity was consistently greater in the surface seed bank and followed aboveground vegetation more closely; diversity in the deep seed bank remained low, suggesting slower recovery. Seed-bank density and the proportion of surface seeds were positively associated with soil chemical conditions and vegetation cover. Ecological drift dominated assembly, with homogeneous selection more apparent in early restoration and the deep layer. These findings suggest coupled but asynchronous recovery aboveground and belowground and support including seed banks at different depths and soil conditions in restoration assessments.