Effect of Pteropyrum aucheri Jaub. & Spach shrub on desert soil seed banks, application for restoring the medicinal plant Pergularia tomentosa

Pergularia tomentosa, a medicinally valuable species in arid regions, persists at critically low densities in recently years in Iran, demanding some conservation action. Its frequent coexistence with Pteropyrum aucheri, a shrub known to enhance its aboveground growth, prompted our investigation into P. aucheri's influence on soil seed bank (SSB) dynamics for potential restoration applications. Greenhouse germination of soil samples (beneath vs. outside shrub canopies) revealed 2,164 seedlings, with 68% (1,486) emerging from sub-canopy soils. P. aucheri significantly enhanced SSB density at 0-5 cm depth across functional groups: annuals (3,431 vs. 999), perennials (412 vs. 147), forbs (1,835 vs. 726), and grasses (2,048 vs. 424). Poaceae dominated the SSB composition (8 species). The complete absence of P. tomentosa germinants, despite its coexistence with P. aucheri, reveals a critical restoration constraint. This suggests that SSBs contributes minimally to P. tomentosa persistence and canopy-associated SSB enrichment doesn't benefit this target species. While P. aucheri creates favorable microsites for general SSB enrichment, its facilitation doesn't extend to P. tomentosa recruitment via seed banks. Restoration protocols must therefore combine shrub-retention (to maintain beneficial microhabitats) with active P. tomentosa reintroduction to ensure species recovery in degraded arid ecosystems. Active restoration such as direct seeding is essential.