Abstract:

Biological soil crust （BSC）， known as "engineers of desert ecosystems，" are widely distributed in arid and semi-arid regions. Sand-fixing shrubs and BSC form mosaic patterns on the soil surface， and shrub litter significantly influences BSC development. However， how litter differences caused by shrub species and planting densities affect BSC colonization and growth remains poorly understood. In this study， we selected three sand-fixing shrub species—Calligonum mongolicum， Atraphaxis bracteata， and Hedysarum scoparium —planted at densities of 20， 35， and 50 plants/100 m² in the southeastern Tengger Desert. Coverage， thickness， and weight of litter and BSC attributes were measured， and the effects of litter properties on BSC growth were analyzed using multifactorialand regression analyses. The results showed that shrub species， planting density， and their interaction significantly influenced BSC biomass， extracellular polymeric substance content， and compressive strength. Additionally， shrub species significantly affected BSC thickness， while planting density notably influenced BSC coverage. Regression analysis found that， the relationships between BSC growth indicators and litter properties under different shrub species and densities were best fitted by quadratic function models， showing a pattern of first increasing and then gradually decreasing or decreasing changes. This study aims to conduct an in-depth investigation into this scientific issue， with the goal of providing scientific evidence and practical guidance for the coordinated restoration of sand-fixing shrubs and biological soil crusts in the southeastern edge of the Tengger Desert. At the same density， BSC development under C. mongolicum and H. scoparium was significantly better than under A. bracteata. Among planting densities， the BSC under three types of sand-fixing shrubs developed the best at 20 plants/100 m². The different types and planting densities of sand-fixing shrubs lead to differences in their litter properties， which in turn cause changes in the surface microenvironment and affect the colonization and development of BSC. In conclusion， for ecological restoration combining sand-fixing shrubs and BSC in the southeastern Tengger Desert， priority should be given to planting C. mongolicum and H. scoparium， followed by A. bracteata， with an optimal density of 20 plants/100 m². This study analyzed the optimized configuration mode of sand-fixing shrubs and BSC collaborative restoration of ecological environment in arid areas， providing scientific basis and practical guidance for wind and sand control and ecological restoration.

Key words: biological soil crust, sand-fixing shrubs, litter attributes, planting density