The development of biological soil crusts shifts the drivers of soil multifunctionality in drylands

Biological soil crusts (BSCs) are essential components of drylands, yet the effects of their development on soil multifunctionality (SMF) and the drivers behind these effects remain unclear. We sampled 11 sites in Northwest China’s deserts, representing different successional stages of BSC development (i.e. cyanobacterial, lichen and moss crusts) as well as bare sand areas. We assessed the SMF of the crust layer and underlying soil at various depths (0–2, 2–5, 5–10, 10–20 cm) and also explored the influence of climatic factors (mean annual temperature, aridity, and solar radiation), crust characteristics (compressive strength, roughness, and thickness), and soil properties (pH, electrical conductivity, soil water content) on SMF across these layers. The presence of BSCs significantly enhanced soil nutritional status [soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), ammonia (NH₄⁺-N), nitrate (NO₃^–-N), and available phosphorus (AP)] throughout the 0–20 cm soil depth and increased SMF in the top 0–10 cm. These positive effects intensified with as BSCs progressed from cyanobacterial to lichen to moss stages, but decreased with soil depth. In the crust layer, SMF across all BSC types was positively influenced by our climatic factors. However, as BSCs developed, the negative influence of climatic factors (mainly solar radiation) and soil properties (mainly pH) on SMF decreased, while the positive influence of crust characteristics (mainly thickness) increased. The influence of climate, crust, and soil factors on SMF also decreased with increasing soil depth and varied by BSC type. Further, our findings demonstrate that the BSC development can buffer the negative effects of increased soil pH and solar radiation on SMF while enhancing the positive effects of crust properties, particularly thickness. This highlights the importance of preserving and promoting BSC development to enhance surface soil multifunctionality and mitigate the adverse effects of climate change on dryland ecosystem multifunctionality.