Impacts of soil crusts on soil physicochemical characteristics in different rainfall zones of the arid and semi-arid desert regions of northern China

Soil crusts commonly form in arid and semi-arid desert regions once shifting sand dunes stabilize. The crusts affect soil properties such as texture and fertility. However, the role of crusts depends on the species composition, their physiological activity, and their stage of evolution, and varies with precipitation and season. In this study, the soil properties of physical and biological crusts in different rainfall zones of the arid and semi-arid desert regions of northern China were analyzed. More developed crusts had finer soil texture. The impact on chemical properties was greater in areas with higher precipitation. Contents of soil organic carbon (SOC), total nutrients, available N, and exchangeable ions did not vary among crust types in a hyperarid region. SOC, total N and P, and available N increased with crust development at 150–400 mm rainfall. Soil crusts increased available P during the initial stage of development. Crust development increased available K at 300–400 mm precipitation, but not at ≤250 mm precipitation. CaCO₃ changes were related to windblown dust and soil moisture in the crust. Electrical conductivity and total salinity varied in response to variation of soil nutrients and aeolian salt accumulation. The pH did not vary greatly between crust types and sites. Crust development was accompanied by soil alkalization. Ca²⁺ was more abundant than other cations. Crust development did not influence Cl⁻, but increased HCO₃ ⁻ and Na⁺. During crust development, SO₄ ²⁻ and K⁺ contents decreased, and Mg²⁺ increased, in regions with ≤250 mm precipitation. The opposite changes occurred at 300–400 mm precipitation.