Patch size indirectly influences the distribution characteristics of phosphorus fractions in temperate desert moss crust soils

Biological soil crusts (BSCs) are widely developed in desert areas. As an advanced stage of BSCs development, moss crusts are usually distributed in patches and have a profound impact on the phosphorus cycling process of the surface soil in deserts. However, the impact of different patch sizes on soil phosphorus cycling and phosphorus fractions, as well as the consistency of responses between the crust layer and the lower 0-5 cm of soil, remains unclear. The results examined moss crusts of varying patch sizes in the Gurbantunggut Desert. Phosphorus fractions from the crust layer and the lower 0-5 cm of soil were extracted through continuous leaching, and the phosphorus cycle-related enzyme activities were determined. The results indicated that the moss crust patches were predominantly composed of stable HCl-Pi, constituting 79% of the total phosphorus. NaHCO3-Po in the crust layer increased with patch size, whereas NaOH-Pi, medium labile phosphorus (med-labile P), and the activities of alkaline phosphatase and phosphodiesterase decreased with patch size in the lower 0-5 cm soil. Compared to the lower 0-5 cm soil, the crust layer exhibited lower Resin-P, NaHCO3-Pi, and total labile phosphorus (labile P), but higher med-labile P and stable phosphorus (stable P). The disparity in the labile P between the crust layer and the lower 0-5 cm of soil decreased with the increasing patch size. SEM revealed that the patch size affected the soil phosphorus fractions indirectly by influencing the soil nutrients and the metal elements (Fe, Ca). In summary, the presence of moss crust patches reduced the total soil phosphorus effectiveness but increased the soil organic phosphorus accumulation. This will provide a certain basis for improving the soil phosphorus nutrient status of desert ecosystems and the restoration of desert ecosystems in the future.