Abstract: The phoD-harboring bacteria play a crucial role in regulating organic phosphorus (Po) mineralization in soil. Although previous studies have demonstrated that phoD-harboring bacteria mediate P turnover under nitrogen (N) deposition across various ecosystems, it remains unclear how biocrusts regulate phoD abundance and drive P cycling in desert ecosystems. Here, we used a 13-yr field experiment in the Gurbantunggut Desert to disentangle the effects of long-term N deposition on phoD-mediated P cycling across moss and lichen biocrusts under contrasting seasonal conditions. The results reveal that moss crusts had significantly higher concentrations of labile inorganic phosphorus (Pi), labile Po, and available P compared to lichen crusts. Long-term N deposition resulted in a significant accumulation of available P, closely correlated with the release of calcium-bound P through soil acidification, particularly during the growing season. Low N deposition enhanced Po mineralization by elevating alkaline phosphatase (ALP) activity, while high N deposition suppressed phoD gene abundance and ALP activity, thus weakening the Po mineralization process. Additionally, high N deposition significantly reduced the α-diversity of phoD-harboring bacterial communities and reshaped community structure, increasing the relative abundance of Actinomycetota and decreasing that of Pseudomonadota. In conclusion, long-term N deposition regulates P bioavailability in desert biocrusts through soil acidification processes, ALP activity, and microbial communities, with these effects modulated by crust type and season. This study offers new insights into how N impacts P cycling in desert ecosystems and emphasizes the importance of managing N inputs to maintain nutrient balance and stability.

Key words: N deposition, P bioavailability, phoD-harboring bacteria, biocrusts, dryland