Abstract:  Biological soil crusts (Biocrusts) are complex assemblages of lichens, bryophytes, cyanobacteria, fungi, and heterotrophic microbial organisms in the top few centimetres of desert soils. Biocrusts perform important ecological roles in the nitrogen cycle of desert ecosystems. In desert ecosystems, water sources are vital, and the seasonal melting snow in early spring resurrects biocrusts in the Gurbantunggut desert and begins nitrogen fixation. However, little is known about how biocrusts impact nitrifier distributions across the landscape, specifically ammonia oxidation archaea (AOA) and ammonia oxidation bacteria (AOB). In this study, we used fluorescent quantative PCR (qPCR) methods to characterize AOA and AOB amoA gene abundances at different soil depths (0–2, 2–5, 5–10 and 10–20 cm) in biocrust and biocrust-removal soils. Desert nitrification potential and soil physicochemical parameters were researched to understand biocrust impacts on the desert soil nitrogen cycle. The results showed that the AOA amoA gene abundance was remarkably larger than that of AOB across all soil samples. ANOVA results showed that biocrusts significantly affected AOA and AOB amoA gene abundance (P < 0.05) while PNR results indicated that biocrust removal significantly reduced soil nitrification potential (P < 0.001), which confirmed that biocrusts play an important role in regulating nitrogen transformation in the Gurbantunggut desert. A redundancy analysis confirmed that soil moisture and NH₄⁺-N were the key environmental factors affecting niche separation of AOA and AOB in desert soil.

Key words: the Gurbantunggut desert, biological soil crsut, ammonia-oxidizing microbes, desert soil, nitrogen transformation