Abstract: To explore the dynamics of nitrogenase activity and their microbial mechanisms in different types of biological soil crusts (BSCs), we compared the nitrogenase activities of different BSCs stages (algal crusts, lichen crusts, and moss crusts) and explored the microbial mechanisms regulating nitrogenase activity in the aeolian sandy area of northwestern Shanxi Province. The results showed that nitrogenase activity significantly increased with BSCs development, with a rate of 1.45, 1.89, and 2.21 μmol C₂H₄·g^-1·h^-1 in algal crusts, lichen crusts, and moss crusts, respectively. The contents of total organic carbon, total nitrogen (TN), nitrate nitrogen, available phosphorus, and available potassium exhibited significant increasing trends with BSCs development, reaching peak values at the moss crust stage. Nostoc and Azospirillum were the dominant genera in the diazotrophic communities of BSCs. TN and mean annual precipitation (MAP) were identified as the key factors influencing diazotrophic communities. In terms of biological factors, the nitrogenase activity in BSCs was mainly regulated by Rhodospirillales and Rhizobiales. Rhodospirillales exerted a positive effect, while Rhizobiales had a negative effect. Regarding abiotic factors, nitrogenase activity was primarily indirectly regulated by pH, TN and MAP.

Key words: biological soil crusts, nitrogenase activity, nifH gene, loess sandy region