Abstract: We explored the mineralization potential of soil organic carbon (SOC) between two land use types, shrubland and cropland, in the southern edge of the desert-oasis transition zone in hyper-arid area of the Taklamakan Desert, and analyzed the response mechanism to nitrogen (N) addition. Adjacent uncultivated desert land was used as a control. NH₄Cl was used as the N source. The SOC mineralization rate and cumulative SOC mineralization were measured in an incubation experiment in the laboratory. The regulatory factors of SOC mineralization including the microbial community composition and enzyme activities related to carbon and N cycling were explored. The results showed that land use types had a significant impact on the cumulative mineralization of SOC. The cumulative mineralization of SOC in cropland and shrubland were significantly higher than those in uncultivated desert land (P<0.05). The mineralization rate of SOC peaked on the 1st or 3rd day, and then gradually decreased with the extension of incubation time. The cumulative mineralization of SOC was significantly negatively correlated with soil dissolved organic N, ammonium, and nitrate, but positively correlated with pH (P<0.05). Redundancy analysis showed that 95.02% of the variation of SOC mineralization was explained by enzyme activity and microbial community composition, and fungi to bacteria ratio. Gram-positive bacteria and actinomyces abundances exerted the greatest impact on SOC mineralization. Nitrogen addition delayed the occurrence time of the maximum of soil mineralization rate in shrublands and uncultivated desert lands, but did not affect soil microbial community composition and SOC cumulative mineralization. These findings indicate that the reclamation of desert lands into shrublands and croplands can increase SOC mineralization, with nutrient availability playing an important role in this process.

Key words: soil organic carbon mineralization, land use type, nitrogen addition, enzyme activity, microbial community composition