Abstract: Seasonal variations of soil inorganic nitrogen pool and net transformation rates under cyanobacteria-lichen-covered soil and in the bare soil were observed by using close-top tube incubation method in a natural vegetation area of Shapotou, southeastern fringe of the Tengger Desert. Results showed that obvious seasonal dynamics were found in soil labile nitrogen pools and net nitrogen mineralization rate, in which the order were: peak growing season > early growing season. In addition, soil labile nitrogen content and net nitrogen transformation rates were highest in July and August; the soil labile nitrogen content and net nitrogen transformation rates were significantly different between cyanobacteria-lichen-covered soil and bare soil. In early growing season, no obvious differences were found between the two sample soils and soil transformation process was primarily controlled by temperature. In peak growing season, the regularity for soil labile nitrogen and net nitrification rate was bare soil > cyanobacteria-lichen-covered soil, furthermore, moisture and temperature are respectively key environmental factors that affected soil nitrification and mineralization process. Our results indicated that the existence of cyanobacteria-lichens seems to be able to reduce the N losses by inhibiting soil nitrification process and establish a mechanism of soil nutrient preservation.

Key words: biological soil crusts-soil system, inorganic nitrogen pool, net nitrogen mineralization rate