Seasonal variation of net N mineralization under different biological soil crusts in Tengger Desert, North China

• Net N transformation rates were highest in August and lowest in January.
• The impacts of BSC are seasonally dependent and modified by environmental factors.
• BSC increased the net soil N transformation rates during the early growing season.
• BSC reduced the inorganic N content during peak growing season.

Biological soil crust (BSC) is a key biotic factor in desert areas and can significantly alter nutrient cycling. The interaction between seasonal climatic change and BSC can further modify nutrient cycling. Thus far, limited information has been provided regarding the effect of BSC on net soil nitrogen (N) transformation and their seasonal pattern in temperate desert areas. Therefore, we assessed the seasonal patterns of net soil N mineralization and nitrification in three microhabitats (moss-covered, cyanobacteria–lichen-covered, and bare soils) from October 2011 to September 2012 by using an intact soil core in situ incubation method. Seasonal variations in inorganic N pools, net N mineralization, and nitrification rates were observed. The seasonal patterns of net N transformation rates were greatly modified by soil temperature and moisture (highest in August and lowest in January). During non-growing season, net N immobilization was observed in the three microsites; a higher inorganic N content was observed in the moss-covered soil than in other soils. BSC increased the net soil N transformation rates during the early growing season but reduced the inorganic N content during the peak growing season. On the basis of these findings, we concluded that seasonal variation in climate significantly affected N transformation. The colonization and the development of BSC stimulated N cycling and storage in arid desert systems.