Hydrothermal conditions determine soil potential net N mineralization rates in arid and semi-arid grasslands

Soil net nitrogen (N) mineralization is a key biogeochemical process influencing plant available N and net primary productivity (NPP) in terrestrial ecosystems. However, the spatial variations and controlling factors of soil net N mineralization (RPNM) in arid and semi-arid grasslands are less studied and unclear. In this study, we investigated the soil RPNM by performing a laboratory incubation experiment. Soil samples were collected from 30 sites in three east-west transects on the Inner Mongolia Plateau (MP), Loess Plateau (LP), and Tibetan Plateau (TP) along a 3,200 km arid and semi-arid grassland gradient, with each transect containing three different grassland types (meadow steppe, typical steppe, and desert steppe, respectively). Results showed that the average RPNM values ranged from -0.37 to 1.29 mg N kg–1 d–1, with a significantly lower RPNM found in the desert steppe (0.08 ± 0.01 mg N kg–1 d–1) compared with those in the meadow steppe (0.30 ± 0.03 mg N kg–1 d–1) and in the ty...