LAUSR

Abstract Vegetation restoration affects soil N cycling, which in turn strongly affects ecosystem functions, such as plant productivity and N availability. The soil N availability is a major limiting factor for restoring vegetation in semiarid grasslands and affects landscape evolution. However, few studies have focused on how landscape evolution caused by vegetation restoration affects soil N availability and transformation in semiarid sandy grasslands. Here, we conducted a 5-year field experiment from 2015 to 2019 to evaluate the growth season (May–August) changes in soil inorganic N pools and net N transformation rates along a landscape evolution gradient caused by vegetation restoration: mobile dunes, semi-fixed dunes, fixed dunes, and dune grasslands. We examined the relationship between climate factors, vegetation characteristics, soil properties, and soil net N transformation rates in different landscape types through multivariate analyses. The landscape type, sampling time, interannual variation, and their interactive effects significantly affected the soil inorganic N pool and net N transformation rate. Soil nitrate N concentration accounted for 68% of the total inorganic N, and soil nitrification dominated the soil N transformation during landscape evolution. Redundancy analysis revealed that the changes in net N nitrification and mineralization rates during the growing season were closely correlated with climate factors, vegetation characteristics, and soil properties. Variation partitioning analysis showed that the soil net N transformation rate during the growing season was mainly affected by soil properties, whereas soil net N transformation in August for all years was mainly affected by climate factors. These results suggest that soil N availability and transformation during landscape evolution caused by vegetation restoration were co-determined by climatic factors, vegetation characteristics, and soil properties. Therefore, long-term field monitoring should be considered to improve our exploration of soil N transformation changes and their underlying mechanisms in semiarid grassland ecosystems.