Response of soil N dynamics to land-use change and topographic position in a semiarid hilly grassland

Land-use changes through grazing exclusion (GE) or grassland afforestation (GA) are common restoring practices in semiarid ecosystems, but whether GE and GA exert similar or distinct effect on soil nitrogen (N) dynamics in certain ecosystem is still unclear, particularly in areas with complex terrain. Here, seasonal patterns of soil net N mineralization rates and mineral N contents were characterized in a hilly grassland on the Loess Plateau, China. A fenced grassland, an afforested shrubland and a grazing grassland (reference) with three topographic positions (the top, the north slope, and the south slope) were selected. Results showed that GE decreased soil net N mineralization rates but increased mineral N contents, while GA did not affect these metrics. Furthermore, topographic positions changed the effects of GE, with greater increase of soil total mineral N and nitrate N on the north slope than those on the top and the south slop. Soil layers also changed the effects of GE, with greater decrease in soil net N mineralization rates and greater increase in total mineral N and nitrate N contents at 0-10 cm than those at 10-20 cm. However, there was no difference among three topographic positions or between two soil layers under GA. These results demonstrated that GE was a better restoration practice than GA in respective of soil N dynamics.

Automated summary

Land-use changes through grazing exclusion (GE) or grassland afforestation (GA) can have different effects on soil nitrogen (N) dynamics in semiarid ecosystems. This study investigated the seasonal patterns of soil N mineralization rates and mineral N contents in a hilly grassland on the Loess Plateau, China. The results showed that GE decreased N mineralization rates but increased mineral N contents, while GA had no effect on these metrics. The effects of GE were influenced by topographic positions and soil layers, with greater increases in mineral N on the north slope and at 0-10 cm soil depth.