Effects of altered precipitation patterns on soil nitrogen transformation in different landscape types during the growing season in northern China

Abstract

The soil nitrogen (N) cycle and transformation rate are susceptible to precipitation regime changes in semiarid sandy ecosystems, and they play important roles in both the soil fertility and in plant interactions. However, the response mechanisms of soil N transformation to changing precipitation regimes in semiarid ecosystems are still unclear. Thus, we conducted a three-year rainfall manipulation experiment along a landscape evolution gradient from fixed dunes to dune grasslands in a semiarid sandy region of northern China during the growing season (from May to September) between 2017 and 2019. The study included a contrast (P0: natural precipitation) and four treatments in which precipitation was decreased and increased by 60 % [P(−S) and P(+S)] between May and September and decreased and increased by 100 % [(P(−J) and P(+J)] between May and June. The soil nitrate nitrogen (NO3−-N) and inorganic N concentrations significantly increased under P(−S) and P(−J) (P < 0.05) in both fixed dunes and dune grasslands during the growing season. P(−S) and P(−J) significantly increased the soil net nitrification rate (Rn) and net N mineralization rate (Rm) only in July, with Rm significantly increasing with sampling months and years (P < 0.001). The structural equation model showed that Rn and Rm did not change with water availability variation, and an increase in Rm caused by the direct effects of increased precipitation was offset by its indirect effects mediated by reducing electrical conductivity and soil NO3−-N concentration while increasing soil water content and vegetation cover. Soil properties and vegetation characteristics were the main factors affecting soil N transformation during the growing season. Our findings are vital for understanding the seasonal patterns, cumulative N transformation, and possible climate change feedback of semiarid sandy land.