Nitrogen competition between three dominant plant species and microbes in a temperate grassland

Background and aims To test the hypothesis that dominant plant species could acquire different nitrogen (N) forms over a spatial scale and they also have the ability to compete for available N with microbes. Methods A short-term 15 N labeling experiment was conducted in the temperate grassland ecosystem of North China in July of 2013. Three N forms (NO 3 − , NH 4 + and glycine) labeled with 15 N were injected into the two soil depths (0–5 and 5–15 cm) surrounding each plant to explore N acquisition by plants and microbes. Three dominant plant species ( Artemisia frigida , Cleistogenes squarrosa and Artemisia capillaris ) were investigated. Results Two hours after 15 N labeling, all three dominant plant species absorbed both organic and inorganic N, but different patterns were observed at two soil depths. Uptake of NO 3 − was significantly higher at 0–5 cm than at 5–15 cm soil depth among all the dominant plant species. 15 N recovery by microbes was significantly higher than plants. However, 15 N recovery by plants showed different patterns over soil depths. Conclusions Dominant plant species in the temperate grassland have different patterns in acquisition of N added to soil in organic form and absorption of inorganic N, and microbes were more effectively than plants at competing for N in a short-term period.