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

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. A short-term N-15 labeling experiment was conducted in the temperate grassland ecosystem of North China in July of 2013. Three N forms (NO3 (-) (,) NH4 (+) and glycine) labeled with N-15 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. Two hours after N-15 labeling, all three dominant plant species absorbed both organic and inorganic N, but different patterns were observed at two soil depths. Uptake of NO3 (-) was significantly higher at 0-5 cm than at 5-15 cm soil depth among all the dominant plant species. N-15 recovery by microbes was significantly higher than plants. However, N-15 recovery by plants showed different patterns over soil depths. 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.