Spatiotemporal variations affect uptake of inorganic and organic nitrogen by dominant plant species in an alpine wetland

Dominant plant species may coexist and maintain high productivity in alpine wetland through available nitrogen (N) niche differentiation over time and space. We tested the hypotheses that dominant plant species differ in uptake of inorganic and organic N and that such differences depend on soil depth and season. We conducted a short-term N-15-labeling experiment in an alpine wetland on the Tibetan Plateau. The experiment used a factorial design with three N forms (nitrate, ammonium and glycine), three soil depths (0-5, 5-10 and 10-15 cm), two seasons (May and July) and three dominant species (Carex muliensis, C. lasiocarpa and Potentilla anserina). All three species took up organic N (glycine), but showed different patterns over seasons and depths. N-15 uptake rate was higher in May than in July in C. muliensis and C. lasiocarpa, but lower in May than in July in P. anserina. C. muliensis took up more (NH4)-N-15 (+) and (NO3)-N-15 (-) than glycine-N-15 at all soil depths. C. lasiocarpa took up more glycine-N-15 than (NH4)-N-15 (+) or (NO3)-N-15 at 5-10 cm depth. P. anserina showed little difference in uptake at any soil depths. Dominant species in alpine wetland are able to take up both organic and inorganic N, but show different patterns depending on N form, soil depth, season and their interactions.