Boreal bog plants: nitrogen sources and uptake of recently deposited nitrogen

摘要

The main goals of this study were to determine the δ~(15)N signature of quantitatively important boreal bog plants as basis for discussing their N sources, and to assess the effects of five different 3 year N treatments (i.e. 0, 5, 10, 20 and 40 kg N ha~(-1) year~(-1)) on the bog plants and surface peat at different depths (i.e. 0, 5, 10, 20 and 40 cm) by using ~(15)N as tracer. Plants and peat were analyzed for N concentration, ~(15)N natural abundance and ~(15)N at.%. From the results we draw three main conclusions: First, the relative importance of different N sources is species-specific among bog plants. Second, an annual addition of 5 kg N ha~(-1) year~(-1) was sufficient to significantly increase the N concentration in Sphagnum mosses, liverworts and shallow rooted vascular plants, and an annual addition of 40 kg N ha~(-1) year~(-1) during 3 years was not sufficient to increase the N concentration in deep rooted plants, although the ~(15)N content increased continuously, indicating a possible longer term effect. Third, an annual addition of 40 kg N ha~(-1) year~(-1) during 3 years increased the N content in surface peat at depths of 5 and 10 cm, but not at depths of 20 and 40 cm, indicating the capacity of the living Sphagnum mosses and the surface peat to take up deposited N, and thereby function as a filter.