Nitrogen translocation in Sphagnum mosses:: effects of atmospheric nitrogen deposition

Here, the hypothesis was tested that nitrogen (N) translocation from older to younger parts of Sphagnum decreases as N inputs from atmospheric deposition increase. Nitrogen translocation in Sphagnum mosses was compared in bogs with contrasting atmospheric N deposition (Adirondack-relatively high N deposition; Maine relatively low) and by following the movement of a (NH4)-N-15 (NO3)-N-15 tracer applied to plots of Sphagnum capillifolium over 2 yr. Annual N translocation ranged from 11% to > 80% in the lower and higher influx sites, respectively. Nitrogen translocation was an important process for the N budget of the Sphagnum mosses, contributing 0.5-11% of the annual N requirements. These results suggest that N translocation is as important as direct N retention from atmospheric deposition for the N budget of the mosses. Contrary to expectations, N translocation was greater in the high (Adirondack) than in the low (Maine) deposition sites. If N translocation is closely tied to water availability, the relative positions of the water tables in the sites over the course of the experiments might account for differences in N translocation among sites. The lower translocation (Maine) sites had lower water tables in the first year of the experiment and experienced a more severe drought in the second year than did the Adirondack sites.