Sphagnum therefore appears to be highly efficient in using short N pulses (e.g. long-term N exposure) showed lower uptake rates than mosses from the pristine site, indicating an adaptive response. Uptake rates decreased drastically with increasing exposure times, which implies that many short-term N-uptake experiments in literature may well have overestimated long-term uptake rates and ecosystem retention. Ammonium was taken up 8 times faster than nitrate, whereas over 72 hours this was only 2 times. During the first 0.5 h, N-uptake followed saturation kinetics revealing a high affinity (K m 3.5–6.5 µM). Uptake rates for ammonium were higher than for nitrate, and N-binding at adsorption sites was negligible. We investigated the effects of N-concentration (1, 5, 10, 50, 100, 500 µM), N-form ( 15N - ammonium or nitrate) and exposure time (0.5, 2, 72 h) on uptake kinetics for Sphagnum magellanicum from a pristine bog in Patagonia (Argentina) and from a Dutch bog exposed to decades of N-pollution. The interacting effects of rain N concentration and exposure time on moss N-uptake rates are, however, poorly understood.
N-uptake kinetics of these mosses are therefore expected to play a key role in differential N availability, plant competition, and carbon sequestration in Sphagnum peatlands. Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N).
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