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Sphagnum mosses--masters of efficient N-uptake while avoiding intoxication
Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N). N-uptake kinetics of these mosses are therefore expected to play a key role in differential N availability, plant competit...
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Published in: | PloS one 2014-01, Vol.9 (1), p.e79991 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N). 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. The interacting effects of rain N concentration and exposure time on moss N-uptake rates are, however, poorly understood. We investigated the effects of N-concentration (1, 5, 10, 50, 100, 500 µM), N-form ((15)N-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. Uptake rates for ammonium were higher than for nitrate, and N-binding at adsorption sites was negligible. During the first 0.5 h, N-uptake followed saturation kinetics revealing a high affinity (Km 3.5-6.5 µM). Ammonium was taken up 8 times faster than nitrate, whereas over 72 hours this was only 2 times. 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. Sphagnum from the polluted site (i.e. long-term N exposure) showed lower uptake rates than mosses from the pristine site, indicating an adaptive response. Sphagnum therefore appears to be highly efficient in using short N pulses (e.g. rainfall in pristine areas). This strategy has important ecological and evolutionary implications: at high N input rates, the risk of N-toxicity seems to be reduced by lower uptake rates of Sphagnum, at the expense of its long-term filter capacity and related competitive advantage over vascular plants. As shown by our conceptual model, interacting effects of N-deposition and climate change (changes in rainfall) will seriously alter the functioning of Sphagnum peatlands. |
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ISSN: | 1932-6203 1932-6203 |
DOI: | 10.1371/journal.pone.0079991 |