title: Sphagnum mosses--masters of efficient N-uptake while avoiding intoxication.
abstract: 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.
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, The Netherlands ; Centre for Energy and Environmental Studies, University of Groningen, Groningen, The Netherlands.
authors.forename: Christian
authors.initials: C
authors.lastname: Fritz
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors.forename: Leon P M
authors.initials: LP
authors.lastname: Lamers
authors.affiliation: Department of Environmental Science, GC University, Faisalabad, Pakistan ; Environment Department, University of York, York, United Kingdom.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Riaz
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors.forename: Leon J L
authors.initials: LJ
authors.lastname: van den Berg
authors.affiliation: Laboratory of Plant Physiology, University of Groningen, Groningen, The Netherlands.
authors.forename: Theo J T M
authors.initials: TJ
authors.lastname: Elzenga
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D064751:Ammonium Compounds / Q000378:metabolism; D007700:Kinetics; D016014:Linear Models; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D018547:Plant Stems / Q000187:drug effects / Q000378:metabolism; D044003:Sphagnopsida / Q000378:metabolism*; D013997:Time Factors
chemical_list: D064751:Ammonium Compounds; D009584:Nitrogen