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Expansion of invasive species on ombrotrophic bogs: desiccation or high N deposition?
Author(s) -
Tomassen Hilde B. M.,
Smolders Alfons J. P.,
Limpens Juul,
Lamers Leon P. M.,
Roelofs Jan G. M.
Publication year - 2004
Publication title -
journal of applied ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.503
H-Index - 181
eISSN - 1365-2664
pISSN - 0021-8901
DOI - 10.1111/j.1365-2664.2004.00870.x
Subject(s) - ombrotrophic , peat , bog , botany , biology , betula pubescens , agronomy , sphagnum , ecology
Summary1 In many ombrotrophic bog areas the invasion of grass (e.g. Molinia caerulea ) and tree (e.g. Betula pubescens ) species has become a major problem. We investigated whether the invasion of such species is due to high atmospheric nitrogen (N) deposition by conducting a fertilization experiment. 2 The effects of experimentally increased N input on Molinia , Betula and Eriophorum vaginatum were studied in desiccated bog vegetation in Ireland, where there is relatively low background N deposition. Four different N treatments were applied for 3 years: 0 (control), 2, 4 and 8 g m −2 year −1 . 3 Ammonium and nitrate concentrations in the peat moisture increased at high N addition rates, leading to significantly higher carbon : nitrogen (C : N) and nitrogen : phosphorus (N : P) ratios in the top layer of the peat. The potential CO 2 production rate of the peat was not stimulated at high N addition rates due to severe acidification of the peat. 4 Despite high tissue N : P ratios (above 40), above‐ground biomass production by Molinia was stimulated at high N addition rates, and foliar nutrient concentrations were unaffected. In contrast to Molinia , Betula and Eriophorum were unable to increase their above‐ground biomass, probably due to P limitation. Regrowth of the lichen Cladonia portentosa was suppressed at high N addition rates. 5 Synthesis and applications. We conclude that the invasion of bogs by Molinia and Betula is likely to be less affected by desiccation than by increased N availability. Apparently, Molinia is well adapted to P‐limiting conditions, which may explain its success in regions with increased N deposition levels. The high availability of P in many Dutch bogs compared with Irish bogs, together with prolonged high N deposition levels, may explain the strong increase in both Molinia and Betula observed in the Netherlands. As long as N and P availabilities in Dutch bogs are too high to prevent invasion of Betula and/or Molinia , management measures stimulating growth of Sphagnum mosses could probably reduce the negative effects of high N deposition levels.