Premium
Stimulated growth of Betula pubescens and Molinia caerulea on ombrotrophic bogs: role of high levels of atmospheric nitrogen deposition
Author(s) -
Tomassen Hilde B. M.,
Smolders Alfons J. P.,
Lamers Leon P. M.,
Roelofs Jan G. M.
Publication year - 2003
Publication title -
journal of ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.452
H-Index - 181
eISSN - 1365-2745
pISSN - 0022-0477
DOI - 10.1046/j.1365-2745.2003.00771.x
Subject(s) - ombrotrophic , sphagnum , betula pubescens , bog , ammonium , growing season , botany , nitrogen , chemistry , biology , zoology , peat , horticulture , agronomy , ecology , organic chemistry
Summary 1 In order to test whether the observed invasion of ombrotrophic bogs in the Netherlands by Molinia caerulea and Betula pubescens is the result of long‐term high nitrogen (N) loads, we conducted a 3‐year fertilization experiment with Sphagnum fallax turfs. Six different N treatments were applied ranging from 0 (control) to 4 g N m −2 year −1 . 2 During the experimental period, ammonium concentrations in the peat moisture remained very low due to high uptake rates by Sphagnum . Tissue N concentrations in S. fallax showed a linear response to the experimental N addition. Excess N was accumulated as N‐rich free amino acids such as arginine, asparagine and glutamine, especially at N addition rates of 0.25 g m −2 year −1 or higher, indicating N‐saturation. 3 Despite the high tissue N : P ratio (above 35), above‐ground biomass production by Molinia was still stimulated at N addition rates of 4 g m −2 year −1 , and foliar nutrient concentrations were unaffected compared to the control. In contrast to Molinia , Betula was unable to increase its above‐ground biomass. Foliar N concentrations in Betula were significantly higher at N addition rates of 4 g m −2 year −1 and excess N was stored in foliar arginine, making up 27% of the total N concentration. Evapotranspiration was increased at higher N addition rates due to stimulated total above‐ground biomass production of the vegetation. 4 N addition at the actual Dutch deposition rate of 4 g m −2 year −1 stimulated the growth of Molinia in this experiment, providing evidence that the observed dominance of Molinia on ombrotrophic bogs in the Netherlands is caused by high N deposition levels. Based on the observed changes in biomass production and tissue nutrient concentrations, we assume that a long‐term deposition of 0.5 g N m −2 year −1 , or higher, leads to undesirable changes in species composition and increased risk of desiccation.