Decreased summer water table depth affects peatland vegetation
Breeuwer, A.J.G. ; Robroek, B.J.M. ; Limpens, J. ; Heijmans, M.M.P.D. ; Schouten, M.G.C. ; Berendse, F. - \ 2009
Basic and Applied Ecology 10 (2009)4. - ISSN 1439-1791 - p. 330 - 339.
sphagnum mosses - nitrogen deposition - vascular plants - interspecific competition - decomposition rates - bog vegetation - n deposition - community - level - co2
Climate change can be expected to increase the frequency of summer droughts and associated low water tables in ombrotrophic peatlands. We studied the effects of periodic water table drawdown in a mesocosm experiment. Mesocosms were collected in Southern Sweden, and subsequently brought to an experimental field in the Netherlands. Two water table treatments were applied: one with constant water tables at 5 cm below the moss surface, and one in which the water table was allowed to drop, resulting in water tables fluctuating between 5 and 21 cm below the moss surface. Sphagnum growth, as well as Sphagnum and vascular plant abundance, were assessed for years. Our results show that the abundance of graminoid species increased most in the constant water table treatment. In contrast, ericoid species cover increased when water tables were allowed to fluctuate. Furthermore, Sphagnum cuspidatum production decreased with fluctuating summer water tables, while Sphagnum magellanicum responded oppositely. From these results we conclude that increased occurrence of periods with low water tables may bring about a shift in dominant Sphagnum species as well as a shift from graminoid to ericoid vascular plant cover, resembling the shift from hollow to lawn or hummock vegetation. The difference in response within functional groups (vascular plants, Sphagnum) may add to the resilience of the ecosystem.
Nitrogen content and d15N signature of ombrotrophic Sphagnum plants in Europe: to what extent is the increasing atmospheric N deposition altering the N-status of nutrient-poor mires?
Bragazza, L. ; Limpens, J. ; Gerdol, R. ; Grosvernier, P. ; Hajèk, M. ; Hajkova, P. ; Lacumin, P. ; Kutnar, L. ; Rydin, H. ; Tahvanainen, T. - \ 2005
Global Change Biology 11 (2005)1. - ISSN 1354-1013 - p. 106 - 114.
n-15 natural-abundance - atmospheric deposition - isotope composition - n-15/n-14 ratios - vascular plants - wet deposition - bog vegetation - carbon-dioxide - nitrate - growth
Alteration of the global nitrogen (N) cycle because of human-enhanced N fixation is a major concern particularly for those ecosystems that are nutrient poor by nature. Because Sphagnum-dominated mires are exclusively fed by wet and dry atmospheric deposition, they are assumed to be very sensitive to increased atmospheric N input. We assessed the consequences of increased atmospheric N deposition on total N concentration, N retention ability, and 15N isotopic signature of Sphagnum plants collected in 16 ombrotrophic mires across 11 European countries. The mires spanned a gradient of atmospheric N deposition from about 0.1 up to about 2 g m2 yr1. Mean N concentration in Sphagnum capitula was about 6 mg g1 in less polluted mires and about 13 mg g1 in highly N-polluted mires. The relative difference in N concentration between capitulum and stem decreased with increasing atmospheric N deposition, suggesting a possible metabolic mechanism that reduces excessive N accumulation in the capitulum. Sphagnum plants showed lower rates of N absorption under increasing atmospheric N deposition, indicating N saturation in Sphagnum tissues. The latter probably is related to a shift from N-limited conditions to limitation by other nutrients. The capacity of the Sphagnum layer to filter atmospheric N deposition decreased exponentially along the depositional gradient resulting in enrichment of the mire pore water with inorganic N forms (i.e., NO3+NH4+). Sphagnum plants had 15N signatures ranging from about 8 to about 3. The isotopic signatures were rather related to the ratio of reduced to oxidized N forms in atmospheric deposition than to total amount of atmospheric N deposition, indicating that 15N signature of Sphagnum plants can be used as an integrated measure of 15N signature of atmospheric precipitation. Indeed, mires located in areas characterized by greater emissions of NH3 (i.e., mainly affected by agricultural activities) had Sphagnum plants with a lower 15N signature compared with mires located in areas dominated by NOx emissions (i.e., mainly affected by industrial activities).
Nutritional constraints in ombrotrophic Sphagnum plants under increasing atmospheric nitrogen deposition in Europe
Bragazza, L. ; Tahvanainen, T. ; Kutnar, L. ; Rydin, H. ; Limpens, J. ; Hajek, M. ; Grosvernier, P. ; Hansen, I. ; Lacumin, P. ; Gerdol, R. - \ 2004
New Phytologist 163 (2004)3. - ISSN 0028-646X - p. 609 - 616.
nutrient limitation - n-deposition - bog vegetation - raised bogs - growth - co2 - water - wet - acidification - accumulation
We studied the effects of increasing levels of atmospheric nitrogen (N) deposition on nutrient limitation of ombrotrophic Sphagnum plants. • Fifteen mires in 11 European countries were selected across a natural gradient of bulk atmospheric N deposition from 0.1 to 2 g/m2 year-1. Nutritional constraints were assessed based on nutrient ratios of N, phosphorus (P), and potassium (K) in Sphagnum plants collected in hummocks (i.e. relatively drier microhabitats) and in lawns (i.e. relatively wetter microhabitats). • Nutrient ratios in Sphagnum plants increased steeply at low atmospheric N input, but above a threshold of N deposition of c. 1 g/m2 year-1 the N : P and N : K ratios tended to saturation. Increasing atmospheric N deposition was also accompanied by a reduced retention of Ca and Mg in Sphagnum plants and a decreased stem volumetric density in hummock Sphagnum plants. • We suggest a critical load of N deposition in Europe of 1 g/m2 year-1 above which Sphagnum plants change from being N-limited to be K + P colimited, at N : P > 30 and N : K > 3.
Effects of elevated CO2 and N deposition on CH4 emissions from European mires
Silvola, J. ; Saarnio, S. ; Foot, J. ; Sundh, I. ; Greenup, A. ; Heijmans, M.M.P.D. ; Ekberg, A. ; Mitchell, E.P. ; Breemen, N. van - \ 2003
Global Biogeochemical Cycles 17 (2003)2 - 1068. - ISSN 0886-6236 - p. 37 - 1-37-12.
atmospheric carbon-dioxide - methane emissions - boreal mire - raised co2 - northern peatlands - water-table - nitrogen deposition - bog vegetation - forest soils - temperature
 Methane fluxes were measured at five sites representing oligotrophic peatlands along a European transect. Five study plots were subjected to elevated CO2 concentration (560 ppm), and five plots to NH4NO3 (3 or 5 g N yr(-1)). The CH4 emissions from the control plots correlated in most cases with the soil temperatures. The depth of the water table, the pH, and the DOC, N and SO4 concentrations were only weakly correlated with the CH4 emissions. The elevated CO2 treatment gave nonsignificantly higher CH4 emissions at three sites and lower at two sites. The N treatment resulted in higher methane emissions at three sites (nonsignificant). At one site, the CH4 fluxes of the N-treatment plots were significantly lower than those of the control plots. These results were not in agreement with our hypotheses, nor with the results obtained in some earlier studies. However, the results are consistent with the results of the vegetation analyses, which showed no significant treatment effects on species relationships or biomass production.