Spatio-temporal trends of nitrogen deposition and climate effects on Sphagnum productivity in European peatlands
Granath, G. ; Limpens, J. ; Posch, M. ; Mücher, S. ; Vries, W. de - \ 2014
Environmental Pollution 187 (2014). - ISSN 0269-7491 - p. 73 - 80.
carbon accumulation - n deposition - boreal mire - bogs - growth - vegetation - impact - mosses - forest - emissions
To quantify potential nitrogen (N) deposition impacts on peatland carbon (C) uptake, we explored temporal and spatial trends in N deposition and climate impacts on the production of the key peat forming functional group (Sphagnum mosses) across European peatlands for the period 1900–2050. Using a modelling approach we estimated that between 1900 and 1950 N deposition impacts remained limited irrespective of geographical position. Between 1950 and 2000 N deposition depressed production between 0 and 25% relative to 1900, particularly in temperate regions. Future scenarios indicate this trend will continue and become more pronounced with climate warming. At the European scale, the consequences for Sphagnum net C-uptake remained small relative to 1900 due to the low peatland cover in high-N areas. The predicted impacts of likely changes in N deposition on Sphagnum productivity appeared to be less than those of climate. Nevertheless, current critical loads for peatlands are likely to hold under a future climate.
How Does Tree Density Affect Water Loss of Peatlands? A Mesocosm Experiment
Limpens, J. ; Holmgren, M. ; Jacobs, C.M.J. ; Zee, S.E.A.T.M. van der; Karofeld, E. ; Berendse, F. - \ 2014
PLoS ONE 9 (2014)3. - ISSN 1932-6203 - 11 p.
sphagnum mosses - vascular plants - carbon-dioxide - climate-change - boreal mire - scots pine - vegetation - bogs - evapotranspiration - table
Raised bogs have accumulated more atmospheric carbon than any other terrestrial ecosystem on Earth. Climate-induced expansion of trees and shrubs may turn these ecosystems from net carbon sinks into sources when associated with reduced water tables. Increasing water loss through tree evapotranspiration could potentially deepen water tables, thus stimulating peat decomposition and carbon release. Bridging the gap between modelling and field studies, we conducted a three-year mesocosm experiment subjecting natural bog vegetation to three birch tree densities, and studied the changes in subsurface temperature, water balance components, leaf area index and vegetation composition. We found the deepest water table in mesocosms with low tree density. Mesocosms with high tree density remained wettest (i.e. highest water tables) whereas the control treatment without trees had intermediate water tables. These differences are attributed mostly to differences in evapotranspiration. Although our mesocosm results cannot be directly scaled up to ecosystem level, the systematic effect of tree density suggests that as bogs become colonized by trees, the effect of trees on ecosystem water loss changes with time, with tree transpiration effects of drying becoming increasingly offset by shading effects during the later phases of tree encroachment. These density-dependent effects of trees on water loss have important implications for the structure and functioning of peatbogs.
Persistent versus transient tree encroachment of temperate peat bogs: effects of climate warming and drought events
Heijmans, M.M.P.D. ; Knaap, Y.A.M. ; Holmgren, M. ; Limpens, J. - \ 2013
Global Change Biology 19 (2013)7. - ISSN 1354-1013 - p. 2240 - 2250.
raised bog - vegetation composition - plant-communities - ombrotrophic bogs - vascular plants - boreal mire - scots pine - sphagnum - ecosystems - responses
Peatlands store approximately 30% of global soil carbon, most in moss-dominated bogs. Future climatic changes, such as changes in precipitation patterns and warming, are expected to affect peat bog vegetation composition and thereby its long-term carbon sequestration capacity. Theoretical work suggests that an episode of rapid environmental change is more likely to trigger transitions to alternative ecosystem states than a gradual, but equally large, change in conditions. We used a dynamic vegetation model to explore the impacts of drought events and increased temperature on vegetation composition of temperate peat bogs. We analyzed the consequences of six patterns of summer drought events combined with five temperature scenarios to test whether an open peat bog dominated by moss (Sphagnum) could shift to a tree-dominated state. Unexpectedly, neither a gradual decrease in the amount of summer precipitation nor the occurrence of a number of extremely dry summers in a row could shift the moss-dominated peat bog permanently into a tree-dominated peat bog. The increase in tree biomass during drought events was unable to trigger positive feedbacks that keep the ecosystem in a tree-dominated state after a return to previous ‘normal’ rainfall conditions. In contrast, temperature increases from 1 °C onward already shifted peat bogs into tree-dominated ecosystems. In our simulations, drought events facilitated tree establishment, but temperature determined how much tree biomass could develop. Our results suggest that under current climatic conditions, peat bog vegetation is rather resilient to drought events, but very sensitive to temperature increases, indicating that future warming is likely to trigger persistent vegetation shifts. Keywords: alternative states, climate change, ecosystem model, extreme events, peatlands, pulse, rainfall, Sphagnum, temperature increase, vegetation shift
Resource contrast in patterned peatlands increases along a climatic gradient
Eppinga, M.B. ; Rietkerk, M. ; Belyea, L.R. ; Nilsson, M.B. ; Ruiter, P.C. de; Wassen, M.J. - \ 2010
Ecology 91 (2010). - ISSN 0012-9658 - p. 2344 - 2355.
boreal mire - ecosystems - phosphorus - vegetation - nitrogen - wetlands - bog - plants - temperature - mechanisms
Spatial patterning of ecosystems can be explained by several mechanisms. One approach to disentangling the influence of these mechanisms is to study a patterned ecosystem along a gradient of environmental conditions. This study focused on hummock–hollow patterning of peatlands. Previous models predicted that patterning in drainage-dominated peatlands is driven by a peat-accumulation mechanism, reflected by higher nutrient availability in hollows relative to hummocks. Alternatively, patterning in evapotranspiration (ET)-dominated peatlands may be driven by a nutrient-accumulation mechanism, reflected by reversed nutrient distribution, namely, higher nutrient availability in hummocks relative to hollows. Here, we tested these predictions by comparing nutrient distributions among patterned peatlands in maritime (Scotland), humid temperate (Sweden), and humid continental (Siberia) climates. The areas comprise a climatic gradient from very wet and drainage-dominated (Scotland) to less wet and ET-dominated (Siberia) peatlands. Nutrient distribution was quantified as resource contrast, a measure for hummock–hollow difference in nutrient availability. We tested the hypothesis that the climatic gradient shows a trend in the resource contrast; from negative (highest nutrient availability in hollows) in Scotland to positive (highest nutrient availability in hummocks) in Siberia. The resource contrasts as measured in vegetation indeed showed a trend along the climatic gradient: contrasts were negative to slightly positive in Scotland, positive in Sweden, and strongly positive in Siberia. This finding corroborates the main prediction of previous models. Our results, however, also provided indications for further model development. The low concentrations of nutrients in the water suggest that existing models could be improved by considering both the dissolved and adsorbed phase and explicit inclusion of both nutrient-uptake and nutrient-storage processes. Our study suggests that future climate change may affect the ecosystem functioning of patterned peatlands by altering the contribution of pattern-forming mechanisms to redistribution of water and nutrients within these systems
Field Simulation of Global Change: Transplanting Northern Bog Mesocosms Southward
Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Robroek, B.J.M. ; Berendse, F. - \ 2010
Ecosystems 13 (2010)5. - ISSN 1432-9840 - p. 712 - 726.
increased nitrogen deposition - increased n deposition - water-table depth - vascular plants - sphagnum mosses - litter quality - climate-change - boreal mire - peat bogs - mass-loss
A large proportion of northern peatlands consists of Sphagnum-dominated ombrotrophic bogs. In these bogs, peat mosses (Sphagnum) and vascular plants occur in an apparent stable equilibrium, thereby sustaining the carbon sink function of the bog ecosystem. How global warming and increased nitrogen (N) deposition will affect the species composition in bog vegetation is still unclear. We performed a transplantation experiment in which mesocosms with intact vegetation were transplanted southward from north Sweden to north-east Germany along a transect of four bog sites, in which both temperature and N deposition increased. In addition, we monitored undisturbed vegetation in control plots at the four sites of the latitudinal gradient. Four growing seasons after transplantation, ericaceous dwarf shrubs had become much more abundant when transplanted to the warmest site which also had highest N deposition. As a result ericoid aboveground biomass in the transplanted mesocosms increased most at the southernmost site, this site also had highest ericoid biomass in the undisturbed vegetation. The two dominant Sphagnum species showed opposing responses when transplanted southward; Sphagnum balticum height increment decreased, whereas S. fuscum height increment increased when transplanted southward. Sphagnum production did not differ significantly among the transplanted mesocosms, but was lowest in the southernmost control plots. The dwarf shrub expansion and increased N concentrations in plant tissues we observed, point in the direction of a positive feedback toward vascular plant-dominance suppressing peat-forming Sphagnum in the long term. However, our data also indicate that precipitation and phosphorus availability influence the competitive balance between Sphagnum, dwarf shrubs and graminoids.
Photosynthetic performance in Sphagnum transplanted along a latitudinal nitrogen deposition gradient
Granath, G. ; Strengbom, J. ; Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Berendse, F. ; Rydin, H. - \ 2009
Oecologia 159 (2009)4. - ISSN 0029-8549 - p. 705 - 715.
atmospheric nitrogen - n deposition - boreal mire - chlorophyll fluorescence - physiological-responses - parasitic fungus - water-content - growth - mosses - vegetation
Increased N deposition in Europe has affected mire ecosystems. However, knowledge on the physiological responses is poor. We measured photosynthetic responses to increasing N deposition in two peatmoss species (Sphagnum balticum and Sphagnum fuscum) from a 3-year, north-south transplant experiment in northern Europe, covering a latitudinal N deposition gradient ranging from 0.28 g N m(-2) year(-1) in the north, to 1.49 g N m(-2) year(-1) in the south. The maximum photosynthetic rate (NPmax) increased southwards, and was mainly explained by tissue N concentration, secondly by allocation of N to the photosynthesis, and to a lesser degree by modified photosystem II activity (variable fluorescence/maximum fluorescence yield). Although climatic factors may have contributed, these results were most likely attributable to an increase in N deposition southwards. For S. fuscum, photosynthetic rate continued to increase up to a deposition level of 1.49 g N m(-2) year(-1), but for S. balticum it seemed to level out at 1.14 g N m(-2) year(-1). The results for S. balticum suggested that transplants from different origin (with low or intermediate N deposition) respond differently to high N deposition. This indicates that Sphagnum species may be able to adapt or physiologically adjust to high N deposition. Our results also suggest that S. balticum might be more sensitive to N deposition than S. fuscum. Surprisingly, NPmax was not (S. balticum), or only weakly (S. fuscum) correlated with biomass production, indicating that production is to a great extent is governed by factors other than the photosynthetic capacity.
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.