Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Environmental and taxonomic controls of carbon and oxygen stable isotope composition in Sphagnum across broad climatic and geographic ranges
    Granath, Gustaf ; Rydin, Håkan ; Baltzer, Jennifer L. ; Bengtsson, Fia ; Boncek, Nicholas ; Bragazza, Luca ; Bu, Zhao Jun ; Caporn, Simon J.M. ; Dorrepaal, Ellen ; Galanina, Olga ; GaÅka, Mariusz ; Ganeva, Anna ; Gillikin, David P. ; Goia, Irina ; Goncharova, Nadezhda ; Hájek, Michal ; Haraguchi, Akira ; Harris, Lorna I. ; Humphreys, Elyn ; Jiroušek, Martin ; KajukaÅo, Katarzyna ; Karofeld, Edgar ; Koronatova, Natalia G. ; Kosykh, Natalia P. ; Lamentowicz, Mariusz ; Lapshina, Elena ; Limpens, Juul ; Linkosalmi, Maiju ; Ma, Jin Ze ; Mauritz, Marguerite ; Munir, Tariq M. ; Natali, Susan M. ; Natcheva, Rayna ; Noskova, Maria ; Payne, Richard J. ; Pilkington, Kyle ; Robinson, Sean ; Robroek, Bjorn J.M. ; Rochefort, Line ; Singer, David ; Stenøien, Hans K. ; Tuittila, Eeva Stiina ; Vellak, Kai ; Verheyden, Anouk ; Michael Waddington, James ; Rice, Steven K. - \ 2018
    Biogeosciences 15 (2018)16. - ISSN 1726-4170 - p. 5189 - 5202.

    Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and CO2 uptake from the atmosphere. As the isotopic composition of carbon (12,13C) and oxygen (16,18O) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of Sphagnum is species-specific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii) to what extent Sphagnum tissue δ18O tracks the δ18O isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia using two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in δ13C values between species. For S. magellanicum δ13C decreased with increasing height above the water table (HWT, R2 =17%) and was positively correlated to productivity (R2 = 7%). Together these two variables explained 46% of the between-site variation in δ13C values. For S. fuscum, productivity was the only significant predictor of δ13C but had low explanatory power (total R2 = 6%). For δ18O values, approximately 90% of the variation was found between sites. Globally modelled annual δ18O values in precipitation explained 69% of the between-site variation in tissue δ18O. S. magellanicum showed lower δ18O enrichment than S. fuscum (-0.83 ‰ lower). Elevation and climatic variables were weak predictors of tissue δ18O values after controlling for δ18O values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue δ18O values from modelled annual δ18O values in precipitation, and (b) the possibility of relating tissue δ13C values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.

    Can frequent precipitation moderate drought impact on peatmoss carbon uptake in northern peatlands?
    Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2015
    climate change - Sphagnum fuscum - Sphagnum balticum - Sphagnum majus - desiccation tolerance - mires - moisture stress - photosynthesis - rain variability - Sphagnum physiology - water balance
    Northern peatlands represent a large global carbon store that potentially can be destabilised by summer water table drawdown. Precipitation can moderate negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystems’ key species. Yet, the frequency for such rewetting to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, S. balticum and S. fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn, hummock) and expected to differ in their water table-precipitation relationships. Precipitation contributed significantly to peatmoss water supply at deep water tables, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency at deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation on carbon uptake by peatmosses. Yet, the potential to moderate drought impact is species-specific and dependents on the temporal distribution of precipitation.
    Can frequent precipitation moderate drought impact on peatmoss carbon uptake in northern peatlands?
    Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2014
    Plant functional types define magnitude of drought response in peatland CO2 exchange
    Kuiper, J.J. ; Mooij, W.M. ; Bragazza, L. ; Robroek, B.J.M. - \ 2014
    Ecology 95 (2014)1. - ISSN 0012-9658 - p. 123 - 131.
    sphagnum mosses - nitrogen availability - removal experiment - species-diversity - moisture controls - water-content - carbon - ecosystems - grassland - bog
    Peatlands are important sinks for atmospheric carbon (C), yet the role of plant functional types (PFTs) for C sequestration under climatic perturbations is still unclear. A plant-removal experiment was used to study the importance of vascular PFTs for the net ecosystem CO2 exchange (NEE) during (i.e., resistance) and after (i.e., recovery) an experimental drought. The removal of PFTs caused a decrease of NEE, but the rate differed between microhabitats (i.e., hummocks and lawns) and the type of PFTs. Ericoid removal had a large effect on NEE in hummocks, while the graminoids played a major role in the lawns. The removal of PFTs did not affect the resistance or the recovery after the experimental drought. We argue that the response of Sphagnum mosses (the only PFT present in all treatments) to drought is dominant over that of coexisting PFTs. However, we observed that the moment in time when the system switched from C sink to C source during the drought was controlled by the vascular PFTs. In the light of climate change, the shifts in species composition or even the loss of certain PFTs are expected to strongly affect the future C dynamics in response to environmental stress.
    Can frequent precipitation moderate the impact of drought on peatmoss carbon uptake in northern peatlands?
    Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2014
    New Phytologist 203 (2014)1. - ISSN 0028-646X - p. 70 - 80.
    sphagnum mosses - climate-change - water-content - co2 exchange - soil respiration - vegetation - accumulation - desiccation - boreal - bog
    Northern peatlands represent a large global carbon store that can potentially be destabilized by summer water table drawdown. Precipitation can moderate the negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystem's key species. Yet, the frequency of such rewetting required for it to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, Sphagnum balticum and Sphagnum fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn and hummock) and expected to differ in their water table–precipitation relationships. Precipitation contributed significantly to peatmoss water supply when the water table was deep, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency for deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation in carbon uptake by peatmosses. Yet, the potential to moderate the impact of drought is species-specific and dependent on the temporal distribution of precipitation.
    Snow cover manipulation effects on microbial community structure and soil chemistry in a mountain bog
    Robroek, B.J.M. ; Heijboer, A. ; Jassey, V.E.J. ; Hefting, M.M. ; Rouwenhorst, T.G. ; Buttler, A. ; Bragazza, L. - \ 2013
    Plant and Soil 369 (2013). - ISSN 0032-079X - p. 151 - 164.
    freeze-thaw cycles - rv-coefficient - climate-change - tundra soils - forest soil - nitrogen - dynamics - biomass - variability - trends
    Background and Aims Alterations in snow cover driven by climate change may impact ecosystem functioning, including biogeochemistry and soil (microbial) processes. We elucidated the effects of snow cover manipulation (SCM) on above-and belowground processes in a temperate peatland. Methods In a Swiss mountain-peatland we manipulated snow cover (addition, removal and control), and assessed the effects on Andromeda polifolia root enzyme activity, soil microbial community structure, and leaf tissue and soil biogeochemistry. Results Reduced snow cover produced warmer soils in our experiment while increased snow cover kept soil temperatures close-to-freezing. SCM had a major influence on the microbial community, and prolonged ‘close-to-freezing’ temperatures caused a shift in microbial communities toward fungal dominance. Soil temperature largely explained soil microbial structure, while other descriptors such as root enzyme activity and pore-water chemistry interacted less with the soil microbial communities. Conclusions We envisage that SCM-driven changes in the microbial community composition could lead to substantial changes in trophic fluxes and associated ecosystem processes. Hence, we need to improve our understanding on the impact of frost and freeze-thaw cycles on the microbial food web and its implications for peatland ecosystem processes in a changing climate; in particular for the fate of the sequestered carbon.
    Restoration of a Terrestrialized Soak Lake of an Irish Raised Bog: Results of Field Experiments
    Crushell, P.H. ; Smolders, A.J.P. ; Schouten, M.G.C. ; Robroek, B.J.M. ; Wirdum, G. van; Roelofs, J.G.M. - \ 2011
    Restoration Ecology 19 (2011)2. - ISSN 1061-2971 - p. 261 - 272.
    floating raft formation - cut-over bogs - methane production - peat quality - sphagnum - temperature - vegetation - groundwater - consumption - substrate
    Soaks (areas of mesotrophic/minerotrophic vegetation within acid bog) add to the overall heterogeneity and biodiversity of raised bog landscapes due to the presence of flora and fauna communities not typically associated with acid bog systems. A field experiment was set up to investigate the potential to restore the minerotrophic and aquatic communities that previously occurred within a soak of an oceanic raised bog in Ireland, which has recently undergone acidification with the expansion of acid bog type vegetation. Three different treatments, control (intact sphagnaceous raft), permeable (sphagnaceous raft removed), and enclosed (sphagnaceous raft removed and plots isolated from surrounding surface water influence) were applied to a total of six plots (each measuring 4 × 4 m), each treatment consisting of two replicates. Within 3 years a sphagnaceous raft with similar vegetation to the surroundings had developed in both permeable plots, while aquatic communities similar to those that occurred at the site in the past had established within the enclosed pots. Our results show that with manipulation of local hydrology it is possible to recreate conditions suitable for aquatic plant communities that once characterized the site. The results also give an insight into the likely processes responsible for the initial terrestrialization of the entire soak over the past century. Application of the results in relation to the site and the widespread practice of restoring bog vegetation on degraded peatlands are discussed
    Increased N affects P uptake of eight grassland species: the role of root surface phosphatase activity.
    Fujita, Y. ; Robroek, B.J.M. ; Ruiter, P.C. de; Heil, G.W. ; Wassen, M.J. - \ 2010
    Oikos 119 (2010)10. - ISSN 0030-1299 - p. 1665 - 1673.
    arbuscular-mycorrhizal fungi - nitrogen deposition - phosphorus-nutrition - phaseolus-vulgaris - 2nd-year growth - acquisition - vegetation - plants - availability - fertilization
    Increased N deposition may change species composition in grassland communities by shifting them to P limitation. Interspecific differences in P uptake traits might be a crucial yet poorly understood factor in determining the N effects. To test the effects of increased N supply (relative to P), we conducted two greenhouse fertilization experiments with eight species from two functional groups (grasses, herbs), including those common in P and N limited grasslands. We investigated plant growth and P uptake from two P sources, orthophosphate and not-readily available P (bound-P), under different N supply levels. Furthermore, to test if the N effects on P uptake was due to N availability alone or altered N:P ratio, we examined several uptake traits (root-surface phosphatase activity, specific root length (SRL), root mass ratio (RMR)) under varying N:P supply ratios. Only a few species (M. caerulea, A. capillaris, S. pratensis) could take up a similar amount of P from bound-P to that from orthophosphate. These species had neither higher SRL, RMR, phosphatase activity per unit root (Paseroot), nor higher total phosphatase activity (Pasetot: Paseroot times root mass), but higher relative phosphatase activity (Paserel: Pasetot divided by biomass) than other species. The species common from P-limited grasslands had high Paserel. P uptake from bound-P was positively correlated with Pasetot for grasses. High N supply stimulated phosphatase activity but decreased RMR and SRL, resulting in no increase in P uptake from bound-P. Paseroot was influenced by N:P supply ratio, rather than by only N or P level, whereas SRL and RMR was not dominantly influenced by N:P ratio. We conclude that increased N stimulates phosphatase activity via N:P stoichiometry effects, which potentially increases plant P uptake in a species-specific way. N deposition, therefore, may alter plant community structure not only by enhancing productivity, but also by favouring species with traits that enable them to persist better under P limited conditions
    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.
    How nitrogen and sulphur addition, and a single drought event affect root phosphatase activity in Phalaris arundinacea
    Robroek, B.J.M. ; Adema, E.B. ; Venterink, H.O. ; Leonardson, L. ; Wassen, M.J. - \ 2009
    Science of the Total Environment 407 (2009)7. - ISSN 0048-9697 - p. 2342 - 2348.
    fresh-water wetlands - species richness - phosphorus limitation - eutrophication - deposition - biomass - fertilization - grasslands - growth - carbon
    Conservation and restoration of fens and fen meadows often aim to reduce soil nutrients, mainly nitrogen (N) andphosphorus (P). The biogeochemistry of P has received much attention as P-enrichment is expected to negatively impact on species diversity in wetlands. It is known that N, sulphur (S) and hydrological conditions affect the biogeochemistry of P, yet their interactive effects on P-dynamics are largely unknown. Additionally, in Europe, climate change has been predicted to lead to increases in summer drought. We performed a greenhouse experiment to elucidate the interactive effects of N, S and a single drought event on the P-availability for Phalaris arundinacea. Additionally, the response of plant phosphatase activity to these factors was measured over the two year experimental period. In contrast to results from earlier experiments, our treatments hardly affected soil P-availability. This may be explained by the higher pH in our soils, hampering the formation of Fe-P or Fe-Al complexes. Addition of S, however, decreased the plants N:P ratio, indicating an effect of S on the N:P stoichiometry and an effect on the plant's P-demand. Phosphatase activity increased significantly after addition of S, but was not affected by the addition of N or a single drought event. Root phosphatase activity was also positively related to plant tissue N and P concentrations, plant N and P uptake, and plant aboveground biomass, suggesting that the phosphatase enzyme influences P-biogeochemistry. Our results demonstrated that it is difficult to predict the effects of wetland restoration, since the involved mechanisms are not fully understood. Short-term and long-term effects on root phosphatase activity may differ considerably. Additionally, the addition of S can lead to unexpected effects on the biogeochemistry of P. Our results showed that natural resource managers should be careful when restoring degraded fens or preventing desiccation of fen ecosystems.
    The disappearance of S. imbricatum from European raised bogs: a comment on McClymont et al.
    Robroek, B.J.M. ; Waucomont, J. ; Schouten, M.G.C. - \ 2009
    Holocene 19 (2009)7. - ISSN 0959-6836 - p. 1093 - 1094.
    McClymont et al. (The Holocene 18 (2008) 991—1002) present data on several environmental proxies to explore the disappearance of Sphagnum imbricatum from a peat bog in northern England, Wales and Ireland, respectively. McClymont et al. used their results to argue that a combination of rapid water-table rise and increased aeolian nutrient input from surrounding (agricultural) areas may have caused the disappearance of S. imbricatum from European raised bogs. The paper contributes to a growing body of literature focusing on the ‘abrupt’ decline of S. imbricatum (S. austinii) AD 1000—1700. From the literature it becomes apparent that determining the exact mechanism for the decline of S. imbricatum (S. austinii) is difficult. Hence, many potential mechanisms have been suggested, amongst which increased wetness, increased interspecific competition, local burning and increased nutrient input are just a few examples. Although we do not comment on the quality of the science, there are a few things to be considered in order to get a complete picture.
    Sphagnum re-introduction in degraded peatlands: the effects of aggregation, species and water table
    Robroek, B.J.M. ; Ruijven, J. van; Schouten, M.G.C. ; Breeuwer, A.J.G. ; Crushell, P.H. ; Berendse, F. ; Limpens, J. - \ 2009
    Basic and Applied Ecology 10 (2009)8. - ISSN 1439-1791 - p. 697 - 706.
    experimental plant-communities - interspecific competition - vascular plants - growth - bog - mosses - heterogeneity - restoration - vegetation - dynamics
    In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (¿5 and ¿20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.
    Response of Sphagnum species mixtures to increased temperature and nitrogen availability
    Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Berendse, F. ; Gleichman, J.M. ; Robroek, B.J.M. ; Limpens, J. - \ 2009
    Plant Ecology 204 (2009)1. - ISSN 1385-0237 - p. 97 - 111.
    n-deposition - water-level - nutritional constraints - decomposition rates - northern peatlands - litter quality - climate-change - peat formation - growth - bogs
    To predict the role of ombrotrophic bogs as carbon sinks in the future, it is crucial to understand how Sphagnum vegetation in bogs will respond to global change. We performed a greenhouse experiment to study the effects of two temperature treatments (17.5 and 21.7°C) and two N addition treatments (0 and 4 g N m¿2 year¿1) on the growth of four Sphagnum species from three geographically interspersed regions: S. fuscum, S. balticum (northern and central Sweden), S. magellanicum and S. cuspidatum (southern Sweden). We studied the growth and cover change in four combinations of these Sphagnum species during two growing seasons. Sphagnum height increment and production were affected negatively by high temperature and high N addition. However, the northern species were more affected by temperature, while the southern species were more affected by N addition. High temperature depressed the cover of the `wet¿ species, S. balticum and S. cuspidatum. Nitrogen concentrations increased with high N addition. N:P and N:K ratios indicated P-limited growth in all treatments and co-limitation of P and K in the high N treatments. In the second year of the experiment, several containers suffered from a severe fungal infection, particularly affecting the `wet¿ species and the high N treatment. Our findings suggest that global change can have negative consequences for the production of Sphagnum species in bogs, with important implications for the carbon sequestration in these ecosystems
    Hoogveenherstel in Nederland: meer dan een droom
    Robroek, B.J.M. ; Eppinga, M.B. ; Limpens, J. ; Wassen, M.J. ; Schouten, M.G.C. - \ 2009
    Landschap : tijdschrift voor landschapsecologie en milieukunde 26 (2009)1. - ISSN 0169-6300 - p. 17 - 26.
    hoogveengebieden - vegetatie - herstel - natuurontwikkeling - moorlands - vegetation - rehabilitation - nature development
    Vernatten, de belangrijkste herstelmaatregel in hoogveenrestanten, heeft niet altijd het gewenste effect. Waarom dat zo is, is grotendeels nog onbekend. De auteurs beargumenteren dat recente inzichten uit empirische en experimentele studies in hoogveenherstelprojecten moeten worden gebruikt om de bestaande theoretische modellen uit te breiden, om deze vervolgens te kunnen gebruiken in het ontwikkelen van effectieve, gebiedspecifieke herstelplannen. Hierdoor kan de droom van zelfregulerende hoogvenen in Nederland wellicht op niet al te lange termijn werkelijkheid worden.
    Interactive effects of water table and precipitation on net CO2 assimilation of three co-occurring Sphagnum mosses differing in distribution above the water table
    Robroek, B.J.M. ; Schouten, M.G.C. ; Limpens, J. ; Berendse, F. ; Poorter, H. - \ 2009
    Global Change Biology 15 (2009)3. - ISSN 1354-1013 - p. 680 - 691.
    peat bog - photosynthesis - exchange - desiccation - level - growth - fuscum - temperature - tolerance - biomass
    Sphagnum cuspidatum, S. magellanicum and S. rubellum are three co-occurring peat mosses, which naturally have a different distribution along the microtopographical gradient of the surface of peatlands. We set out an experiment to assess the interactive effects of water table (low: -10 cm and high: -1 cm) and precipitation (present or absent) on the CO2 assimilation and evaporation of these species over a 23-day period. Additionally, we measured which sections of the moss layer were responsible for light absorption and bulk carbon uptake. Thereafter, we investigated how water content affected carbon uptake by the mosses. Our results show that at high water table, CO2 assimilation of all species gradually increased over time, irrespective of the precipitation. At low water table, net CO2 assimilation of all species declined over time, with the earliest onset and highest rate of decline for S. cuspidatum. Precipitation compensated for reduced water tables and positively affected the carbon uptake of all species. Almost all light absorption occurred in the first centimeter of the Sphagnum vegetation and so did net CO2 assimilation. CO2 assimilation rate showed species-specific relationships with capitulum water content, with narrow but contrasting optima for S. cuspidatum and S. rubellum. Assimilation by S. magellanicum was constant at a relatively low rate over a broad range of capitulum water contents. Our study indicates that prolonged drought may alter the competitive balance between species, favoring hummock species over hollow species. Moreover, this study shows that precipitation is at least equally important as water table drawdown and should be taken into account in predictions about the fate of peatlands with respect to climate change
    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.
    Vegetation feedbacks on surface water availability in bogs
    Limpens, J. ; Robroek, B.J.M. ; Heijmans, M.M.P.D. - \ 2008
    Patch sixe and species identity affect the hydrology along the surface on Sphagnum dominated peatlands
    Limpens, J. ; Robroek, B.J.M. ; Schouten, M.G.C. - \ 2008
    The effect of increased temperature and nitrogen deposition on decomposition in bogs
    Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Robroek, B.J.M. ; Limpens, J. ; Berendse, F. - \ 2008
    Oikos 117 (2008)8. - ISSN 0030-1299 - p. 1258 - 1268.
    plant-mediated controls - swedish raised bog - litter quality - sphagnum mosses - mass-loss - growth - carbon - rates - decay - fertilization
    Despite their low primary production, ombrotrophic peatlands have a considerable potential to store atmospheric carbon as a result of their extremely low litter decomposition rates. Projected changes in temperature and nitrogen (N) deposition may increase decomposition rates by their positive effects on microbial activity and litter quality, which can be expected to result in enhanced mass loss and N release from Sphagnum and vascular plant litter. This is the first study that examines the combined effects of increased temperature and N deposition on decomposition in bogs. We investigated mass loss and N release at four bog sites along a gradient from north Sweden to northeast Germany in which both temperature and N deposition increased from north to south. We performed two litterbag experiments: one reciprocal experiment with Eriophorum vaginatum litter and one experiment using recalcitrant (Sphagnum fuscum) and more degradable (Sphagnum balticum) Sphagnum litter collected from the most northern site. We measured mass loss and N release during two (Sphagnum) and three (E. vaginatum) years. The N concentration and decomposability of the E. vaginatum litter did not differ between the sites. Mass loss from E. vaginatum litter increased over the gradient from north to south, but there was no such effect on Sphagnum litter. N loss of all litter types was affected by collection site, incubation site and time and all interactions between these factors. N release in Sphagnum was positively related to N concentration. We conclude that decomposition of vascular plants and Sphagnum litter is influenced by different environmental drivers, with enhanced temperatures stimulating mass loss of vascular plant litter, but not of Sphagnum. Enhanced N deposition increases Sphagnum litter N loss. As long-term consequences of climate change will presumably entail a higher vascular plant production, overall litter decomposition rates are likely to increase, especially in combination with increased temperature
    Mixing ratio and species affect the use of substrate-derived CO2 by Sphagnum
    Limpens, J. ; Robroek, B.J.M. ; Heijmans, M.M.P.D. ; Tomassen, H.B.M. - \ 2008
    Journal of Vegetation Science 19 (2008)6. - ISSN 1100-9233 - p. 841 - 848.
    carbon-dioxide - water-content - photosynthesis - growth - permeability - desiccation - vegetation - mosses
    Question: Can mixing ratio and species affect the use of substrate-derived CO2 by Sphagnum? Location: Poor fen in south Sweden and greenhouse in Wageningen, The Netherlands. Methods: Two mixing ratios of Sphagnum cuspidatum and S. magellanicum were exposed to two levels of CO2 by pumping CO2 enriched and non-enriched water through aquaria containing the species mixtures in the greenhouse. Results: Enhanced CO2 stimulated the production of S. cuspidatum, but only in aquaria co-dominated by S. magellanicum, coinciding with higher CO2 concentrations in the water layer. The denser growing S. magellanicum seemed to reduce gas escape from the water, resulting in accumulation of dissolved CO2. Adding CO2 did not affect species replacement. Conclusions: The use of substrate-derived CO2 for Sphagnum production depended on species identity and mixing ratio. The effect of mixing ratio on CO2 concentrations in the water layer suggests that species composition may affect both the efficiency with which substrate-derived CO2 is trapped and subsequently used. This could result in hitherto unexplored feedbacks between vegetation composition and gas exchange.
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