Expansion of invasive species on ombrotrophic bogs: desiccation or high N deposition?

Abstract

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. Synthesis and applications. We conclude that the invasion of bogs by Molinia andBetula 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.

Effects of nitrogen fertilization on diazotrophic activity of microorganisms associated with Sphagnum magellanicum

“…The effects of high N deposition are most severe in nutrient-poor ecosystems such as Sphagnum-dominated peatlands, which are very sensitive to increased nutrient influx (Lamers et al 2000;Tomassen et al 2004;Verhoeven et al 2011;Novak et al 2015). Here, additional N supply might lead to higher biomass production and therefore carbon sequestration, but an opposite or mixed effect can also be envisaged: N in the form of nitrate/nitrite could serve as electron acceptor for peat degradation, and increase degradability of otherwise very recalcitrant peat bog biomass (via an BimprovedĈ :N stoichiometry and/or induced shifts from Sphagnum to vascular plants (Bragazza et al 2012)), with greenhouse gases carbon dioxide (CO 2 ) and methane (CH 4 ) being the products of this oxygen-limited degradation.…”

A Native Species with Invasive Behaviour in Coastal Dunes: Evidence for Progressing Decay and Homogenization of Habitat Types

“…This development parallels the development in the grass Molinia caerulea some 30 years ago in Holland, where the grass invaded dry inland heaths. Homogenisation of terrestrial ecosystems as acid grasslands (Stevens et al 2004), heathlands (Bobbink et al 1998), ombrotrophic bogs (Tomassen et al 2004), and dunes manifests itself through increased cover of tall graminoids and a decrease in small herbs and lichens (Remke et al 2009). The changes of the vegetation in heathlands and bogs in the Netherlands in the late 1970s/ early 1980s (Heil and Diemont 1983;Aerts and Berendse 1988) did not manifest itself in Denmark till one or two decades later.…”

From land to water, an overview of organic matter research in France––proceedings of the Sainte-Maxime 2009 symposium organized by the French network on organic matter research

“…In peatlands, it stimulates the growth of vascular invading species, which causes the decline of Sphagnum species (Tomassen et al 2004) and affects OM dynamics. The litter of invading species indeed exhibits higher degradability and higher nutrient contents in comparison with Sphagnum, which promote the decay of OM .…”