Nitrogen and phosphorus in mire plants: variation during 50 years in relation to supply rate and vegetation type

Abstract

2005. Nitrogen and phosphorus in mire plants: variation during 50 years in relation to supply rate and vegetation type. Á/ Oikos 109: 539 Á/554.Southern Sweden has long been exposed to an increasing atmospheric nitrogen deposition. We investigated the effects of this supply on the Sphagnum mire vegetation in SW Gö taland by comparing above-ground tissue concentrations of N and P and biomass variables in five vascular plant and two Sphagnum species collected during three periods since 1955 at 81 sites representing three vegetation types, viz. ombrotrophic bog, extremely poor fen and moderately poor fen, within two areas differing in annual N deposition. The N:P ratios in the plants were rarely below 17, suggesting P as the growth-limiting mineral nutrient. In the vascular plants both growth and concentrations of N and P were highest in the moderately poor fen sites because of a higher mineralization rate, the differences between the extremely poor fen and bog sites being smaller in these respects. In the extremely poor fen and bog sites the N concentrations were slightly higher in the area with the highest N deposition. From 1955 to 2002 the concentration of N in the Sphagnum spp. increased proportionally to the supply rate while P remained constant. In the vascular plants the concentrations of P remained constant while N showed slightly decreasing trends in the bog and extremely poor fen sites, but since the size of the plants increased the biomass content of N and P increased, too. The increased N deposition has had its greatest effects on the site types with the highest Sphagnum biomass and peat accumulation rate. The high N concentration in the Sphagnum mosses probably reduced their competitiveness and facilitated the observed expansion of vascular plants. However, the increased N deposition might also have triggered an increased mineralization in the acrotelm increasing the supply of P to the vascular plants and thus also their productivity. This may also explain the slightly higher productivity among the vascular plants in the area with the highest N deposition rate. In conclusion, it seems as the increased N deposition has directly influenced only the growth of the Sphagnum mosses and that the effects on the growth of the vascular plants are indirect.Sphagnum mires Á/ ombrotrophic bogs and rheotrophic (or minerotrophic) fens dominated by peat mosses Á/ are looked upon as poor in mineral nutrients. The main differentiation in the vegetation is seen as a result of rheotrophic fens being less acid and richer in minerals, particularly calcium, than ombrotrophic bogs, because of a supply by water from the surrounding drainage area in addition to the supply by the atmospheric deposition that is the only source for ombrotrophic sites. Most bog plants are also characterised by relatively low leaf concentrations of N and P and high nutrient use efficiencies (Aerts et al. 1999). The low availability of N and P in Sphagnum -mires results partly from low mineralization rates and partly from the losses associated with t...

Resource contrast in patterned peatlands increases along a climatic gradient

“…Second, if the different rooting patterns of the three plant species had affected the resource contrast, this would have most likely been a weakening effect rather than an explanatory factor. More specifically, in Siberia and Sweden we sampled Carex lasiocarpa and E. vaginatum, which are characterized by a long vertical root system (Granberg et al 2001, Malmer andWalle´n 2005), and therefore may be better able to attract nutrients from deeper layers (and thus smooth out possible hummock-hollow differences in nutrient availability) as compared to the more shallow-rooting Rhynchospora alba (Malmer and Walle´n 2005) that was sampled in the Scottish site.…”

Effects of N and P fertilization on the greenhouse gas exchange in two northern peatlands with contrasting N deposition rates

“…15 kg N ha −1 yr −1 . In a longer time perspective, this may act to decrease the net C sink in this ecosystem (Berendse et al, 2001;Malmer and Wallén, 2005).…”

“…Nutrient-poor peatlands (bogs) are generally dominated by Sphagnum mosses. They have the ability to intercept airborne nutrients, providing a competitive advantage over vascular plants that rely on nutrient uptake by roots (Malmer and Wallén, 2005). However, at high levels of N input the Sphagnum filter will become saturated, and additional N will leach down to the vascular plant root zone enhancing growth of vascular plants (Lamers et al, 2000;Rydin and Jeglum, 2006).…”

“…However, at high levels of N input the Sphagnum filter will become saturated, and additional N will leach down to the vascular plant root zone enhancing growth of vascular plants (Lamers et al, 2000;Rydin and Jeglum, 2006). An increased abundance of vascular plants may reduce C sequestration due to the shift towards more easily decomposable litter (Berendse et al, 2001;Malmer and Wallén, 2005). Previous studies have also shown that very high rates of N deposition may lead to accumulation of toxic NH 4 + in the Sphagnum cell resulting in growth reduction; Limpens and Berendse (2003) found that Sphagnum growth was reduced at deposition rates of 80 kg N ha −1 yr −1 , but not at 40 kg N ha −1 yr −1 .…”

Physiological responses to nitrogen and sulphur addition and raised temperature in Sphagnum balticum

“…According to the model, PNUE has its maximum at N concentration 9.1 mg g -1 . Data were retrieved from the present study (open triangles S plots excluded because they had a negative effect on photosynthetic rate) and from Granath et al (2009) caused by indirect effects such as increased shading from vascular plants (Berendse et al 2001;Limpens et al 2003a;Gunnarsson et al 2004), infections from parasitic fungi and epiphytic algae (Limpens et al 2003b), or nutrient imbalance (Bragazza et al 2004;Malmer and Wallén 2005). Although changed photosynthetic capacity may not be the mechanism behind impoverished performance of S. balticum under high N deposition, differences among Sphagnum species in optimum N levels and N tolerance (i.e.…”