Stimulated growth of Betula pubescens and Molinia caerulea on ombrotrophic bogs: role of high levels of atmospheric nitrogen deposition

Abstract

Summary 1In order to test whether the observed invasion of ombrotrophic bogs in the Netherlands by Molinia caerulea and Betula pubescens is the result of long-term high nitrogen (N) loads, we conducted a 3-year fertilization experiment with Sphagnum fallax turfs. Six different N treatments were applied ranging from 0 (control) to 4 g N m − 2 year − 1 . 2 During the experimental period, ammonium concentrations in the peat moisture remained very low due to high uptake rates by Sphagnum . Tissue N concentrations in S. fallax showed a linear response to the experimental N addition. Excess N was accumulated as N-rich free amino acids such as arginine, asparagine and glutamine, especially at N addition rates of 0.25 g m − 2 year − 1 or higher, indicating N-saturation. 3 Despite the high tissue N : P ratio (above 35), above-ground biomass production by Molinia was still stimulated at N addition rates of 4 g m − 2 year − 1 , and foliar nutrient concentrations were unaffected compared to the control. In contrast to Molinia , Betula was unable to increase its above-ground biomass. Foliar N concentrations in Betula were significantly higher at N addition rates of 4 g m − 2 year − 1 and excess N was stored in foliar arginine, making up 27% of the total N concentration. Evapotranspiration was increased at higher N addition rates due to stimulated total above-ground biomass production of the vegetation. 4 N addition at the actual Dutch deposition rate of 4 g m − 2 year − 1 stimulated the growth of Molinia in this experiment, providing evidence that the observed dominance of Molinia on ombrotrophic bogs in the Netherlands is caused by high N deposition levels. Based on the observed changes in biomass production and tissue nutrient concentrations, we assume that a long-term deposition of 0.5 g N m − 2 year − 1 , or higher, leads to undesirable changes in species composition and increased risk of desiccation.

Influence of Nitrogen Fertilization on Wheat, and Soil Carbon, Nitrogen and Phosphorus Stoichiometry Characteristics

“…N fertilization significantly increased N concentrations in wheat (Fig. 1 c, d), which was observed in other studies (Ruohomaki et al, 1996;Tomassen et al, 2003;Esmeijer-Liu et al, 2009). At harvest, the grain N and P contents were higher, indicated that N and P in other parts of wheat transferred to the grain.…”

Toxicity of reduced nitrogen in eelgrass (Zostera marina) is highly dependent on shoot density and pH

“…Water samples taken during both experiments were analyzed for NH x and nitrate (Tomassen et al 2003). NH x concentrations were determined spectrophotometrically using hypochlorite.…”

“…After extraction, amino acid concentrations were measured after pre-column derivatisation with 9-Xuorenylmethyl-chloroformate (FMOC-Cl), using high pressure liquid chromatography (HPLC) (Tomassen et al 2003). C:N ratios and total N concentrations were determined in freeze-dried leaf tissues by an CNS analyzer (type NA1500; Carlo Erba Instruments, Milan, Italy).…”

Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

“…2c). Tomassen et al (2003) also reported lower pH in 381 peat moisture due to the uptake of NH4 + by Sphagnum. In contrast, higher pH in soil 382 pore water was observed for NO3 -treatments (Sheppard et al, 2014), probably due to…”

“…Pore water that has passed through the Sphagnum filter may differ in terms of 103 water quality including pH (Manninen et al, 2011;Sheppard et al, 2014) (Krupa, 2003;Staelens et al, 2008;Stevens et al, 2011) and hydrogen 108 ion (H + ) leaching (Krupa, 2003;Liu et al, 2013;Manninen et al, 2011;Paulissen et al, 109 2004; Stevens et al, 2011;Tomassen et al, 2003). In contrast, NO3 -uptake is 110 accompanied by hydroxyl ion (OH -) loss generated by nitrate reduction (Manninen et al,111 2011; Stevens et al, 2011).…”