Long-term interactive effects of N addition with P and K availability on N status of Sphagnum

Abstract

Little information exists concerning the long-term interactive effect of nitrogen (N) addition with phosphorus (P) and potassium (K) on Sphagnum N status. This study was conducted as part of a long-term N manipulation on Whim bog in south Scotland to evaluate the long-term alleviation effects of phosphorus (P) and potassium (K) on N saturation of Sphagnum (S. capillifolium). On this ombrotrophic peatland, where ambient deposition was 8 kg N ha yr, 56 kg N ha yr of either ammonium (NH, N) or nitrate (NO, N) with and without P and K, were added over 11 years. Nutrient concentrations of Sphagnum stem and capitulum, and pore water quality of the Sphagnum layer were assessed. The N-saturated Sphagnum caused by long-term (11 years) and high doses (56 kg N ha yr) of reduced N was not completely ameliorated by P and K addition; N concentrations in Sphagnum capitula for N 56 PK were comparable with those for N 56, although N concentrations in Sphagnum stems for N 56 PK were lower than those for N 56. While dissolved inorganic nitrogen (DIN) concentrations in pore water for N 56 PK were not different from N 56, they were lower for N 56 PK than for N 56 whose stage of N saturation had not advanced compared to N 56. These results indicate that increasing P and K availability has only a limited amelioration effect on the N assimilation of Sphagnum at an advanced stage of N saturation. This study concluded that over the long-term P and K additions will not offset the N saturation of Sphagnum.

Does Shift in Vegetation Abundance After Nitrogen and Phosphorus Additions Play a Key Role in Regulating Fungal Community Structure in a Northern Peatland?

“…Unexpectedly, long-term addition of P also reduced Sphagnum cover as well as the relative abundance of Sphagnum -associated fungi instead of alleviating the negative effect of N addition, which is inconsistent with our fourth hypothesis. This result supports the notion that there is only a limited alleviating effect of P addition on excess N ( Fritz et al, 2012 ; Chiwa et al, 2018 ), likely owing to imposed physiological stress ( Fritz et al, 2012 ). Collectively, with regard to our fourth hypothesis, we did observe that long-term N addition decreased the relative abundance of Sphagnum -associated fungi, but P addition did not alleviate the negative effect of excess N input.…”

Sphagnumgrowth under N saturation: interactive effects of water level and P or K fertilization

“…Chiwa et al . ); unfortunately, this was not measured in our study. Li et al (), however, we did not find changes in P concentration either in the capitula (0–1 cm) or in the stem (1–4 cm) of S. papillosum at different P fertilization levels.…”

“…In other studies, with low P concentrations in the pore water, similarly high P concentrations in the mosses were found only after P fertilization (Chiwa et al . , Limpens et al ; Limpens et al ; Limpens & Heijmans ; Fritz et al ). As in our study, Sphagnum did not respond significantly to additional P (Li et al ; Limpens et al ) at sites with similar water P concentrations as in our experiment (0.23 mg·l −1 ) and in natural bogs in Lower Saxony (Bertram ; Lütt ).…”

P and K additions enhance canopy N retention and accelerate the associated leaching

“…the phosphatase enzymes, to enhance P availability , thus delaying the onset of P limitation (Marklein and Houlton 2012;Maistry et al 2015). If a higher leaf N:P ratio is indicative of N saturation diagnosed from the leaf stoichiometry in wetlands (Koerselman and Meuleman 1996;Güewell 2004;Chiwa et al, 2018), then the small increases in foliar N:P ratio of Calluna exposed to different levels of N addition without P and K even after 11-years exposure ( Figure 8a) and decreases in the N:P ratio with P and K (Figure 8b), suggest that N exposure at this site does not cause N saturation in Calluna even for the high N dose without P and K addition. Chiwa et al (2018) showed that Sphagnum tissue N concentration at this same site also increased, whereas tissue P concentrations did not, in response to N dose.…”