Physiological and growth responses of the montane bryophyte Racomitrium lanuginosum to atmospheric nitrogen deposition

Abstract

Summary• The effects of nitrogen (N) deposition on the moss Racomitrium lanuginosum within montane heath in Scotland were investigated over 5 yr.• Permanent field plots were sprayed with KNO 3 or NH 4 Cl solutions, at doses equivalent to 10 and 40 kg N ha − 1 yr − 1 , in 3 -6 applications each summer.• Racomitrium growth and cover were severely reduced by N addition, whilst the proportion of dead shoots greatly increased. N dose decreased inducibility of shoot nitrate reductase activity (NRA), suggesting that N saturation of Racomitrium occurred, and caused an increase in potassium leakage. At high dosage, effects of NH 4 + were more detrimental than NO 3 -.• Physiological responses to N indicate that the habitat's critical load (CL) is exceeded by addition of 10 kg N ha − 1 yr − 1 . The differential toxicity of the two forms of N suggests that predominant ion type in deposition should be taken into consideration when CLs are set. In contrast to tissue N, NRA correlated well with shoot growth, and may thus be a useful biological indicator of moss condition.

Differential effects of nitrate and ammonium on three fen bryophyte species in relation to pollutant nitrogen input

“…In studies comparing the effects of NO 3 -and NH 4 + (at the same N concentration) on vascular plants, NH 4 + stress typically led to reduction in growth and survival rate, increased tissue N (often also P) concentration, and decreased tissue cation concentrations (Gigon & Rorison, 1972;De Graaf et al, 1998;Lucassen et al, 2003). Comparatively few studies have studied the separate effects of NO 3 -and NH 4 + on bryophytes and these have revealed the same patterns as described above for vascular plants (Soares & Pearson, 1997;Pearce et al, 2003). It has also been shown that NH 4 + toxicity can cause a decline in bryophyte cover (Krupa, 2003;Pearce et al, 2003).…”

“…It is well established that, because of their anatomy, bryophytes take up deposited elements very efficiently. However, this trait also makes them vulnerable, to a higher degree than vascular plants, to increased N deposition (Mäkipää, 1998;Proctor, 2000;Pearce et al ., 2003). Importantly, there are indications that at high deposition rates, NH 4 + may be more detrimental than NO 3 -, as Pearce et al .…”

Photosynthetic responses of two pleurocarpous mosses to low-level nitrogen addition: a study in an old-growth fir forest

“…Membrane damage to 'black' (lower) tissue has been reported in another montane moss Racomitrium lanuginosum (Hedw.) Brid (Pearce et al, 2003). Cell membranes play important roles in nutrient uptake and conservation (Glime, 2007).…”

Do Nitrogen Concentration and Forage Quality of the MossRacomitrium lanuginosumIncrease with Latitude?

“…Moss samples were oven dried, and the top 2 cm of shoots selected for analysis [11] to reflect recent growth. Samples were ground by ball mill and analysed for N and C concentration on a Fisons NA1500 NCS elemental analyser.…”

“…Thus whilst vascular plant N concentration is linked to soil N availability, moss N concentration is associated with atmospheric N deposition [10,11]. N deposition levels are lower in the Arctic than in heavily industrialised areas including northern Europe [12]; thus, a decrease in N concentration of moss in relation to latitude may be expected.…”