Growth reduction of Sphagnum magellanicum subjected to high nitrogen deposition: the role of amino acid nitrogen concentration

Abstract

We tested the relationship between Sphagnum growth and the amount of nitrogen stored in free amino acids in a fertilisation experiment with intact peat monoliths in an open greenhouse in The Netherlands. Three nitrogen deposition scenarios were used: no nitrogen deposition, field conditions and a doubling of the latter, corresponding to 0, 40 and 80 kg N ha(-1 )year(-1). Growth of Sphagnum as expressed by height increment was reduced in the 80 kg N treatment, but showed no correlation with the total nitrogen tissue concentration or with the concentration of individual or pooled free amino acids. The amount of nitrogen stored in free amino acids increased concomitantly with deposition, although it lagged more and more behind the total nitrogen concentration, the latter pointing to the accumulation of unmeasured nitrogen compounds. Asparagine clearly acted as the major storage compound for nitrogen in Sphagnum stem tissue, whereas arginine fulfilled this function to a lesser extent in the capitulum. It appears that nitrogen-induced growth inhibition of Sphagnum is related to acclimation rather than to certain threshold concentrations of amino nitrogen or total nitrogen. We propose that when Sphagnum is exposed to a step increase of nitrogen, its nitrogen metabolism does not adapt fast enough to keep up with the enhanced uptake rate. This imbalance between nitrogen uptake and assimilation may lead to an accumulation of toxic NH(4)(+ )in the cell and a subsequent reduction in growth.

Response of Sphagnum species mixtures to increased temperature and nitrogen availability

“…The negative effect of the high N treatment on height increment in all combinations is probably mainly the result of direct toxic effects of the high N concentration on Sphagnum, as found in other studies with N deposition above 4 g N m -2 year -1 (Gunnarsson and Rydin 2000; Limpens and Berendse 2003a;Nordin and Gunnarsson 2000). As the N:P ratios were already relatively high at the start of our experiment, with values of 25 or higher, this might indicate that Sphagnum was already P limited, since P limitation occurs at high N:P ratios ([15 according to Aerts et al 1992; [30 according to Bragazza et al 2004).…”

“…Although the effects of temperature (Asada et al 2003;Dorrepaal et al 2003;Gerdol 1995) and N (Aerts et al 2001;Gerdol et al 2007;Limpens and Berendse 2003a) on growth of different Sphagnum species have been studied, and a few studies have examined their separate effects on mixtures of Sphagnum species (Breeuwer et al 2008a;Gunnarsson and Rydin 2000;Robroek et al 2007a), only one study (Wiedermann et al 2007) has examined the combined effects of temperature and N on Sphagnum cover. Since global warming can indirectly cause increased nutrient availability through increased decomposition and N mineralisation in bogs (Hobbie 1996;Rustad et al 2001), it is even more important to study the effects of increased temperature and N availability together in order to predict the effect of global change on Sphagnum vegetation.…”

Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

“…There were no significant effects on P max , L SP , L CP and U in the high-elevation population under N addition. It has been thought that plants vary their reactions to N addition (Limpens and Berendse 2003;Clark and Tilman 2008;Bobbink et al 2010). Our results provided further evidence that the negative effects on photosynthesis are greater in low-elevation population than in high-elevation population.…”

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

“…incorporation in N-rich amino acids: cf. Näsholm et al, 1994;Limpens & Berendse, 2003). Such a detoxification mechanism may be much less developed in brown mosses, which are, in undisturbed habitats, subjected to low external NH 4 + concentrations and comparatively high concentrations of nontoxic NO 3 -.…”