Ecophysiological adjustment of two Sphagnum species in response to anthropogenic nitrogen deposition

Here, it was investigated whether Sphagnum species have adjusted their nitrogen (N) uptake in response to the anthropogenic N deposition that has drastically altered N-limited ecosystems, including peatlands, worldwide.A lawn species, Sphagnum balticum, and a hummock species, Sphagnum fuscum, were collected from three peatlands along a gradient of N deposition (2, 8 and 12 kg N ha(-1) yr(-1)) The mosses were subjected to solutions containing a mixture of four N forms. In each solution one of these N forms was labeled with (15)N (namely (15)NH(4)(+) (15)NO(3)(-) and the amino acids [(15)N] alanine (Ala) and [(15)N] glutamic acid (Glu)).It was found that for both species most of the N taken up was from, followed by Ala, Glu, and very small amounts from. At the highest N deposition site N uptake was reduced, but this did not prevent N accumulation as free amino acids in the Sphagnum tissues.The reduced N uptake may have been genetically selected for under the relatively short period with elevated N exposure from anthropogenic sources, or may have been the result of plasticity in the Sphagnum physiological response. The negligible Sphagnum NO(3)(-) uptake may make any NO(3)(-) deposited readily available to co- occurring vascular plants.