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

Abstract

asterisk inside a circle sign In Dutch fens, subjected to high nitrogen (N) deposition, Scorpidium and other brown mosses have declined markedly. A concurrent strong increase of Sphagnum and Polytrichum has promoted acidification. We measured nitrate (NO3-) and ammonium (IMH4+) availability in Dutch fens. We also tested preference for either N form of Scorpidium scorpioides, Sphagnum squarrosum and Polytrichum commune. asterisk inside a circle sign Ion exchange membranes were installed in the field. In a hydroponic experiment, plants were grown on 100 μM (reflecting concentrations in Dutch precipitation since 1980), provided as NO3-, NH4NO3, or NH 4+. asterisk inside a circle sign NH4+ availability in Sphagnum and Polytrichum stands and NH 4+:NO3- ratio in Sphagnum stands were higher than in brown moss stands. In the experiment, Scorpidium performed best on NO3-. NH4NO3 tended to decrease its growth, whereas NH4+ was very toxic. N treatment did not significantly affect growth of Sphagnum and Polytrichum. Tissue pH and nutrient concentrations confirmed the growth patterns and indicated that Scorpidium was most sensitive to NH4+ stress. asterisk inside a circle sign We conclude that high NH4+ inputs pose a serious threat to the brown moss flora of rich fens. © New Phytologist (2004).