Short-term physiological responses of mosses to atmospheric ammonium and nitrate

Abstract

Many bryophytes rely to a large extent on atmospheric deposition for their nutrient uptake. However, increasing levels of atmospheric ammonium (NH 4 + ) and nitrate (NO 3 - ) attract concern as to the possible harmful effects on bryophytes from these two nutrient sources. Changes in nitrate reductase (NR) activities, cation (Ca, K and Mg), total nitrogen (N) and organic acid concentrations were investigated for the mosses,Racomitrium lanuginosum, Rytidiadelphus loreus andPhilonotis fontana, in response to a single field misting with 3 mol−3 NH 4 + and NO 3 - . Increases of 20% were recorded for tissue N content, 48 hr after misting with N containing solutions. When labelled15NH 4 + or15NO 3 - were applied toR. Lanuginosum at 1, 3 and 6 mol m−3 concentrations, partitioning of incorporated15N between different tissue regions occured, with the highest N uptake in the upper stem and leaves. High concentrations of applied N resulted in reduced efficiency of N uptake. NH 4 + applications caused declines in NR activities, organic acids and cations, whereas, NO 3 - treatments caused the reverse response. Changes in cation contents, organic acids and NR activity reflect short-term regulation of N metabolism in the presence of defined N sources, as well as potential mechanisms of regulating cell pH homoeostasis. The consistency of physiological responses, especially NR activities, over short-term pollution episodes, provides evidence for their use as indicators of both NH 4 + and NO 3 - pollution.