Short-Term Physiological Responses of Mosses to Atmospheric Ammonium and Nitrate

ISSN： 0049-6979

Source： Water, Air, and Soil Pollution, Vol.93, Iss.1-4, 1997-01, pp. : 225-242

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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 and Philonotis fontana, in response to a single field misting with 3 mol $$m^{-3}NH_4^+$$and $$NO_3^-$$. Increases of 20% were recorded for tissue N content, 48 hr after misting with N containing solutions. When labelled $$^{15}NH_4^+$$ or $$^{15}NO_3^-$$ were applied to R. Lanuginosum at 1, 3 and 6 mol$$m^{-3}$$ concentrations, partitioning of incorporated $$^{15}N$$ 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.