THE EFFECTS OF NITRATE, AMMONIUM AND TEMPERATURE ON NITRATE REDUCTASE ACTIVITY IN SPHAGNUM SPECIES

Abstract

SUMMARYThe effects of the availability of inorganic nitrogen on in vivo activity of nitrate reductase in Sphagnum capillifolium (Ehrh.) Hedw. and Sphagnum fuscum (Schimp.) Klinggr. were investigated in both field and laboratory experiments. Nitrate reductase activity per unit mass was highest in the capitulum and declined down the stem. Nitrate reductase activity was substrateinducible, maximum and total activities induced being correlated with the natural logarithm of nitrate concentration in the range 0 to 10 mM. Repeated treatment with 05 mM nitrate did not give rise to repeated similar patterns of nitrate reductase activity, induction decreasing with later successive applications. An initial ammonium treatment in a field experiment did not affect nitrate-induced enzyme activity. However, repeated applications of ammonium caused marked changes in the patterns of induction and a general repression of total nitrate reduction. This repression may result from both an effect of ammonium on nitrate uptake and a direct effect of the accumulation of ammonium or ammonium assimilation products on the enzyme itself. Repression by repeated nitrate supply may also operate in a similar way. The effects of ammonium and nitrate supply on the induction of nitrate reductase were shown to interact.The initial rate of induction of nitrate reductase activity increased with temperature, but prolonged nitrate supply resulted in highest enzyme levels at lowest temperatures. This effect may be due to greater rates of activity giving rise to greater repression by the products of nitrate assimilation at the higher temperatures. The results are discussed in relation to the use of nitrate reductase activity as a monitor of atmospheric nitrate deposition in ombrotrophic bryophyte species.

Effects of pollutants in snowmelt onKiaeria starkei, a characteristic species of late snowbed bryophyte dominated vegetation

“…Nitrate reductase activity was measured in vivo using the method described b} ' Woodin & Lee (1987). Activity was measured 8 h after treatment of the plants with 447 //eq 1"^ NaNOg to induce activity.…”

“…Nitrate reductase inducibility decreased as a result of the pollution treatment, irrespective of the physiological state of the plants. This could be due to accumulation of the NO,," assimilation product, ammonium, or products of ammonium assimilation, inhibiting the enzyme (Woodin & Lee, 1987), although such an effect might not be expected to persist for 4 wk. Another possible explanation of the 4 wk period of decreased nitrate reduction ability is direct damage to the enzyme system resulting from the low pH which accompanies the high N inputs m snow meltwater.…”

“…Acid deposition can also be directly damaging to bryophj'tes. The disappearance of large areas of Sphagnum near the early industrial centres of England was the result of sulphur pollution (Tallis, 1964;Ferguson, Lee & Bell, 1978); growth of Sphagnum there is now inhibited by high N deposition (Press, Woodin & Lee, 1986), and repeated NOg" exposure results in the disruption of N assimilation (Woodin & Lee, 1987). Five years of acid rain treatments to Pleurozium schreberi resulted in reductions in cover, frond height and frond weight (Hutchinson, Dixon & Scott, 1986).…”

Effects of an experimentally applied increase in ammonium on growth and amino‐acid metabolism of Sphagnum cuspidatum Ehrh. ex. Hoffm. from differently polluted areas

“…Anaerobic, waterlogged conditions and acidity combine to restrict mineralization and also nitrification in the peat (Rudolph & Voigt, 1986). In general, mire systems provide negligible nitrate for higher plant growth and ammonium is generally considered the dominant form of nitrogen (Roswall & Granhall, 1980;Dickinson, 1983); virtually all the inorganic nitrogen deposited to the bog surface at unpolluted sites is immobilized by the vegetation, particularly by the bryophyte component (Roswall & Granhall, 1980;Woodin & Lee, 1987). Press & Lee (1982) concluded that Sphagnum species are not adapted to a low ammonium source, but rather to low concentrations of both nitrate and ammonium; high rates oi supply of either oi these ions having the potential to afFect Sphagnum growth adversely.…”

<p><strong>Evaluación briológica de los efectos de la contaminación atmosférica en la Ciudad de México</strong></p>

“…En la Ciudad de México podría esperarse que la lluvia ácida tuviera un efecto negativo en ese fenómeno. Al respecto existen diversos estudios que sugieren que la lluvia ácida puede causar daño a las plantas y cambiar la estructura de las comunidades, pero bajo ciertas condiciones puede actuar como factor estimulante (Rochefort & Dale 1988, Ferguson et al 1988, Woodin & Lee 1987, Winner & Bewley 1983, Kennedy et al 1985.…”