Impact of gaseous nitrogen deposition on plant functioning

Abstract

 Dry deposition of NH$ and NO x (NO and NO # ) can affect plant metabolism at the cellular and whole-plant level. Gaseous pollutants enter the plant mainly through the stomata, and once in the apoplast NH $ dissolves to form NH % + , whereas NO # dissolves to form NO $ − and NO # − . The latter compound can also be formed after exposure to NO. There is evidence that NH $ -N and NO x -N can be reversibly stored in the apoplast. Temporary storage might affect processes such as absorption rate, assimilation and re-emission. Once formed, NO $ − and NO # − can be reduced, and NH % + can be assimilated via the normal enzymatic pathways, nitrate reductase (NR), nitrite reductase and the glutamine synthetase\glutamate synthase (GS\GOGAT) cycle. Fumigation with low concentrations of atmospheric NH $ increases in vitro glutamine synthetase activity, but whether this involves both or only one of the GS isoforms is still an open question. There seems to be no correlation between fumigation with low concentrations of NH $ and in vitro GDH activity. The contribution of atmospheric NH $ and NO # deposition to the N budget of the whole plant has been calculated for various atmospheric pollutant concentrations and relative growth rates (s). It is concluded that at current ambient atmospheric N concentrations the direct impact of gaseous N uptake by foliage on plant growth is generally small. Key words : Apoplastic storage, gaseous nitrogen deposition, glutamate dehydrogenase, glutamine synthetase, plant nitrogen demand, sulphur dioxide root\shoot interaction, ammonia, nitrogen oxides. Anthropogenic emissions of nitrogen-containing air pollutants far exceed natural emissions in Europe and North America. These emissions cause two types of effect : generation of tropospheric O $ , and excess N deposition, which can result in direct phytotoxic effects, eutrophication, acidification and stimulation of greenhouse gas production. Anthropogenic emissions of N-containing air pollutants have resulted in atmospheric N deposition 5-20 times higher than in natural conditions. Indications of N excess in the field can be seen from : (1) changes in the species composition of indigenous vegetation types, with an increase in nitrophilous species and a decrease in others, and (2) increases in foliar N * To whom correspondence should be addressed. E-mail : g.stulen!biol.rug.nl. Abbreviations : GDH, glutamate dehydrogenase ; GS, glutamine synthetase ; GOGAT, glutamate synthase ; , net nitrate uptake rate ; NR, nitrate reductase ; P95, 95 percentile ; , plant nitrogen content ; , relative growth rate.

Ecological ramifications of the direct foliar uptake of nitrogen

“…, respectively (Zeevaart 1976;Wellburn 1990;Gessler and Rennenberg 1998). The NO/NO 2 reaction is irreversible and dependent upon the concentration of NO 2 -/NO 3 -in the apoplastic solution (Remmler and Campbell 1986;Stulen et al 1998). The dissolution of NH 3 into the leaf apoplast is driven by the gradient in concentration between the NH 3 concentration in the air of the substomatal space and the surrounding mesophyll tissue.…”

“…The other major source of NH 3 in the cytosol is photorespiratory and, as such, the NH 3 derived from foliar uptake interacts directly with photorespiratory processes. Glutamate dehydrogenase has also been suggested as an alternative to the GS/GOGAT system (Srivastava and Singh 1987;Stulen et al 1998), but appears to play a minor role in the assimilation of atmospheric NH 3 (Rhodes et al 1989;Krupa 2003). GS is often found in plants as two isoforms, one cytosolic and the other chloroplastic (Fig.…”

NH3 and NO2 fluxes between beech trees and the atmosphere – correlation with climatic and physiological parameters

“…Since the residence time of NO # in the atmosphere is longer than that of NH $ , the spatial variability of NO # concentration is much lower. Therefore NO # produced in the urban environment is also an important contributor to the atmospheric N load of rural ecosystems, at least in central Europe, where population, traffic density and diversity of land use within a small area are generally high (Stulen et al, 1998).…”

“…A prerequisite for the emission of NO # at low atmospheric concentrations is the presence of NO # in the gaseous phase inside the leaves. Stulen et al (1998) proposed that NO x -N taken up from the atmosphere is stored reversibly, especially as nitrate and\or nitrite, in the apoplast. Since the beech trees at the field site are exposed to considerable amounts of NO # (annual mean in 1995 approx.…”

“…Ammonium, NO $ − and\or NO # − dissolved in the apoplast can be taken up into the mesophyll cells and assimilated, and might contribute to the N supply of the whole tree (Wellburn, 1990). Trees supplied with additional N from the atmosphere might react with additional growth and\or N storage (Stulen et al, 1998), or might adapt pedospheric N uptake from the soil to their requirements, depending on their nutritional state (Imsande & Touraine, 1994 ;Muller et al, 1996 ;Geßler et al, 1998b).…”