Consequences of high loads of nitrogen for spruce (Picea abies) and beech (Fagus sylvatica) forests

Abstract

High loads of nitrogen to spruce and beech forests can result in a complete inhibition of NO $ − uptake by the roots of the trees. This conclusion is based on (a) a comparison of a field site continuously exposed to high loads of N and a N-limited site, (b) the results of N fertilization of a N-limited field site, and (c) laboratory experiments under controlled environmental conditions. From fertilization experiments in the field it appears that NH % + uptake might become inhibited subsequent to an excessive uptake of NH % + . Apparently, the inhibition of NO $ − uptake by high loads of N to forests is a consequence of an accumulation of organic amino compounds in the roots originating from phloem transport from the shoot to the roots. These amino compounds seem to signal the N demand of the shoot to the roots. At present this function cannot be attributed to an individual organic amino compound in beech or spruce, but Gln is a likely candidate in both species among other compounds, e.g. Glu in spruce or Asp in beech trees. Direct inhibition of NO $ − uptake by NH % + can be excluded from the present studies. The mechanism(s) by which elevated levels of particular organic amino compounds interact with NO $ − uptake remains to be elucidated. This (these) mechanism(s) seem to affect NO $ − influx rather than NO $ − efflux. As a consequence of this (these) mechanism(s), spruce and beech trees can prevent, within a certain physiological window, N over-nutrition when the roots are exposed to excessive amounts of inorganic N. However, inhibition of NO $ − and NH % + uptake by the roots makes more N available for leaching into the ground water and, in addition, for soil microbial processes that result in the production and re-emission of volatile N compounds into the atmosphere.At the ' Ho$ glwald ' site, continuously exposed to high loads of N, 20 % of the N input from throughfall into the spruce and beech plots is re-emitted as NO and N # O. However, the NO to N # O ratio is highly dependent on the tree species, with a preference for NO in the spruce and a preference for N # O in the beech plot. Since at least part of the NO emitted from the soil will be converted inside the canopy in the presence of ozone to NO # that might then be absorbed by the leaves, the portion of the N in the throughfall that will be released from the forest by gaseous N emission is higher in the beech than in the spruce plot. Leaching of NO $ − into the ground water is high in the spruce, but minute in the beech plot. However, this positive effect of beech on ground water quality is achieved at the expense of an enhanced release of radiatively active N gases into the troposphere.Key words : Atmospheric pollution, forest ecosystem, nitrogen allocation, nitrogen fluxes, regulation, nitrogen oxides, ammonia. Both atmospheric and pedospheric sources of nitrogen are available to plants. The contribution of atmospheric N is considered to be low in remote * To whom correspondence should be addressed E-mail : here!sun2.ruf.uni-fre...

Impacts of tropospheric ozone and airborne nitrogenous pollutants on natural and semi‐natural ecosystems: a commentary

“…Most research has, however, focused on forestry stands and on the effects on trees (see Pearson & Stewart (1993), Fangmeier et al (1994) and Rennenberg et al (1998), for reviews). As indicated above, the impacts of increased atmopheric nitrogen deposition upon natural and semi-natural ecosystems are too diverse for a full discussion here ; more detailed information is provided by Bobbink, Hornung & Roelefs (1998), Aerts & Bobbink (1998) and Lee & Caporn (1998).…”

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

“…The ranges of NH $ and NO # concentrations were c. 0n4-240 (Geßler & Rennenberg, 1998) and 0n02-44 nmol mol −" (R. Gasche & H. Papen, unpublished), respectively. A detailed site description is given by Rennenberg et al (1998).…”

Interactions between leaf nitrogen status and longevity in relation to N cycling in three contrasting European forest canopies

“…Due to deposition of atmospheric NH 3 , the critical N load for European forest ecosystems is often exceeded Pinho et al, 2012). This may in turn lead to elevated concentrations of NH + 4 and organic N compounds in the trees and to NH 3 emission events (Rennenberg et al, 1998;Fowler et al, 2009). The physiological…”

“…Nitrogen (N) fluxes and turnover in forests are therefore relevant for biogeochemical cycling of N in Europe . Forest ecosystems are generally considered to be adapted to N limitation rather than to N excess (Vitousek and Howarth, 1991;Rennenberg et al, 1998;Aerts, 1996;Xia and Wan, 2008). Due to deposition of atmospheric NH 3 , the critical N load for European forest ecosystems is often exceeded Pinho et al, 2012).…”