Aci d addition did not result in a signi fi cant inc rease in the amount of K present in the soi l soluti�n , i . e . there was negligible exchange with H i ons . Ca was the maj o r cation exchanged following acid addition. Howeve r, when the proportions of exchanged Ca and Mg out of total exchangeable Ca and Mg we re calculated, i t was apparent that a highe r proportion of the Mg had exchanged wi th H ions than that of Ca. No exchange of Fe was detected in the humus wi th the acid additions used he re, and Al was only released afte r the pH fell below 3. The cri ti
cal pH for Al d i ssolution in the mine ral soi l was around 4, and that for Fe a round 3.5. The affini ty of the cations for exchange sites was determined by calculating the ratio:
extract-400
able cation (i.e. f ree in soil solution)/ total exchangeable cation (i.e. bound on exchange sites ) . The affinity of the cations followed the orde r : K < Mg < Mn < Ca < Al < Fe .
t:'oN'CWSIOHS
When we consid�r tllle possil>le illll!)act of �cidic aeposition elm F:iJ:lil'lish forest soils f:,:-om the po!i.nt of view of the supply of lrlu1:ri-ts t,9 :th�
stMNi, it -w-oui"d appear that .one .po$$;i..b;Le p�ob
lem could be losses of Mg thr0111.gh acli,d�indllC�
cat.ion exchange� Al't:hou'lfh gaantitatively �ealc
ing Ca exchange is much greater, a higher pro
portion o-f the excllclngeable Mg, is lost follow
ing acid addition. Such Mg shortages are, h9W�
ever, likely to be fdirly shart-lived bec��;r.e the mineral soil contains very large re�rv�
of "easily wea.th.n-at>le" •aqnesi1.ll!l. If. ·acip.
depositian continues at a constant , hea:vy .l�vr
el , however, then these reserves may not be
come available at a sufficiently fast rate to counteract the losses of available Mg. This is one possible explanation for the needle discol
ouration, assumed to be due to a Mg deficiency, that was observed over extensive areas in Fin
land following the exceedingly cool and wet summer of 1987.
Although K has a very low affinity for cation exchange sites , acid-induced K exchange is insignificant owing to the fact that most of the K is already free in soil solution under the pH conditions prevailing in Finnish forest soils .
It is difficult to exchange or liberate the aluminium from the exchange sites or organic aluminium complexes in the humus layer, as well as in the A horizon of the mineral soil. In the humus Al was not released into solution until the pH fel l below 3 . Aluminium hydrox
ides in the B horizon, on the other hand, were dissolved when the pH fell to around 4 .
Air Pollution and Forest Decline (J. B. Bucher and I . Bucher-Wallin, eds.) .
Proc. 14th Int. Meeting for Specialists in Air Pollution Effects on Forest Ecosystems, IUFRO P2. 05, Interlaken, Switzerland, Oct . 2-8, 1988. Birmensdorf, 1989, p. 401-403.
EFFECTS OF N02 ON ASSIMILATORY NITRATE- AND SULFATE REDUCTION IN NEEDLES FROM SPRUCE TREES (PICEA ABIES L.) .
Egger A., Landolt W.* & Brunold Ch.
Pflanzenphysiologisches Institut, Universitat Bern, CH-3013 Bern, Switzerland.
*Eidg. Anstalt fur das Forstliche Versuchswesen CH-8903 Birmensdorf, Switzerland
ABSTRACT
This poster presents a choice of results from experiments done in the years 1985 to 1987 about the influence of N02 on the extractable activities of nitrate reductase (NR) , nitrite reductase (NiR) , adenosine 5 ' -phosphosulfate sulfotransferase (APSSTase) and the content of free amino acids in needles from spruce trees. Three or five years old potted clones were exposed in open-top chambers or nearby a highway with a control in a rural region with low air pollution. During the aeration experiments the N02 concentrations were 100 and 150 ,ug/m3 respectively. The N02 conclntration near the highway was about �9 ,ug/m and at the control site about 12 ,ug/m . The open-top chamber experiments showed that No2 in the concentrations used caused a significantly increased extractable NR- and NiR-activity in the needles. The activity of the APSSTase measured was not significantly influenced. Similar effects were observed in the trees near the highway . The differences were detected during the first 24 or 48 hours of exposure and were always reversible.
The amino acid contents were not significantly affected after the exposure.
In an experiment with a longer exposure we got some indications that in presence of higher N02 concentrations the total amino acid content slightly increased.
Further experiments will show, whether and in what rated by spruce needles. quantity the N02-nitrogen is incorpo
INTRODUCTION
The air pollutant N02 especionally along with so2 and o3 occasionally leads to detectable direct and indirect damages to plants (Guderian, 198 5 ; Lank, 1985) . Beside these effects, N02 can act in acidification, as a precursor of photochemical oxidants and as a potential nitrogen source. This last possibility was the main object of the work presented here. We wanted to know, if relevant parts of physiological pathways in needles of Spruce trees (Picea abies L.) respond to a gaseous nitrogen source in the form of N02 ? Several papers reported on different direct and indirect effects on various plant Srivastava ( 1984 ) species found, that the of N02 • NR activity in bean leaves was increased by N02 and that this effect was much higher during a perioid of a limiting N supply. An incorporation of the N02-N was also documented (Matsumaru, 1979 ; Srivastava, 1984 ; Johansson, 1987) . The
activity of NiR, the second step of the assimilatory N-reduction, may be also influenced by gaseous application of N02 (Wellburn, 1981) . Further it was shown by many authors (Yang, 1983; Freer-Smith, 1984 ; Wright, 1987 ; Wellburn, 198 1 ; ECE report, 1988) that N02 alone effects less aggravating than so2 and o3 alone or in any combination also with N0,2. It is well known, that there are essential differences among plant species, treated with the mentioned pollutants, especially relative to the stomata! aperture (Landolt and Keller, 1985 ; Lendzian, 1983) , which is the most important precondition for a relevant uptake of N02 during pollution episodes (Saxe, 1986) . If enzymes of the N-reduction were influenced by N02, we can suppose that an unknown amount of the gas was incorporated. Provided that a higher in vitro NR- and NiR-activity is linked with an increased N-assimilation in vivo, we have reasons to think, that also the s-assimilation is influenced (Suter et al., 1986) and furthermore the pools of free amino acids and protein•.
ABBREVIATIONS NR NiR
APSSTase
RESULTS
nitrate reductase nitrite reductase
adenosine 5 ' -phosphosulfate sulfotransferase
Figures 1-3 and table 1 show results of the fumigation- and exposition experiments. More details are presented as footnotes under the illustrations. All experiments were repeated at least four times. Means and standard deviations were calculated from five or eight values. Statistical analysis was performed according the Duncan' s multiple range test.
*
P � 5% ; ** P � 1% ; *** P � 0.1%.I C NiR activity increased significantly also.
The key enzyme of the assimilatory sulfur reduction (APSSTase) didn't show significant differences to the control with filtered air.
Table 1: The results of the amino acid analysis from needles of the exposed spruce trees are tabulated above as n mol/g fresh weight . After ten days near the highway no relevant difference could be detected compared with the control.
control hiCJhv•y control highway
to to t1.o t10
Figure 3: The exposition of spruce trees near a highway demonstrated an increasing of the NR activity in the needles. After 10 days (arrows) the control trees were exchanged with that near the highway. In consequence the NR activity followed the new treatment.
DISCUSSION AND CONCLUSIONS
An enhanced N04 concentration leads under controlled conditions and in open-air experiments to increased activities of the NR and NiR in the needles of spruce trees.
The APSSTase activity (the key enzyme of the assimilatory sulfate reduction) wasn' t significantly influenced during these short
time experiments.
After a ten days exposition near a highway the N-assimilation was obviously influenced. A difference of the amino content in the needles couldn' t be detected after this short time. After a similar experiment over a longer period of time, a higher amino acid content' was indicated.
With this results we can suppose that an unknown amount of the N02-N was incorporated. In the presence of a higher N02 concentration over a longer time, we have reasons to think, that also the s-assimilation is changed and furhermore the pools of free amino acids and proteins.
Further experiments will show in what quantity plants incorporate the N02-N, how relevant this air pollutant act as a nitrogen source and if it probably changes the society of plant species in an ecosystem.
REFERENCES
Blank, L. W., & Roberts, T. M. 1985. Response of Sitka spruce to long-term fumigation with realistic mixtures of so2, N02 and ozone. -In VDI-Berichte. Nr. 560: 717-724.
ECE Final Draft Report. 1988. - ECE Critical Levels Workshop, Bad Harzburg, FRG. pp 79-104.
Guderian, R., Kuppers, K. & Six, R. 1985.
Effects of o3, so2 and N02 on spruce and poplar supplied with various rates of Mg and Ca, and on the lichen Hypogymnia physodes. -In VDI-Berichte. Nr. 560: 657-701.
Freer-Smith, P. H. 1984. The responses of 6 broad-leaved trees during long-term exposure to sulfur dioxide and nitrogen dioxide. - New Phytologist 97: 49-62.
Johansson,
c.
1987. Pine forest a negligible sink for atmospheric nitrogen oxides in rural Sweden. Tellus ser. B. Chem. Phys.Meteorol. 39: 426-438.
Saxe, H. 1986. Stomatal-dependent and stomatal-independent uptake of N02. New Phytol. 106: 199-205.
Suter, M., Lavanchy, P., Von Arb, c. &
Brunold,
c.
1986. Regulation of sulfate assimilation by amino acids in Lemna minor L.- Plant Science 44: 125-132.
Srivastava, H. S. & Ormrod, Effects of nitrogen dioxide nutrition on growth and nitrate in bean leaves. - Plant Physiol.
D. P. 1984.
and nitrate assimilation 76: 4 18-423.
Wellburn, A. R., Higginson, c., Robinson, D.
, Walmsley,
c.
1981. Biochemical explanations of more than additive inhibitory effects of low atmospheric levels of sulphur dioxide plus nitrogen dioxide upon plants. - New Phytol. 88: 223-237.Wingsle, G., Nasholm, T., Lundmark, T. &
Ericson, A. 1987. Induction of nitrate reductase in needles of Scots pine seedlings by NOx and N03 - • - Physiol. Plantarum 70: 399-403.
Air Pollution and Forest Decline ( J.B. Bucher and I. Bucher-Wallin, eds.).
Proc. 1 4th Int. Meeting for Specialists in Air Pollution Effects on Forest Ecosystems, IUFRO P2.0S , Interlaken, Switzerland, Oct. 2-8, 1 988. Birmensdorf, 1 989, p. 404-406.
IMMISSIONSOEKOLOGISCHE UNTERSUCHUNGEN AM WALD IM KANTON ZUERICH L. Fordererl,3, J. Thudiuml, P. Bucherl,4, M. Knecht2, R. Huber2,
L. Kellerl und W. Fliickiger3. 1 okoscience, Quellenstrasse 25, 8005 Ziirich
2 Ambio, Seefeldstrasse 120, 8008 Ziirich
3 lnstitut fiir angewandte Pflanzenbiologie, Sandgrubenstrasse 25, 4124, Schonenbuch.
4 Anorganisch chemisches lnstitut der Universitlit Ziirich.
ZUSAMMENFASSUNG
An 13 Standorten im Kanton Ziirich wurden zwischen 1984 und