SUMMARYThe effect of ozone on the yield, yield components and grain composition of spring wheat {Triticum aestivum L., cv. Albis) was investigated in 1989 and 1990 at 900 m above sea level. Plants were grown from the three-leaf stage until harvest in open-top chambers ventilated with charcoal-filtered air (CF), unfiltered air (UF) or unfiltered air with one of two levels of O3 added when global radiation exceeded 400 J m"^ s'^ (O3-I, O3 -2). Ambient plots (AA) without chambers were used as a reference. Mean 7-h d ' (09.00-16.00 h) O3 concentrations in the CF, O3 -1 and O3 -2 treatment, respectively, was approximately 05, 14 and 18 times the concentration in the UF treatment, which was 70 /(g m"^ in 1989 and 76 //g m"^ in 1990. The OTC environment was characterized by a warmer, more humid microclimate and reduced soil moisture, compared with the open field. In 1989, this eflFect of the chambers was more pronounced than in 1990. When compared with AA plots, chamber enclosure significantly reduced grain and straw yield in 1989, while in 1990 no difference was observed. Grain yield decreased with increasing seasonal mean O3 concentration as a result of reductions in the weight of individual grains and in the number of grains per head. A small decrease in the ratio between grain weight and total above-ground biomass (harvest index) indicated a shift in biomass allocation. With increasing O3, small or no changes were observed in protein, starch and K concentrations, and in protein quality (Zeleny value) of the grain. Relationships between different measures of O3 exposure and relative grain yield were constructed with a quadratic model. With mean concentrations (7-h d^' mean or radiation-weighted mean) or with a cumulative index (SUMO6 = sum of concentrations above 60 //I 1"') to describe exposure, the response of grain yield to increasing O was smaller in 1990 than m 1989. Nearly identical exposure-response functions were obtained for both seasons, with the mean O3 flux used to estimate the absorbed dose of O3. Quadratic exposure-response functions suggest that ambient levels of O3 reduced grain yield by 95 "o and 11 6",, in 1989 and 1990, respectively. Using Weibull exposure-response functions, a comparison with results from an earlier study at 485 m above sea level indicates reduced sensitivity at the higher elevation.

SUMMARYSpring wheat {Triticum aestivum L., cv. Albis) was grown in open-top chambers and exposed to four different levels of ozone (O,,) from the three-leaf stage until maturity. The aim was to examine changes in leaf and canopy gas exchange, and in chlorophyll fluorescence, in response to O3 flux. Measurements were carried out periodically between full expansion and complete senescence of flag leaves. Fluxes to the canopy of CO^ (CER^O (corrected for soilborne CO^), water vapour (E^) and O,, were determined by using open-top chambers as differential systems. Water use efficiency (WUE,.) was calculated from CER, and E,. Leaf CO., (CERJ and U.p (EJ exchange rates, stomatal conductance (^.(H^O)), and WUE,,, were analyzed with a portable gas exchange analyzer. Effects of O3 flux on structural components of photosynthesis were examined by determining variable fluorescence (defined by the F^./E,^ ratio) in leaves after 60 minutes of dark-adaptation or during the night.The decline in CER,. and CER,, associated with senescence was accelerated by O3. Average CER,, between flag leaf unfolding and late milk stage declined linearly with increasing O3 flux. The corresponding decline in average CER,. was less pronounced. The quantitative effect of O, flux on CER^, corresponded well with the effect on grain yield. In young leaves, g,(H.p) was reduced in response to O.j but WUE^ was unaffected. With progressing leaf age, WUE^ declined. Thus, in the young leaves, O., affected the stomata directly and, consequently, limitation of photosynthesis was primarily due to reduced CO., diffusion. In contrast, in senescent leaves, the effect of O3 was mainly due to reduced carboxylation. Compared with WUE,,, WUE,. responded differently to increasing O,, flux. During O3 fluxes at above-ambient levels, WUE,, tended to increase rather than to decrease. It is suggested that under O3 stress, factors controlling WUE at the canopy level differ from those operating at the level of single flag leaves. The decline in F JF,, measured after anthesis was stimulated by O3, but no effect of O3 was detected when FJF,, was measured during the night. This leads to the conclusion that the effect of O3 on photosynthetic structures is reversible and the reduction in photosynthesis in response to O3 flux is due to metabolic changes rather than to direct damage to structural components.

summary The flux of O3 was determined in open‐top chambers (OTC) used to investigate its effect on spring wheat (Triticum aestivum L., cv. Albis) in 1989 and 1990. The experimental site was located at 900 m above sea level at Zimmerwald, near Bern (Switzerland). The aims were to evaluate the use of OTCs for O3 flux measurements under field conditions, to assess the role of stomata in controlling the O3 fluxes, and to establish a quantitative relationship between radiation‐weighted O3 concentrations and O3 flux. Measurements were carried out from full expansion of flag leaves until the onset of senescence. Ozone flux was determined by mass balance using the concentrations of O3 measured at the inlet and outlet of the OTC. The CO2 exchange rate was corrected for soil‐borne COO and used as a reference. Measurements of temperature, photosynthetically active radiation (PAR), saturated water vapour pressure deficit (SVPD), and boundary layer conductance were used to describe the microclimate inside OTCs. In the warmer microclimate in 1989, the plant canopy was characterized by a smaller leaf area index (LAI) than in 1990, while the fluxes of O3 and CO2 during daytime were generally larger in 1989. The diurnal patterns of fluxes of O2 and CO2, in OTCs supplied with unfiltered air were similar. It is estimated that O3 absorption via the stomata contributed 50–70% of its total flux. Identical relationships between leaf conductance for O2, measured by porometry and leaf conductance calculated from O3 flux were found in both years, but measured leaf conductance during daytime was generally smaller in 1990 than in 1989. The results indicate that stomatal conductance largely controlled O3 flux, and that the canopy structure has an influence on the overall conductance of the canopy. Different linear functions were obtained for the relationship between radiation‐weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal‐filtered air, unfiltered air or unfiltered air enriched with O. (two levels). These relationships form the basis for the calculation of mean O3 fluxes which can be used as an exposure index in the exposure‐response analysis.

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In der vorhergehenden Abhandlung l) hat der eine ~o n uns zu den bis daliin vorliegenden Berichten iiber die Entdeckung des Elemente;. Nr. 61 durch J. A. H a rr i s , L. F. Y n t e m a und B. S. H o p k i n s Stellung genommen. Seine Meinung war, dai3 die Beobchtungen in1 Bogen-und im Absorptionsspektrum keine Beweise fiir das Vorhandensein des Elementes sind, und daD die daiiials vorliegenden rontgenspektrographischen Angaben zu unvollstandig und nicht klar genug waren, als dai3 sie uberzeugend wirkten. Nunmehr haben die Genannten in zwei weiteren Abhandlungen z, ausfuhrlicher iiber ihre Untersuchungen berichtet. In bezug auf die erste dieser beiden Abhandlungen, die den optiniistischen Titel ,,Element Nr. 61. Concentration and isolation in impure state" tra@, ist deni fruher Gesagten nichts mehr hinzuzufiigen. Die zweite Xbhandlung dagegen enthalt die bisher vermiaten genaueren Angaben iiber die Rontgenanalyse. Zu dieseii wollen wir heute Stellung nehmen. H a r r i s , Y n t e m a und H o p k i n s haben eineu Kontgenspektrographen von dem uas bisher nicht bekannten Uhler-Typ verwendget. Aus den Angaben uber ihn geht hervor, daD er ein gasgefulltes Rontgenrohr mit Aluminiumkathode und gekiihlter Kupferantikathode besitzt, und dai3 der Spektrograph nicht evakuiert ist. Als Drehkristall dient Calcit. Der Abstand zwischen den1 Ypalt, iiber dessen Breite und Abfstand von der Antikathode lteine Angaben gemacht sind, und den1 Drehkristall und folglich auch der von letzterem zum Plattenhalter betrug bei den beiden ersten Aufnahmen 15,41 cm, bei den folgenden wurde er mit Rucksicht auf die starke Luftabsorption auf 8,81 cm verkiirzt. Fur diesen letzteren Abstand lai3t sich die Dispersion dea Apparates zu 0,03 mm pro X-Einheit berechnen. Der von H a r r i s , Y n t e m a und H o p k i n s angegebene Wert von 0,5 min fur den Abstand zwischen der La,-und La,-Linie des Samariums gilt nur fur den anfanglich verwendeten groi3eren Plattenabstand. Die Spannung betrug im Mittel 30000 Volt, die Stromstarke im Mittel 8-10 Milliampere. Es wurde nur das L-Spektrum aufgenommen. Die Schwenkung des Kristalls betrug nur einen Winkel von 30 Minuten, d. h. es wurde mit einem fast stehenden Kristall gearbeitet. Der aufgenommene Spektralblereich umfaDte unter diesen Urnstanden nur etwa den Abstand der La,-Linien benachbarter Erdelemente der Ordnungszahlen 58-62, d. h. hochstens 0,1 oder 100 X-Einheiten. Mit Rucksicht auf die starke Absorption der Strahlung durch die Luft m a t e sehr lange exponiert werden; die Expositionszeiten betrugen zwischen lo1) und 24l/, Stunden. Da pulverformige Erdoxyde wahrend so langer Expositionszeiten von der Antikathode verstaubt werden, wurden die Proben in einer Vertiefung der auf die Antikathode gebrachten Kupferplatte im elektrischen Lichtbogen geschmolzen, wobei die Kupferplatte als die eine, ein Kupferstab als die andere Elektrode diente. Der so erhaltene Knopf van geschmolzenem Erdoxyd sol1 merkwurdigerweise vollig kupferfrei gewesen lsein und bei der Verwendung als Antikathode auch bei langer Expositi...