Gas exchange in cherry leaves infected withBlumeriella jaapii, the causal agent of cherry leaf spot disease, was studied. Infection reduced net photosynthesis during all stages of disease development. Throughout the course of this study there was a continuous decrease in carboxylation and the maximum electron transport rate. Carboxylation was always the most affected parameter, and it seems likely that the infection interferes mainly with the enzymatic processes in the Calvin cycle. There was also a drastic decrease in assimilation, transpiration and stomatal conductance before any visible symptoms occurred on cherry leaves.

Wheat plants were cultivated in a growth chamber at 35 Pa (c(35) variant) and 70 Pa CO2 partial pressure (c(70) variant) during the whole vegetation period. The response of net photosynthetic rate (P-N) Of the nag leaf of both variants to successive increases in CO2 partial pressure (step-up curve) showed hysteresis when the direction of the sequence was reversed (step-down curve) after 1.5 h at saturating CO2 partial pressure and photosynthetically active radiation (PAR). Saccharose, glucose and fructose accumulated during the measurement of a step-up CO2 curve for the c(35) and c(70) plants as the export rate was not able to keep pace with the rate of saccharide synthesis. Remaining 1.5 h at saturating CO2 partial pressure and PAR, the saccharose pool increased further for both variants while glucose and fructose decreased reaching the values at growth conditions. The electron transport rate decreased after 1.5 h at saturating CO2 partial pressure and PAR for the two variants due to end product feedback. Glucose and fructose contents fell 50 % below the initial contents when partial pressure of CO2 was lowered stepwise. The c(35) plants showed a double fold increase in the content of saccharose at the end point of the hysteresis curve. Contents of saccharose for the c(70) variant in contrast were similar to the initial values.

Wheat plants were cultivated in a growth chamber at normal (35 Pa, c35 plants) and enhanced (70 Pa, c70 plants) CO2 partial pressure. In C35 plants the net photosynthetic rate (P(N)) of flag leaves and the concentrations of saccharides such as sucrose, glucose, fructose and starch were increased. The c70 plants possessed higher chlorophyll (Chl) a and Chl b contents. The CO2 response of P(N) at saturating photosynthetically active radiation (PAR) was very similar for both variants. At the highest CO2 concentration saccharides accumulated in both variants as a consequence of decreased export rate. The response of P(N) to PAR at saturating CO2 concentrations was similar in the two variants. On the other hand, the response of water vapour pressure conductance (gH2O) to PAR in c35 plants followed a hyperbolic response to PAR, while in the c70 plants it was linearly related to PAR up to the mean PAR used for growth. In this variant gH2O seemed to change parallelly to changes in the mesophyll demand for CO2 caused by PAR.

The simulation of natural climatic conditions in a modem growth chamber is described. Based on 30 years of meteorological data of the southern Bavarian plain (Donaubecken/Alpenvorland) its typical course of temperature, relative humidity, and photosynthetic active radiation (PAR) was reproduced for a Triticum aestivum culture. While it is possible to simulate successfully the daily course of the temperature, the simulation of the relative humidity is impaired by high transpiration rate of the crop. Light intensity can be simulated realistically.

A method was developed for carrying out gas-exchange and chlorophyll-fluorescence measurements simultaneously during fumigation of spruce twigs with peroxidic photooxidants. It is thus now possible to investigate how a pollutant affects distinct sectors of the photosynthetic apparatus of the plant: whereas fluorescence reveals any changes in the primary light reaction, CO2 gas-exchange measurements supply information about the biochemical reactions of the Calvin cycle. Results of short-time fumigation with 750 ppb ozone are presented here. Gas-exchange and fluorescence data are affected strongly in early summer, but not in autumn. The assimilation rate decreases significantly: primarily as a result of Rubisco activity and possibly because of direct inhibition of the electron-transport chain as well. Closure of the stomata leads to further reduction in the assimilation rate. Though no damage becomes visible on the needles, the perturbance of the photosynthetic apparatus caused by ozone fumigation is not reversible within 24 h.

Four clones of 3-year-old Norway spruce (Picea abies (L.) Karst.), grown on two soils, were from July 1986 to September 1987 exposed to ozone fumigation (50 μg m−3 as a control, 100 μg m−3 plus peaks between 130 and 360 μg m−3 as treatment) and acid mist of pH 3·0 (versus mist pH 5·6 in the control). Climatic conditions, identical for both control and treatment, followed a diurnal and seasonal pattern characteristic of medium high altitudes of the Bavarian Forest, an area affected by the new-type forest decline. Gas-exchange measurements were carried out on the plants from December 1986 until the end of the 14-month's exposure using a series of climate-controlled minicuvettes. ANOVA of the four clones investigated towards the end of the experiment gave hints of a treatment-related depression of the photosynthetic capacity of the previous year's needles (age-class 1986). Within this age-class only one of the clones (11) showed a significant treatment effect, indicating an age-class dependence and a genetic influence of the treatment-related depression of the photosynthetic capacity. The current year's flush was not impaired through the ozone and acid mist exposure. Analysis also revealed clear effects of soil, clone and needle age on photosynthetic parameters.

In the present paper, we address the question whether the injuries of acute toxic concentrations of exhaust emissions are due to systemic effects or are rather the result of localized and direct effects upon the needles. Twigs from exposed spruce trees, which had been prevented from contact with the exhaust emissions, did not show any decrease of photosynthetic or transpiration rates within four weeks. Chlorophyll fluorescence was also not affected in these parts, while it was severely impaired in the exposed twigs.

Peroxides are thought to be among the causes of forest decline (1). Therefore the effect of fumigation with several peroxides on the photosynthesis of spruce needles (picea abies) was studied.

This contribution tries to answer some questions on the characteristics of ear photosynthesis:

Six-year-old Norway spruce trees of the same clone were exposed for 10 weeks at the edge of a highway and compared with controls kept in an unpolluted area within 15 km of the first site. Significant differences could be observed with respect to growth, photosynthesis and transpiration rate, all of which were reduced after exposure at the highway.

Six-year-old Norway spruce trees were exposed for 30 min under standardised conditions to the exhaust from an Otto engine running on lead-free petrol. Gas-exchange measurements in an open system using an infrared gas analyser showed a sudden, severe drop in CO(2) assimilation and transpiration rates. By using filters which absorbed different fractions of the exhaust it could be demonstrated that the toxic effects can be attributed to the NO(x) fraction.

Exhaust emissions from automobiles have been frequently connected with a new type of forest disease which is described for conifers and, more recently, also for deciduous trees. The use of the catalytic converter for pollution control and, consequently, as a remedy for forest decline, has been extensively advocated. No data are yet available on the efficiency of catalytic devices with respect to the toxicity of exhaust emissions. We have therefore studied this question in Norway spruce Picea abies (L.) Karst. under defined conditions. The efficiency of the catalyst was tested with concentrations of exhaust emissions which produced significant injuries within a limited period of time. A fast reduction of photosynthetic capacity and impairment of stomatal regulation was observed after a fumigation of only 15 min without a catalytic converter, followed by changes in colour and, finally, by needle dropping. During the early stages, buds were not injured and developed into healthy shoots. Consequently, symptoms of an inner browning and needle dropping could be mimicked. In the presence of a catalytic converter, essentially no damage to spruce could be observed under analogous conditions.

Mit Hilfe von Licht- und CO2-Sättigungskurven läßt sich ein quantitatives Maß für physiologische Veränderungen infolge Schadstoffexpositionen und unterschiedlicher Ernährung gewinnen. Es konnten Veränderungen im Photosynthese- und stomatären Apparat unterschiedlicher Ausprägung je nach Schadstoffvariante beobachtet werden. Insbesondere sind die Photosyntheseleistung und die stomatäre Regulationsfähigkeit bei ozonbegasten, nichtgedüngten Pflanzen herabgesetzt und die Kompensationspunkte für CO2 und Licht stark erhöht. Durch Düngung mit Mg und Ca erhöht sich die Photosyntheseleistung.

The CO2‐ and H2O‐exchanges in the flag leaf and the ear of a spring wheat cultivar (Triticum aestivum L. cv. Arkas) were measured at CO2 partial pressures, pi(CO2), between 8 and 400 Pa under high photosynthetic photon flux densities (2000 μmol m−2 s−1). The experiments were carried out on each organ separately while attached to the intact plant, from the time of ear emergence through senescence. To study the contribution of the kernels to the gas exchange of ears, experiments were also carried out on sterilized ears (treatment A), and on ears from which the kernels were removed (treatment B).Flag leaves and ears differed considerably with regard to CO2‐dependence of assimilation, response of stomata to varying pa(CO2), CO2 compensation point (and its temperature dependence), dark respiration, and dissimilation in the light (i.e. CO2 production which is not due to oxygenation of ribulose 1,5‐bisphosphate). The higher dark respiration of the ear originated mainly from the kernels and continued to some extent in the light. Thus, the CO2 compensation point was attained at higher CO2 partial pressures for the ear than for the flag leaf.The CO2 uptake of the ear was not saturated at intercellular CO2 partial pressures below 180 Pa CO2, while that of the flag leaf reached saturation at about 80 Pa CO2. CO2‐saturated rates of CO2 uptake were 2.5 and 1.5 times the rates at natural CO2 partial pressure for ear and flag leaf, respectively. The stomatal conductance decreased with rising CO2 partial pressure above 35 Pa, in a more pronounced manner for the flag leaf than for the ear.