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.

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Summary. 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.Key words. Exhaust emissions; highway; motor vehicles; Norway spruce; photosynthesis; transpiration.Emissions from motor vehicles are frequently claimed to be major contributors to air pollution, with noxious effects on trees. However, few investigations have been carried out specifically on the toxicity of emissions for trees. Fumigations under controlled conditions were performed by F1/ickiger et al. ~ who demonstrated an inhibition of the regulatory ability of the stomata of Populus tremula leaves. Kammerbauer et al.; studied the impairment of photosynthetic capacity and stomatal regulation in Norway spruce, which was not observed when a catalytic converter was used. Field experiments with grafts of Norway spruce were carried out by Keller 3. Trees kept at roadsides with heavy traffic showed an inhibition of CO2-uptake by 40 % compared to nursery controls after only 13 weeks. At the same time, peroxidase activity was significantly depressed. Visible symptoms such as color changes of the needles could not be observed. We report here an experiment with 6-year-old Norway spruce trees from the same clone which were exposed to roadside conditions for 10 weeks. The control site was essentially free of motor vehicle emissions. A comparison revealed significant differences in growth in length, photosynthetic parameters and transpiration. , six-year-old trees were placed within 5 m of the A 9 motorway (Mfinchen-Nfirnberg) at Allershausen for 10 weeks. The trees were positioned on the eastern side of the road because of prevailing westerly winds. The plants were lowered into the ground in their containers and watered as required. Five controls were kept close to the Department of Botany (Weihenstephan) 15 km from Allershausen under similar conditions except for the relatively unpolluted location with NO x levels amounting to about one tenth of the concentrations observed at the highway. On August 10, 1986, the samples were removed from the highway and left for 1 day in the control area for adaptation. Then the gas exchange parameters (CO2 uptake, dark respiration and transpiration, under different CO; partial pressures at saturating light intensities, i.e. > 1700 pmol quanta m-2s 5) were measured on twigs in an open system (cuvette size: 140 x 80 x 60 mm 3) by means of an infrared gas analyzer as 2 described in detail elsewhere. The needle volume was taken as a reference. It was determined three times as the water displacement of the same twigs used for gas exchange measurements (circa 15 cm length, two needle years) minus the volume of the shoot axes, which was calculated on the basis of measurements with a vernier caliper. The needle area was calculated from the mea...