Assessing the impact of ozone on photosynthesis of European beech (Fergus sylvatica L.) in environmental chambers

An exposure — response study with proportionalto-ambient ozone levels was conducted in closed chambers on 3-year-old European beech (Fagus sylvatica L.) of montane origin. The fumigation started in April 1990 and lasted for a single growing season. Climate data and ozone concentrations monitored at an experimental station of the Institute for Applied Plant Biology, Schönenbuch, Switzerland were simulated in the exposure chambers 12 days later (1*O₃). To test exposure-response relations three additional treatments were applied, subambient (0.2*O₃) and two proportionally increased ozone treatments (1.5*O₃ and 2*O₃). The photosynthetic behaviour of the trees in August revealed the light reactions to be less affected than parameters which are related to the dark reactions of photosynthesis. Assimilation (A₃₅₀), apparent carboxylation efficiency (CE), and maximum photosynthetic capacity (A₂₅₀₀) were reduced with increasing ozone concentration. For the ozone response of CE and A₂₅₀₀ Critical Levels were calculated.     

A simple model of human foveal ganglion cell responses to hyperacuity stimuli

We developed a physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina. With the predictions of this model we could support the hypothesis that, for moderate contrasts ( 40%), hyperacuity is mediated by the magnocellular (MC-) pathway. Despite the lower sampling density in the MC pathway, as compared to the parvocellular (PC-) pathway, the information that is transferred by the MC ganglion cells is sufficient to achieve thresholds comparable to those of human subjects in psychophysical tasks. This is a result of the much higher signal-to-noise ratio of the MC pathway cell signals. The PC pathway cells do not transfer enough information for hyperacuity thresholds.     

Seasonal metabolism of a small, arboreal monitor lizard, Varanus scalaris, in tropical Australia

The field metabolic rates (FMR) and water fluxes of Varanus scalaris were measured during the wet and dry seasons by the doubly-labelled water technique. Seasonal measurements of standard (night-time) metabolism (SMR) and resting (daytime) metabolism (RMR) were made in the laboratory at 18, 24, 30 and 36°C, and maximal oxygen consumption was measured at 36°C on a motorized treadmill. This population was active throughout the year. In the wet season, the mean FMR was 7.8 kJ day⁻¹ (128.0 kJkg⁻¹ day⁻¹; mean mass = 66.4 g, n = 13), and during the dry season the mean was 5.0 kJ day⁻¹ (67.6 kJ kg⁻¹ day⁻¹; mean mass = 77.4 g, n = 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day⁻¹, respectively (60.4 and 16.6 ml kg⁻¹ day⁻¹). The seasonal means of FMR and water flux were significantly different by ANCOVA ( P < 0.0001). Measurements of SMR and RMR were significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P = 0.6). The maximal oxygen consumption of the lizards on the treadmill (2.9 ml min⁻¹= 1.8 ml g⁻¹ h⁻¹), mean mass = 97.4 g, n = 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. The seasonal differences in FMR were attributable to: changes in SMR (12.2%) and RMR (16.4%); differences in night-time body temperatures (11.3) and daytime body temperatures (16.4%); and activity (broadly defined to include locomotion, digestion, and reproductive costs (43.7%).