H. Ziegler

Water vapor uptake and photosynthesis of lichens: performance differences in species with green and blue-green algae as phycobionts

SummaryDry lichen thalli were enclosed in gas exchange chambers and treated with an air stream of high relative humidity (96.5 to near 100%) until water potential equilibrium was reached with the surrounding air (i.e., no further increase of weight through water vapor uptake). They were then sprayed with liquid water. The treatment took place in the dark and was interrupted by short periods of light. CO2 exchange during light and dark respiration was monitored continuously. With no exception water uptake in all of the lichen species with green algae as phycobionts lead to reactivation of the photosynthetic metabolism. Further-more, high rates of CO2 assimilation were attained without the application of liquid water. To date 73 species with different types of Chlorophyceae phycobionts have been tested in this and other studies. In contrast, hydration through high air humidity alone failed to stimulate positive net photosynthesis in any of the lichens with blue-green algae (Cyanobacteria). These required liquid water for CO2 assimilation. So far 33 species have been investigated, and all have behaved similarly. These have included gelatinous as well as heteromerous species, most with Nostoc phycobionts but in addition some with three other Cyanophyceae phycobionts. The same phycobiont performance differences existed even within the same genus (e.g. Lobaria, Peltigera) between species pairs containing green or blue-green phycobionts respectively. Free living algae also seem to behave in a similar manner. Carbon isotope ratios of the lichen thalli suggest that a definite ecological difference exists in water status-dependent photosynthesis of species with green and blue-green phycobionts. The underlying biochemical or biophysical mechanisms are not yet understood. Apparently, a fundamental difference in the structure of the two groups of algae is involved.

Hydrogen-isotope composition of leaf water in C3 and C4 plants: its relationship to the hydrogen-isotope composition of dry matter

AbstractThe natural abundance hydrogen-isotope composition of leaf water (

Water status related photosynthesis and carbon isotope discrimination in species of the lichen genusPseudocyphellaria with green or blue-green photobionts and in photosymbiodemes

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Diurnal courses of leaf conductance and transpiration of mistletoes and their hosts in Central Australia

) and leaf organic matter (δDorg) was measured in leaves of C3 and C4 dicotyledons and monocotyledons. The

Effect of sublethal concentrations of zinc, cadmium and mercury on the photosynthetic carbon reduction cycle of Euglena

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Atmospheric Pollutants and Plant Metabolism

value of leaf water showed a marked diurnal variation, greatest enrichment being observed about midday. However, this variation was greater in the more slowly transpiring C4 plants than in C3 plants under comparable environmental conditions. A model based on analogies with a constant feed pan of evaporating water was developed and the difference between C3 and C4 plants expressed in terms of either differences in kinetic enrichment or different leaf morphology. Microclimatic and morphological features of the leaves which may be associated with this factor are discussed. There was no daily excursion in the δDorg value in leaves of either C3 or C4 plants. When δDorg values were referenced to the mean