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  • 1
    Electronic Resource
    Electronic Resource
    Water status related photosynthesis and carbon isotope discrimination in species of the lichen genusPseudocyphellaria with green or blue-green photobionts and in photosymbiodemes (1988)
    Springer
    Oecologia 75 (1988), S. 494-501 
    Details
    ISSN: 1432-1939
    Keywords: Photosymbiodeme ; Phycosymbiodeme ; Delta13C ; Lichen ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Green lichens have been shown to attain positive net photosynthesis in the presence of water vapour while blue-green lichens require liquid water (Lange et al. 1986). This behaviour is confirmed not only for species with differing photobionts in the genusPseudocyphellaria but for green and blue-green photobionts in a single joined thallus (photosymbiodeme), with a single mycobiont, and also when adjacent as co-primary photobionts. The different response is therefore a property of the photobiont. The results are consistent with published photosynthesis/water content response curves. The minimum thallus water content for positive net photosynthesis appears to be much lower in green lichens (15% to 30%, related to dry weight) compared to blue-greens (85% to 100%). Since both types of lichen rehydrate to about 50% water content by water vapour uptake only green lichens will show positive net photosynthesis. It is proposed that the presence of sugar alcohols in green algae allow them to retain a liquid pool (concentrated solution) in their chloroplasts at low water potentials and even to reform it by water vapour uptake after being dried. The previously shown difference in δ13C values between blue-green and green lichens is also retained in a photosymbiodeme and must be photobiont determined. The wide range of δ13C values in lichens can be explained by a C3 carboxylation system and the various effects of different limiting processes for photosynthetic CO2 fixation. If carboxylation is rate limiting, there will be a strong discrimination of13CO2, at high internal CO2 partial pressure. The resulting very low δ13C values (-31 to-35‰) have been found only in green lichens which are able to photosynthesize at low thallus water content by equilibraiton with water vapour. When the liquid phase diffusion of CO2 becomes more and more rate limiting and the internal CO2 pressure decreases, the13C content of the photosynthates increases and less negative δ13C values results, as are found for blue-green lichens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00776410
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  • 2
    Electronic Resource
    Electronic Resource
    Water vapor uptake and photosynthesis of lichens: performance differences in species with green and blue-green algae as phycobionts (1986)
    Springer
    Oecologia 71 (1986), S. 104-110 
    Details
    ISSN: 1432-1939
    Keywords: Lichens ; Humidity ; Water vapor uptake ; Photosynthesis ; Respiration ; Water relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dry 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377327
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  • 3
    Electronic Resource
    Electronic Resource
    Ecophysiological studies on orchids of Madagascar: incidence and plasticity of crassulacean acid metabolism in species of the genus Angraecum Bory (1998)
    Springer
    Plant ecology 135 (1998), S. 43-57 
    Details
    ISSN: 1573-5052
    Keywords: Angraecum ; Carbon isotope composition ; Crassulacean acid metabolism (CAM) ; Ecopysiology ; Madagascar ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The present study is an investigation on photosynthetic options in an orchid taxon and deals with the mainly epiphytes comprising genus Angraecum Bory. The incidence of crassulacean acid metabolism (CAM) in Angraecum species collected at various habitats in Madagascar was surveyed by analysis of stable carbon isotope composition (δ13C values). The values showed both inter- and intraspecific variability and suggest that in situ about 50% of the analysed species perform C3 photosynthesis, 20% moderate CAM (fixation of external CO2 during day-and night-time) and 30% pronounced CAM (CO2 uptake entirely during the night). The photosynthetic behaviour of the species indicated by the δ13C values was clearly related to the habitat from where the samples derived. In A. eburneum, A. sororium and particularly in A. sesquipedale the stable carbon isotope analysis was complemented by measurements of CAM performance under controlled conditions. The experiments with A. sesquipedale revealed that drought and temperature are important factors modulating CAM, whereas variation of the leaf-to-air water vapor pressure difference was less effective. Altogether, the results of the study support the view that the high biological adaptability and thus the ecological success of the genus Angraecum is largely based on genotypic diversity and intraspecific plasticity of the photosynthetic behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009787811077
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