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  • 1
    Digitale Medien
    Digitale Medien
    Carbon dioxide exchange in lichens: Partition of total CO2 resistances at different thallus water contents into transport and carboxylation components (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 52 (1981), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The total resistances to CO2 uptake by Sticta latifrons Rich, and Pseudocyphellaria amphisticta Kremp. were separated into transport and carboxylation components by calculation after transformation of net photosynthesis rate against CO2 concentration curves into a linear form. The use of this technique circumvented the problem of measuring the internal CO2 concentration of the lichen thalli. Both species exhibited an increase in transport resistance at high thallus water contents and an increase in both transport and carboxylation resistances at low water contents. At low and intermediate water contents internal transport resistances were larger than carboxylation resistances when measured at limiting CO2 concentrations. However, at ambient CO2 concentrations carboxylation processes were the dominant factors limiting photosynthesis at all, except the high, water contents.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1981.tb02709.x
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  • 2
    Digitale Medien
    Digitale Medien
    Carbon dioxide exchange in lichens: Estimation of internal thallus CO2 transport resistances (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 52 (1981), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The gaseous exchange pathways of Sticla latifrons Rich. and Pseudocyphellaria amphisticta Kremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO2 diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO2 and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1981.tb02710.x
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  • 3
    Digitale Medien
    Digitale Medien
    A comparison of photosynthesis in two thalloid liverworts (1982)
    Springer
    Oecologia 54 (1982), S. 275-280 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Standard infra-red gas analysis techniques were used to compare the photosynthesis of the liverworts Marchantia foliacea Mitt. and Monoclea forsteri Hook. Parameters measured include net photosynthetic rates, light response curves, quantum efficiencies, diffusive resistances to CO2 and water, apparent photorespiration and chlorophyll content. A series of morphological measurements were also made to determine resistance of pores and the ‘mesophyll’ to dorsal surface ratio, A mes/A. Marchantia has a cuticularised thallus with the photosynthetic tissues arranged in air chambers giving an A mes/A of 9 whilst Monoclea has a solid thallus, A mes/A of 1. Both species are shade adapted and it was found that whilst the air chambers were advantageous for water relations they increased maximum photosynthesis only slightly. Calculations showed that the solid thallus would be photosynthetically superior in very moist environments. The results are discussed with reference to existing ideas on the evolution of the structure of land plants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00378404
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  • 4
    Digitale Medien
    Digitale Medien
    Utilisation of pressure-volume techniques and non-linear least squares analysis to investigate site induced stresses in evergreen trees (1983)
    Springer
    Oecologia 57 (1983), S. 380-390 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Detailed statistical analysis of data obtained from five species of New Zealand native trees was used to develop an empirical model of pressure-volume curves. The model combines an exponential turgor function with a hyperbolic osmotic function and provides a very good fit to all data sets. The resultant function permits precise calculation of the bulk modulus of elasticity and turgor loss point from simple manipulation of the coefficients as well as providing the usual estimates of osmotic potential and free water content. The use of several water relations parameters, rather than one or two, each expressing different ecological aspects has permitted a better insight into the adaptability of the species. The data was obtained as part of an investigation into the causes of forest mortality to examine the tissue water relations of the principal species and to assess their ecological status. For all parameters highly significant differences were found between species. Silver beech (Nothofagus menziesii) and quintinia (Quintinia acutifolia) or tawari (Ixerba brexioides) are well separated and are consistently placed in opposing groups by the parameters. Osmotic potential proved to be of limited value for differentiating sites possibly because of the greater amplitude of diurnal variation compared with the site differences and also because of large within site variation. However variations in the pressure potential at the turgor loss point, which was closely correlated with osmotic potential, discriminated the levels of effective precipitation at the study sites, and the drought tolerance of the species. For one species, tawari, it proved possible to classify the sites on the basis of water content at the turgor loss point and osmotic potential using discriminant analysis. Variation in the water potential at the turgor loss point, which was closely correlated with osmotic potential, can be used to rank the species in order of drought adaptability and this was found to coincide with their order of permanence on the site. The bulk modulus of elasticity and the coefficient of elasticity are closely linked but their value in the ecological comparisons was limited by higher variability than found for other parameters. Ranking of the species using the variability of the parameters indicates the presence of to two distinct survival strategies; stress avoidance and stress tolerance. The two canopy species utilise opposing strategies and may be less at risk than the seral plants which combine both strategies. The data provides evidence for current stress on the unhealthy site which most stongly affects the seral species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00377184
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  • 5
    Digitale Medien
    Digitale Medien
    A comparison of photosynthesis in two thalloid liverworths (1983)
    Springer
    Oecologia 57 (1983), S. 420-420 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00377190
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  • 6
    Digitale Medien
    Digitale Medien
    Terrestrial vegetation at Canada Glacier, Southern Victoria Land, Antarctica (1992)
    Springer
    Polar biology 12 (1992), S. 397-404 
    Details
    ISSN: 1432-2056
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Bryophyte flushes in the vicinity of Canada Glacier in S.S.S.I. No. 12, Taylor Valley, Southern Victoria Land, were investigated in order to describe the vegetation present and to investigate factors affecting vegetation distribution. Biomass values from 950 to 1,250 g m−2 (dry weight) and vegetated areas up to 14,450 m2 indicate this is a significant area of bryophyte growth in Southern Victoria Land. The pattern of plant species in relation to water flow was investigated through detailed mapping. This is the first confirmed identification of Bryum argenteum, and Pottia heimii, and the first report of Bryum pseudotriquetrum from this area. Tissue nitrogen values for plants at this site are lower than other reported data, but it seems unlikely this would be a limiting factor for growth. It is concluded that, in this area, summer water flow in conjunction with microtopography has the greatest influence in determining where mosses, cyanobacteria and algae grow.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00243110
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  • 7
    Digitale Medien
    Digitale Medien
    Invertebrates associated with moss communities at Canada Glacier, southern Victoria Land, Antarctica (1993)
    Springer
    Polar biology 13 (1993), S. 157-162 
    Details
    ISSN: 1432-2056
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The invertebrate faunal composition of moss-dominated flushes near the Canada Glacier was, as in similar habitats in continental Antarctic regions, numerically dominated by protozoa, rotifers, nematodes and tardigrades. Mites were of lesser abundance. Although collembola occur in the Taylor Valley, none were found at the study site. The finding of a catenulid flatworm is significant as microturbellarians have only rarely been recorded from Antarctica. Nematode, tardigrade and rotifer densities recorded were comparable to those in other Antarctic regions. These groups were found at a mean depth ranging from 5 to 10.83 mm in the moss. A greater percentage of all groups were in the upper 5 mm of moss cores in post-melt samples than in pre-melt samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00238925
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  • 8
    Digitale Medien
    Digitale Medien
    Small-scale field mapping of lichen distribution in three dimensions with a computer-based position-tracking system (1999)
    Springer
    Oecologia 119 (1999), S. 552-556 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words Electromagnetic Tracker ; Three-dimensional mapping ; Species composition ; Species distribution ; Topography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A trial was undertaken with an electromagnetic position-tracking (Tracker) system by mapping a small section of a lichen habitat near Cape Royds, Ross Island, Antarctica. This method facilitated the simultaneous collection of precise information about both the topography of the site and the distribution of lichen species. These data were used to produce accurate maps and three-dimensional reconstructions of the mapped area. The technique offers considerable savings in time over conventional methods used in plant and lichen surveys, and has potential to enhance the information collected from broader-scale transect surveys.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050818
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  • 9
    Digitale Medien
    Digitale Medien
    Chlorophyll a fluorescence and CO2 exchange of Umbilicaria aprina under extreme light stress in the cold (1998)
    Springer
    Oecologia 113 (1998), S. 325-331 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key wordsUmbilicaria aprina ; CO2 exchange ; Chlorophyll a fluorescence ; Low temperatures ; Photoinhibition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A lichen growing in a continental Antarctic region with low temperatures and strong irradiance in summer was investigated for evidence of photoinhibition. Field experiments with Umbilicaria aprina from a sheltered site with heavy snowpack showed no effects of photoinhibition when the lichen was exposed to strong sun irradiance for nearly 11 h a day. This was evident from CO2 exchange and simultaneous chlorophyll a fluorescence measurements. CO2 exchange was also not affected if quartz glass allowing greater UV penetration, was used as a lid for the cuvette. The dependency of net photosynthesis on photosynthetic photon flux density suggests that the lichen is photophilous.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050383
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  • 10
    Digitale Medien
    Digitale Medien
    Do secondary substances in the thallus of a lichen promote CO2 diffusion and prevent depression of net photosynthesis at high water content? (1997)
    Springer
    Oecologia 112 (1997), S. 1-3 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words Lichen acid ; Lichen substances ; Photosynthesis ; Lichen ; Water content
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Many lichens show seriously depressed net photosynthesis (NP) at high thallus water contents due to increased carbon dioxide diffusion resistance through blockage of diffusion pathways by water. The soil lichen Diploschistes muscorum, however, shows no depression and NP is close to maximal even at the highest thallus water content. We investigated whether lichen substances (lecanoric and diploschistesic acids) in the cortex and medulla contributed to this ability to maintain high NP. Dry thalli were extracted with water-free acetone and, after this treatment, were found to be fully viable to the extent of continued growth after replanting in the field. No differences were found in the response of NP to thallus water content between the normal and extracted thalli, in fact the response curves were often nearly identical. Thus, in this species it seems that lichen substances did not maintain the water-free diffusion pathways and some other explanation, possibly structural, needs to be sought.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050275
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