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Thallus water content

After the absorption of water from the adjoining walls, the cytoplasm comes into balance with the swelling cell membrane (Renner, 1933). As soon as the semipermeability of the cytoplasm is restored, osmotic forces begin to act until the absorption and swelling forces are in equilibrium with the atmospheric humidity (Stocker, 1956). A very slow rate of water-vapor absorption is explained by its slower diffusion compared with liquid water. Water vapor is condensed mostly by the cell walls (Muller, 1909 Mayer and Plantefol, 1924 Stocker, 1927 Goebel, 1930). Attaining equilibrium with a vapor-saturated atmosphere is very slow. Because of the thick hyphal walls and swollen cortex, the difference between vapor pressure and thallus water content becomes small. Showman and Rudolf (1971) state that the... [Pg.387]

Wilske, B., Holzinger, R., Kesselmeie, J. (2001) Evidence for ethanolic fermentation in lichens during periods of high thallus water content. Symbiosis 31, 95. [Pg.309]

Connan S, Delisle F, Deslandes E, Ar Gall E (2006) Intra-thallus phlorotannin content and antioxidant activity in Phaeophyceae of temperate waters. Bot Mar 49 39-46... [Pg.167]

Regarding distances of soredia distribution, Bailey (1966a) illustrated that soredia of Lecanora conizaeoides are carried 61.0 cm by 2.2-mm-diameter rain drops falling 366 cm. He noted an increased wind speed was necessary for maximum soredia dispersal as the water content of the thallus increased. [Pg.118]

Starch and pyrenoglobuli are considered to be storage products of the phy-cobionts. While starch is produced only in hydrated and illuminated lichens, the globules are found also in dried thalli. Recently, Jacobs and Ahmadjian (1971a) hypothesized that the lipids of the plastoglobuli may function as a water source. The authors supported their idea by the fact that respiration persists in dry lichens at water contents of about 1% of the thallus dry weight (Ahmadjian, 1967). [Pg.155]

The second term on the right-hand side of the equation can be large, particularly under laboratory conditions where the water content of a thallus is high and the temperature between 18°-25°C. Thus, measurements of net photosynthesis can greatly underestimate the amount of carbon assimilation by lichen algae. [Pg.251]

The effect of the water content of a thallus on net photosynthesis has been noted earlier. Ried (1960b) showed that for Umbilicaria cylindrica the optimum rate was at 65% saturation but this was reduced by half when the thalli were fully saturated. He found, however, that in more loosely organized thalli, i.e., those without lower cortices (Peltigera) or with cyphellae(5ncra), photosynthesis was most rapid at 90% saturation with only a small decline above this level. He felt the decline was due to the difficulty of gas exchange in fully saturated leathery thalli such as Umbilicaria. However, the findings of Kershaw and Rouse (1971) with Cladonia alpestris, which has a hollow tubular thallus, casts doubt on this. [Pg.253]

Thallus moisture content is very critical, especially as the uptake and loss of water by lichen thalli is largely a physical process. The moisture content and rates of absorption and loss have been quite extensively studied (see Chapter 11). Henriksson and Simu (1971) reported the ability of Collema tunaeforme and Peltigera rufescens to recover their nitrogenase activity after long periods of desiccation. Storage was for periods of up to 30 weeks in plastic containers in the dark, at 12°C. After storage for periods longer than... [Pg.302]

Once the initial rapid uptake of water by lichens is over, the thalli often can absorb considerably more water during a prolonged immersion of several hours. The free spaces take up water rapidly but then the water content in the thallus increases due to the increased ability of colloids to retain water. We call such a phenomenon a state of oversaturation. Our experiments showed that this state was most pronounced with Ramalinafarinacea and R. fraxinea. During a 15-hour immersion, their thalli absorbed, respectively, 60 and 82% water in addition to the amount initially absorbed during the 30-second immersions. Umbilicaria grisea and UMrsuta took up additionally only 8.2 and 7.7% water, respectively. Other investigated species were of intermediate values. [Pg.383]

Being similar in its character to the absorption of liquid water and also displaying a typical picture of swelling, the absorption of water vapor is several thousand times slower. In a humid atmosphere the water content of a thallus will slowly increase until it reaches a constant equilibrium value. The higher the relative atmospheric humidity, the higher is the equilibrium water content in the thallus and the longer it takes to reach equilibrium. [Pg.384]

The results of our experiments have shown that the relationship of water content in the thallus when the lichen is in a saturated atmosphere (in equilibrium with vapor pressure) to the water content in a thallus saturated by liquid water differs greatly in lichens. The lowest values were shown by Collema flaccidum (14%), C. cristatum (20%), Aspicilia esculenta (22%), and A. fmticulosa (23%). The highest values were held by Cetraria islandica (64%) and Dermatocarpon miniatum (68%). For most fruticose and foliose lichens the relation between the water content in the thallus in equilibrium with vapor pressure of the saturated atmosphere and the maximum saturation with liquid water was within 40-50%. [Pg.385]

The study of the lichen s ability to use water vapor from a nonsaturated atmosphere is of particular interest. The main part of the water in a vapor state absorbed by lichens enters the thallus only at a relative humidity that is above 90%. For foliose and fruticose lichens placed in an atmosphere with a relative humidity of 95%, Butin (1954) and Ried (1960b) found that the maximum amounts of water absorbed by the thalli were 30-50% of the water content of thalli fully saturated with liquid water. These findings were confirmed by our experiments (Fig. l)(Blum, 1965). The absorption of water vapor as well as liquid water to a certain extent depends on anatomical and morphological peculiarities of lichens. That is why various species have marked differences in the rate and amount of water vapor absorbed from equal relative atmospheric humidities. These differences become more pronounced with the increase of water vapor content in the atmosphere. [Pg.385]

Very little is known about the osmotic pressure of the cells of lichens. Using Neubauer s (1938) measurements of the water content of lichen thalli in atmospheres with low relative vapor pressure humidity over a saturated solution of NaCl, Barkman (1958) calculated that the osmotic pressures of lichens were 300-1300 atmospheres. However, according to Smith (1962), much of the water in the thallus is held external to the cytoplasm in the cell walls, and thus these remarkably high values for osmotic pressure are not applicable only to the living cell contents. Barkman s estimates should be regarded as analogous to the estimates of the osmotic pressure of gels. [Pg.388]

Water content in an oversaturated state (% of dry weight) after immersion of the saturated thallus for... [Pg.391]

Most lichens, except gelatinous forms, accumulate less water during saturation than other cryptogamic plants (fungi, algae, and mosses). Water accumulation in the thallus is very uneven. Different parts of the thallus and its layers contain different amounts of water. There are no data about the water content of mycobiont and phycobiont cytoplasm, but it is considered to be small. [Pg.392]

Mist also influences the water content of a thallus. Stocker (1927) considered misty days to be especially favorable for lichens because small drops of water carried by the wind assure the thalli of an even and prolonged moistening. Also, even on dense, foggy days the amount of diffused light (according to Stocker) is sufficient for assimilation. The ecological importance of mist is great because of its ability to retain water loss in the thallus (Butin, 1954). [Pg.394]

Harris and Kershaw (1971) found that the Trebouxia phycobionts of Parmelia physodes and Parmelia sulcata stored starch only when the thalli were kept for several days in the light at low water contents or after the thallus dried slowly in the light. When the thalli were saturated with water. [Pg.576]

Along with many other authors, LeRoy and Koksoy have drawn-attention to a common source of error in the studies of the mineral content of lichens. It is difficult to avoid the contamination of the samples by the substratum, because of the close contact of the species with it and even the decaying of the lower parts of the thallus. Other sources of error that they mentioned are the composition of surface and near-surface water, age of the thalli, the contamination from the atmosphere, and soil that was not removed from the thalli during cleaning for the experiments. Radioactive fallout, also mentioned as a possibility, is of secondary importance with respect to inactive nuclides, because the absolute mass of a certain radionuclide representing a rather high radiation effect is usually vanishingly small compared with the inactive mass of that element. [Pg.192]

The content of water in thalli that are in equilibrium with vapor pressure in a saturated atmosphere is lower than that attained after the absorption of liquid water because in a saturated atmosphere the lichen does not contain capillary-drawn liquid water in its thallus and water on its surface. According to the data obtained by a number of authors (Smyth, 1934 Ellee, 1939 Quispel, 1943 Butin, 1954) saturation by water vapor reaches a level of 50-75% of the maximum amount of water in a thallus saturated with liquid water. However, Ried (1960b) doubts the reality of this data and considers the findings to be overstated because of the possibility of... [Pg.384]


See other pages where Thallus water content is mentioned: [Pg.254]    [Pg.254]    [Pg.82]    [Pg.218]    [Pg.230]    [Pg.327]    [Pg.382]    [Pg.386]    [Pg.390]    [Pg.392]    [Pg.393]    [Pg.394]    [Pg.394]    [Pg.395]    [Pg.395]    [Pg.79]    [Pg.287]    [Pg.228]   
See also in sourсe #XX -- [ Pg.390 , Pg.391 , Pg.392 , Pg.393 , Pg.394 ]




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