In Situ Measurement of the Water Content of Lichens
The distribution of plants and the development of individuals at a certain location depend to a considerable degree upon microclimate. This is true for phanerogams as well as for lichens. For lichens, however, crucial environmental influences occur on a m
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PROTOCOL
In Situ Measurement of the Water Content of lichens GUNTER SCHUSTER, SIEGLINDE OTT, ANDRE GASSMANN,
and JUDITH ROMEIKE
Introduction The distribution of plants and the development of individuals at a certain location depend to a considerable degree upon microclimate. This is true for phanerogams as well as for lichens. For lichens, however, crucial environmental influences occur on a much smaller scale (Scholler 1991, Canters et a1. 1991). The microclimate of a higher plant is defined by the environmental conditions that occur within an area of about 1 m 2 around the plant. However, for lichens important changes occur within a few cm2• Lichenologists frequently refer to the microclimate of phanerogams as mesoclimate. This difference in scale of the microclimate is the only difference, as the contributing features are identical for both groups of organisms. Air and substrate temperature, solar irradiance, air humidity, water supply and wind speed are the most important parameters. Because the microclimatic observation areas are small for lichens, the sensors also have to be small. Measurement of water availability is a special problem, as it is subject to a very quick change in poikilohydrous thalli (Larson 1979). This chapter describes a new method for measuring water content using thallus impedance. This allows microhabitats to be compared with each other, especially if these measurements are combined with those taken from sensors for solar irradiance, thallus temperature and air temperature. In the field, the method is superior to gravimetric methods that have inaccuracies caused by repeatedly removing the thalli. Thallus water content is determined by wind, irradiation, and temperature, and is
~ Gi.inter Schuster, Universitat Di.isseldorf, Botanisches Institut, Universitatsstr. 1, Di.isseldorf, 40225, Germany (phone +49-211-81-13479; fax +49-211-81-l2881; e-mail [email protected]) Sieglinde Ott Andre Gassmann Judith Romeike
I. C. Kranner et al. (eds .), Protocols in Lichenology © Springer-Verlag Berlin Heidelberg 2002
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also influenced by substrate type (Ott et al. 1997). For this reason, all these parameters should be measured at the same time. When determining the water content of lichens, always note that water loss from poikilohydric thalli occurs very fast, even if a compact cortex or gelatinous water storage tissues retard the process. Water absorption is a slower process, and depends on the water source, the anatomy of the thallus and its impregnation with more or less hydrophobic substances. Finely distributed droplets, in the form of fog and mist, are optimal for absorption while large raindrops run off (Jahns and Ott 1983). Most lichens can take up water from the air. This process is asymptotic, and saturation is reached much later than expected, often only after days (Jahns 1984). In the thallus, water is mainly stored in the hyphal walls and in gelatinous substances. The capillary regions between the hyphae, necessary
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