Chapter 1: The Characeae Plant

24
degrees of acclimation to low or high light intensities (Wang et al. 2008). In general, high
light intensities (that can be experienced in very shallow water, or very clear water) lead to a
contracted thallus with short internodes (Wang et al. 2008), whereas low light intensities (in
deep water or shaded situations) produce a more diffuse plant (Wang et al. 2008). Characeae
also respond to light intensity by modifying their pigment ratios (Wang et al. 2008) and in the
timing of reproduction (Wang et al. 2008). Exposure to light, and certain wavelengths of light
can also be important for stimulating germination of oospores (Sokol and Stross 1992),
although there is experimental evidence that although germination can take place in darkness,
light is required for establishment of the young thallus (de Winton et al. 2004).
1.5.4.2 Water chemistry and physical properties
The physical properties pH and conductivity (as an analogue for salinity or total dissolved
solids) are relatively easy to measure and have frequently been reported for charophyte
habitats, and it is common for tables of species to be listed in relation to these factors
(Corillion 1957, García and Chivas 2007). In general the most common species of
charophytes tolerate a range of pH values, with species of Chara preferring slightly alkaline
pH and species of Nitella preferring slightly acid to circum-neutral pH. There are a few
species that are found only in water with specific pH, but this is the exception rather than the
rule. To date there are no reports of a mechanism by which pH might select for, or influence
the distribution of characeae species. Salinity, on the other hand, imposes specific constraints
on the physiology and osmotic processes in charophyte cells. Several species of Chara and
Nitella can be found in, and appear to prefer slightly saline conditions. However, species in
the genera Lamprothamnium and Tolypella are frequently found in water of varying salinity,
and Lamprothamnium species can be the only plants occurring in waters with high salinity
(Brock and Lane 1980).
1.5.4.3 Nutrients
Characeae can take up nutrients through the above-ground thallus as well as through the
rhizoids (Littlefield and Forsberg 1965; Andrews 1987; Vermeer et al. 2003). Nitrogen is
preferentially accumulated as ammonium, and it can be circulated throughout the plant body
via cytoplasmic streaming (Vermeer et al 2003). In field studies characeae can have a major
impact on the nitrogen budget of lakes (Rodrigo and Alonso-Guillén 2008), responsible for
12 to 95 % of the total nitrogen content of the system. Characeae can also accumulate
phosphorus (Kufel and Ozimek 1991). Mean daily rates of phosphate uptake can exceed 27
nmol g -1 fresh weight h -1 (Andrews 1987).