Within-thallus variations

Fairhead et al. (2005b) examined small-scale within-thallus variations in the phlorotannin contents of D. anceps and D. menziesii and also compared individuals collected from different sites at Anvers Island as well as from the upper and lower limits of their depth distributions at those sites. Thirteen defined thallus parts within each individual were sampled, and although there was considerable variation within individuals at that spatial scale, there were no consistent patterns. When fine scale parts within the individuals were grouped, the main axis of D. anceps had significantly lower phlorotannin levels than did lateral branches. In D. menziesii, the distal-most tips of the lateral branches had significantly higher phlorotannin levels... 

Fagerstrom T, Larsson S, Tenow O (1987) On optimal defence in plants. Func Ecol 1 73-81 Fairhead VA, Amsler CD, McClintock JB, Baker BJ (2005a) Within-thallus variation in chemical and physical defences in two species of ecologically dominant macroalgae from the Antarctic Peninsula. J Exp Mar Biol Ecol 322 1-12... 

Hitch (1971) studied the environmental factors affecting nitrogenase activity in lichens, and has reported diurnal and seasonal variation in Collema, Lichina, and Peltigera. When samples collected from the field in a desiccated state were wetted, nitrogenase activity started after lag periods of 60, 20, and 35 minutes, respectively. The thallus moisture contents, however, changed from the original level of 20% oven-dry weight to 200% within... 

These two control mechanisms undoubtedly act in unison to effect a coarse and a fine adjustment of the amount of light reaching the phycobiont layer. The lichen-acid screen contributes a seasonal control while variation in moisture content of the cortex exerts a variable diurnal control within the limits of light transmission set by the lichen-acid screen. The dorsal limit of the phycobiont layer can be considered to coincide with that part of the thallus above which the majority of the phycobiont cells cannot survive because of excessive light. Similarly,the ventral boundary indicates the limit of light intensity below which the majority of cells cannot survive. 

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