PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS

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Abstract
SUMMARY: The seasonal levels of nitrogenase activity in Peltigera praetextata and P. canina var. rufescens have been examined at 5, 10, 15, 20, 25, 30, 35°C, under 75, 150, 300 and 450 μEinsteins m−2 s−1 illumination and for all levels of thallus moisture content. The results show only a small increase in activity at high light intensities but a marked temperature optimum at 25–30 C in both species. Of outstanding interest however are the very large rate changes occurring throughout the year. The changes are clearly evident at all temperatures and light levels.These results are discussed in relation to concurrent seasonal changes of net photosynthetic rate and the need for experimental design of physiological work in a multivariate framework is strongly emphasized.