Phenotypic differences in the seasonal pattern of net photosynthesis in Cladonia stellaris

Despite the contrasting thermal and light environment of sun and shade ecotypes of Cladonia stellaris, analysis of the pattern of net photosynthesis throughout the year as well as enzyme polymorphism in each morphotype has found little genotypic difference. The large disparity between photosynthetic capacity in the sun and shade replicates is shown to be due to a difference in chlorophyll content. There is a significant decline in photosynthetic capacity in November and this is shown to be reversible uncoupling of energy transduction in some photosynthetic units during the winter period. The control of coupling and uncoupling of photosynthetic units is found to be mediated by both day length and thallus temperature and a double environmental signal in June and July of short days coupled to low temperature will initiate and finalize the event within 12 h. This response pattern is discussed in relation to identical capacity changes in other lichen species. Apart from a single isoenzyme difference in esterase polymorphism, no differences in the zymograms of leucine aminopeptidase, phosphoglucoisomerase, or acid phosphatase were detected and this overall genetic homogeneity was equally evident in a general protein gel. This unexpected degree of homogeneity is discussed in terms of the difficulties in assessing enzyme polymorphisms in different plant populations, without maximum refinement of protein preparation methods and electrophoretic techniques. It is concluded that the two quite distinct sun and shade morphotypes only reflect phenotypic differences. In contrast, however, significant differences are reported in the distribution of specific enzymes between the tops and bases of the podetia.