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

Abstract

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.

Electrophoretic variation in a population of the lichen Peltigera rufescens (Weis.) Mudd

“…Studies correlating enzymatic variation with population or morphotype variability have also met with limited success. Kershaw et al (1983) and MacFarlane et al (1983) found minimal differences in acid phosphatase, PGI, MDII and leucine amino pepsidase stains in distinct sun and shade populations ot Cfadoitta rangtferiita and C. stellaris. I'ahselt & Hageman (1983) found little difference between isolated stands of (\^traria arenaria, while the highly \ariable morphology of Cladonia cristatella appears to be unrelated to electrophoretic differences (Fahselt, 1986).…”

“…Thus studies must rely on field obseryations and shortterm manipulations of thalli collected from the field. Often, the experiments are designed such that comparisons are made between diflerent populations of the lichen species (Kershaw et al, 1983 ;MacFarlane, Kershaw & Webber, 1983;Brown & Kershaw, 1984), These populations are defined on an ecological basis, usitig characteristics such as geographic location, morphology and microsite yariation. Sexual recombination in lichens is thought to be infrequent, the main reproductive outlet being yegetative propagation via fragmentation, isidia or soredia.…”

“…Until now, within-site variation has been considered minimal (Fabselt & Hageman, 1983) and has been downplayed in recent studies to such an extent that this variation is usually eliminated by combining individual samples within a site to form a single replicate (MacFarlane et al, 1983;Kershaw et al, 1983;Brown & Kersbaw, 1985). ^^bis practice will now bave to be reexamined, as a more extensive witbin-site comparison may be required to validate any between-site variation observed in experimental studies.…”

“…Fven witbin a small area (60 m~), microsite variation and founder effects can have a large influence on tbe enzymatic expression of the thallus, as shown by the significant correlation between tbe ordination of tbe banding patterns and the distance separating the rosettes vvitbm a site in the !\Iay collection (Figs 1, 2). Until now, within-site variation has been considered minimal (Fabselt & Hageman, 1983) and has been downplayed in recent studies to such an extent that this variation is usually eliminated by combining individual samples within a site to form a single replicate (MacFarlane et al, 1983;Kershaw et al, 1983;Brown & Kersbaw, 1985). ^^bis practice will now bave to be reexamined, as a more extensive witbin-site comparison may be required to validate any between-site variation observed in experimental studies.…”

Physiological‐environmental Interactions in Lichens

“…There are two distinct ecotypes, one characteristic of full solar radiation conditions and the other characteristic of dense shade under virtually closed canopy conditions. The parallel study which is reported elsewhere (Kershaw, MacFarlane and Webber, 1983) contrasts two equivalent ecotypes of C. stellaris from under closed spruce canopy and completely open lichen woodland in northern Ontario. In both situations, sun and shade ecotypes have been examined in terms of their seasonal patterns of gas exchange in parallel with an examination of the potential polymorphism of a number of selected enzymes.…”