Functional analysis of the intrathalline and intracellular chlorophyll concentrations in the lichen family umbilicariaceae

Abstract

Intrathalline and intracellular chlorophyll concentrations together with thallus structure were studied in 12 species of the lichen family Umbilicariaceae in order to explore pigment limitations for light absorption and for maximum rates of net photosynthesis (A(max)). Species from high light environments tended to have relatively low chlorophyll concentrations and vice versa. Chlorophyll concentration on a surface area basis of all species studied was sufficient to absorb 80-99% of the incident light, which led us to believe that chlorophyll concentration was not a limiting factor for A(max). A(max) of Umbilicariaceae was smaller than A(max) of leaves of vascular plants, both on a dry weight and on a surface area basis. These differences slightly decreased but did not disappear when referred to the chlorophyll concentration of the photosynthetic tissues, but reference units had a confounding effect in the comparisons. Differences in A(max) on a dry weight basis between Umbilicariaceae and vascular plants disappeared when comparisons were made with the whole plant and not simply with the leaf. We found a significant, inverse relationship between amount of alga and chlorophyll concentration within the algal cells in the lichens studied. This was interpreted as a mechanism to avoid pigment self-shading within the algal layer, distributing more efficiently the photosynthetic pigments over a given surface area, and is the first indication of such a mechanism in lichens. It is suggested that thallus structure and physiology have a larger influence on the observed low A(max) of the lichens studied than chlorophyll content.