Chapter 8 - PHOTOSYNTHESIS AND CARBOHYDRATE MOVEMENT

Abstract

Publisher Summary This chapter discusses photosynthesis by the intact lichen and its carbohydrate movement, interactions between lichen symbionts, and the rate and amount of carbohydrate movement. In many experiments on lichen material, net photosynthesis is measured as mg of CO 2 fixed per hour per gram dry weight. In lichens, where the autotrophic algae make up only a small fraction (by weight or by volume) of the complete thallus, net photosynthesis is significantly less than the true rate. The rate of photosynthesis is per milligram of chlorophyll because the amount of alga in lichens varies. Lichens can most easily tolerate very low temperature. The ability to withstand adverse conditions is necessary for lichens growing in an arctic environment. Very little is known about the factors that affect the rate or amount of carbohydrate movement between lichen symbionts. The carbohydrate transferred to the fungus by the lichen alga, at least in part, ends up as structural components of the growing thallus. In most lichens, the transferred carbohydrate is rapidly converted to mannitol. The rate of carbohydrate movement from the alga to the medulla region of the thallus varies in various lichens.