Ecto- and Endomycorrhizae of Arctic Plants at Barrow, Alaska

Abstract

The increased growth and dependence of many green plants on the presence of mycorrhizae has long been known and appreciated by biologists (Marks and Kozlowski, 1973). The early research dealt with ectomycorrhizal fungi and a series of experiments clearly indicated that greater uptake of nitrogen and phosphorus from infertile soils occurred when mycorrhizae were present. Nutritional studies of selected mycorrhizal fungi by Palmer and Hacskaylo (1970) indicated that most of these fungi utilized simple sugars most efficiently. In fact, they were unable to degrade lignin, cellulose, pectin, and other complex carbohydrates. This nutritional mode contrasted sharply with the typical fungal decomposers which possess this ability along with a faster growth rate and the ability to grow on a wide variety of natural and artificial substrates. In 1965, Lewis and Harley first described the one-way movement of carbohydrates from host roots to the mycorrhizal fungus. In this process sugar is converted by the fungus to trehelose and mannitol and eventually to the storage polysaccharide, glycogen. The host plant cannot utilize these sugars. Bevege, et al. (1975) confirmed this phenomenon with Pinus radiata and Rhizopogon luteolus. They reported the same process in the endomycorrhizal hyphae of Endogone but only a minute amount of sugar was incorporated by the fungus. The difference seems to lie in the ability of the ectomycorrhizal fungus to act as a nutrient sink. Nevertheless, both fungal-root associations have the overall effect of increasing plant growth dramatically.