Mycorrhiza and tree nutrition in poor forest soils

When fertilizing forest trees with nitrogen a great quantity is bound in organic humus compounds and cannot be utilized by the trees. Extensive reserves of bound nitrogen also exist in comparatively poor forest soils. However, it has been found that it is possible to release these reserves by inoculation with certain soil fungi of the litter-decomposing type. It does not seem improbable that such measures can represent a biological alternative to chemical fertilization. In the present paper it is shown how Boletus subtomentosus, that normally is a mycorrhiza forming fungus, can stimulate the development of pine plants. A physiological strain of this fungus is used which has the ability to decompose litter. The typical mycorrhiza fungus Boletus bovinus also stimulated the plant growth to a certain extent. However, the stimulating effect ceased when strong fertilization was used or when the light intensity was reduced. Constant illumination resulted in the plants developing well and with good mycorrhiza formation. When the period of illumination was reduced to 16 hours a day the plants developed less vigorously and the mycorrhiza formalion was reduced.