Anatomy and physiology of sugar maple (Acer saccharum March) seedlings uninoculated or inoculated with the vesicular-arbuscular endomycorrhizal fungus Glomus etunicatum
Mycorrhizal inoculation improved the phosphorus (P) nutrition of sugar maple seedlings in the law P study soil. This improved P nutrition was not translated into growth, however. This was interpreted as evidence for the fungal carbohydrate drain or, perhaps, a threshold level of P needed for shoot growth was not reached in the low P soil even with the improved nutrition attributed to the fungus. In addition, inoculation reduced plant carbohydrate levels in the fall and affected the levels of various nutrients in plant parts. It was proposed that a more efficient endophyte, in terms of its effect on P nutrition versus carbohydrate use may have produced the classic growth response observed in other hardwood seedlings. Conversely, it is possible that sugar maple has a very limited dependency on the symbiosis. The results are applicable only to the particular host-endophyte-environment system present in the study. Microscopic analysis of infection development revealed cortical cell changes similar to those reported by other workers using either herbaceous or woody plant host. A slightly different pattern of arbuscule development was proposed. Intercellular hyphae were less common than intracellular hyphae. The beaded root morphology observed is limited to the genus Acer and did not appear to influence the infection process. The living arbuscule appears to be the site of transfer between the host and endophyte and the process is an active one.