The effects of sewage effluent on endomycorrhizal development in Acer

Secondarily treated sewage effluent was sprayed into a 50-year-old beech–maple forest near Harbor Springs, Emmet County, Michigan. Effluent was applied at rates of 0, 3.8, and 7.6 cm per week onto thinned and unthinned plots during the growing seasons of 1978 and 1979. Each spray rate and density combination was replicated four times. Acer sp. roots were examined each growing season to evaluate development of endomycorrhizae. Numbers of mycorrhizae were significantly greater in the sprayed than in the unsprayed plots but did not vary significantly with month or thinning.