Differential Growth Response to the Mycorrhizal Fungus Glomus fasciculatus of Southern Magnolia and Bar Harbor Juniper Grown in Containers in Composted Hardwood Bark-shale1

Abstract

Abstract Plants of southern magnolia ( Magnolia grandiflora L.) and ‘Bar Harbor’ juniper ( Juniperus horizontalis Moench) were grown in a composted hardwood bark: expanded shale medium in 7.6 cm square containers in a greenhouse. All plants received either a low rate (1.1 kg/m 3 ) or the manufacturer's recommended rate (4.5 kg/m 3 ) of 18N-6P-12K slow-release fertilizer, and half the plants received inoculum of Glomus fasciculatus . After 6 months, height of magnolia plants inoculated with G. fasciculatus was nearly twice that of uninoculated plants, and the height difference between the two groups of plants increased with time. In contrast, plants of ‘Bar Harbor’ juniper demonstrated little or no growth response to infection with the mycorrhizal fungus. Fertilization of magnolia plants at the recommended rate as compared with ¼ that rate did not inhibit the degree of mycorrhizal infection of roots. Roots of inoculated ‘Bar Harbor’ juniper plants were heavily infected at both fertilizer rates, but the degree of infection was significantly greater at the lower fertilizer rate.