Mycorrhizae of landscape trees produced in raised beds and containers

Mycorrhizal associations provide a linkage between tree roots and the soil, thereby contributing to the tolerance of trees to environmental stresses. Little, however, is known about the mycorrhizal status or dependency of many landscape trees. The objective of this study was to quantify mycorrhizal root colonization and spore formation on a diverse collection of ornamental tree species grown in raised beds or containers at an established tree farm in central Florida. In addition, root diameters were measured to determine if there was a relationship between this parameter and mycorrhizal formation. A total of 23 tree species were sampled; 9 were present both in containers and raised beds, 6 species were present in containers only, and 8 species were present as embedded plants only. The proportion of root length colonized by mycorrhizal fungi ranged from 0% to 83%. Mean arbuscular mycorrhizal spore numbers ranged from <20 to nearly 500 spores 100 g^-1 (3.5 oz^-1). Mean root diameters ranged from < 500 to > 1,000 μm (0.0197 to 0.0394 in.). No relationship was found between root coarseness and mycorrhizal root colonization or sporulation. The majority of trees formed mycorrhizae of the arbuscular type. Five species in the family Pinaceae or Fagaceae had the potential to form ectomycorrhizae; however, they were poorly colonized. Future research should be directed toward understanding the importance of mycorrhizae to landscape trees, including effects on tree survival and growth and the effect of fertilizer and pesticide applications on mycorrhizal development.