Assessment of the effect of mycorrhizal fungi on drought tolerance of conifer seedlings

Abstract

Methods were evaluated for comparing the potential of mycorrhizal fungi to increase the performance of conifer seedlings during water stress. The ability of five fungi to grow in pure culture under conditions of low water potential was tested. The same fungal isolates were then assessed in association with jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) seedlings. Mycorrhizal seedlings were subjected to known water stress by exposing their roots to a solution of polyethylene glycol or were planted into systems that allowed the simulation of a drought cycle in a forest soil. The apparent photosynthetic rate or the apparent photosynthetic rate and shoot and root growth were used as measures of seedling performance in the two systems. Fungi that grew well in pure culture under low water potential generally also increased the performance of black spruce. The ability of some fungi to form rhizomorphs extending into the mineral soil layer or to stimulate root growth also correlated with increased performance of black spruce. In contrast, under the experimental conditions used, jack pine showed good performance independent of mycorrhizal status. It is concluded that the screening methods used have value in selecting plant–fungus combinations that have potential to increase performance of conifer seedlings under drought stress. Key words: ectomycorrhizae, conifers, drought, Pinus, Picea.