The effect of mercury on the establishment of Pinus rigida seedlings and the development of their ectomycorrhizal communities

Metals are toxic to both plants and fungi, and elevated soil metal concentrations have been documented to change the structure of ectomycorrhizal communities. Mercury (Hg) is a highly toxic metal and inhibits the growth of ectomycorrhizal fungi (ECMF) in axenic culture. However, the effects of Hg on the growth of tree seedlings and the development of their ECMF communities have not been explored. In the current study, Pinus rigida seedlings were planted in soil amended with 0–366 μg g^?1 Hg and incubated for 5 months. Survival and growth of P. rigida seedlings was determined, and their ECMF communities were characterized by morphotype analysis. Seedling survival declined with increasing Hg additions, although no reduction in growth was detected among surviving seedlings. The addition of 88 μg g^?1 Hg to soil more than halved the total ectomycorrhizal colonization of root tips and reduced both richness and diversity of root tip morphotypes, while lower Hg additions did not significantly affect ECMF community composition relative to the no Hg control. This suggests that changes in the community of ECMF may occur in contaminated soils before any aboveground effects on surviving seedlings are noticeable, potentially altering the contribution of ECMF to the fitness of established host plants.