Ectomycorrhizal colonization and intraspecific variation in growth responses of lodgepole pine

Across different host plant species, the effects of mycorrhizal colonization on host growth parameters can vary, but intraspecific variation in this relationship has rarely been measured. We tested the direction and consistency of the relationship between ectomycorrhizal colonization level and growth responses across seed families of Pinus contorta var. latifolia. Root tips of seedlings from eight full sib seed families varied in levels of ectomycorrhizal fungal colonization from 39% to 100%. We observed positive, negative, or neutral relationships between colonization level and shoot mass, depending on plant family. For the majority of seed families no relationship was observed between colonization level and root mass; however, two seed families showed negative relationships. Shoot height differed only by seed family. Results from our study indicate that the relationship between colonization level and host growth depends on host genotype. We suggest that models of plant intraspecific interactions should consider ectomycorrhizal associations when assessing phenotypic variability.