Seedling genetics and life history outweigh mycorrhizal network potential to improve conifer regeneration under drought

The objective of this study was to determine whether interior Douglas-fir (Pseudotsuga menziesii var. glauca) seedling establishment is affected by the presence of an ectomycorrhizal network (MN), and whether this varies by regional climate, seed provenance and seedling life history. We examined how MN facilitation varied with seedling provenance by planting interior Douglas-fir seed and nursery-grown seedlings near the crown edge of mature conspecific trees along a climatic stress gradient. Survival of outplanted nursery seedlings was greatest for the medium moisture provenance, but decreased with drought more rapidly than the wet or dry provenances. The driest provenance performed best under severe drought, but the survival of all provenances was still less than 35% under severe drought. Survival, growth and δ13C of seedlings grown from seed or in the nursery were not affected by MNs. We conclude that seedling genetic and life history effects outweigh benefits that MNs may incur upon Douglas-fir seedling performance under conditions of severe drought. Selection of appropriate provenances and robust growing stock will become of increasing importance for regenerating sites where drought is expected to increase with climate change.

► Douglas-fir seedlings were grown near the crown edge of trees along a drought stress gradient.
► Seedlings were varied by provenance, and whether they were linked to networks of mature trees.
► Seedling survival, growth and water use efficiency were assessed after two growing seasons.
► Seedling performance was affected by climate, provenance, and life history, but not networks.
► Seedling genetics outweighed the facilitative effects of networks at the crown edge of mature trees.