Ectomycorrhizal fungi and the nitrogen economy of conifers-implications for genecology and climate change mitigation

The nitrogen (N) economy of conifers is hypothesized to reflect three spatially defined and interacting sources of variability in forest nutrition. These include the physiological adaptations of the host tree (N uptake capacities among populations), matched to the particular amount and nature of soil N supply (organic N, NH4+, and NO3-), as mediated by communities of site-adapted ectomycorrhizal (EM) fungi. The spatial attributes of an N economy may vary considerably over the ranges of tree species because of wide gradients in climate and soil fertility, underpinning a potentially important aspect of conifer genecology with implications for climate change mitigation. The evidence for an intersection of N supply with host demand, as mediated by EM fungi, will be briefly reviewed and then evaluated in light of assisted migration studies involving provenance trials of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in southwestern British Columbia. The trials were established across a wide range of site types, and so they provide valuable data on host response to gradations in soil N supply and interactions with local EM fungal communities. Preliminary results and knowledge gaps will be discussed under the framework of an N economy and management of forest genetic resources.