Consequences for ectomycorrhizal fungi of the selective loss or gain of pine across landscapes

Altered disturbance regimes and novel introductions are causing rapid shifts in the distribution of pines (Pinus L.). The functionally obligate symbiosis between pines and ectomycorrhizal (EM) fungi dictates that shifts in the distribution of one partner will affect the distribution of the other. In this review, we examine evidence for three hypotheses. (1) The loss of photosynthates through stress or tree mortality decreases the abundance of EM fungi and selects for less carbon-demanding species. (2) Pine introductions initiate establishment of novel EM fungal communities. (3) The extent of shifts in EM fungal abundance and community composition is mediated by surrounding vegetation. We find support for these hypotheses though changes in EM fungal abundance are variable and context-dependent. We posit that the consequences of shifts in EM fungal abundance and community composition extend beyond the individual tree to the landscape; these changes may affect population dynamics of both symbionts, ecosystem processes, and the conservation and evolution of fungi. In addition to conducting baseline surveys to assess the distribution of EM fungi, increasing our understanding of their function, morphology, propagation, and controls on host-specificity, and shifts would also assist in predicting the trajectory of ecosystems following the loss or gain of pine.