Mountain birch under multiple stressors--heavy metal-resistant populations co-resistant to biotic stress but maladapted to abiotic stress.

Stress adaptations often include a trade-off of weakened performance in nonlocal conditions, resulting in divergent selection, and potentially, genetic differentiation and evolutionary adaptation. Results of a two-phase (greenhouse and field) common garden experiment demonstrated adaptation of mountain birch (Betula pubescens subsp. czerepanovii) populations from industrially polluted areas of the Kola Peninsula, north-western Russia, to heavy metals (HM), whereas no adaptations to wind or drought stress were detected in populations from wind-exposed sites. HM-adapted seedlings were maladapted to drought but less palatable (co-resistant) to insect herbivores, even under background HM concentrations. The absence of adaptations to harsh microclimate and the generally high adaptive potential of mountain birch, a critical forest forming tree in subarctic Europe, need to be accounted for in models predicting consequences of human-driven environmental changes, including the projected climate change.