Fast acclimation of freezing resistance suggests no influence of winter minimum temperature on the range limit of European beech

Abstract

Low temperature extremes drive species distribution at a global scale. Here, we assessed the acclimation potential of freezing resistance in European beech (Fagus sylvatica L.) during winter. We specifically asked (i) how do beech populations growing in contrasting climates differ in their maximum freezing resistance, (ii) do differences result from genetic differentiation or phenotypic plasticity to preceding temperatures and (iii) is beech at risk of freezing damage in winter across its distribution range. We investigated the genetic and environmental components of freezing resistance in buds of adult beech trees from three different populations along a natural large temperature gradient in north-western Switzerland, including the site holding the cold temperature record in Switzerland. Freezing resistance of leaf primordia in buds varied significantly among populations, with LT50 values (lethal temperature for 50% of samples) ranging from-25 to-40 °C, correlating with midwinter temperatures of the site of origin. Cambial meristems and the pith of shoots showed high freezing resistance in all three populations, with only a trend to lower freezing resistance at the warmer site. After hardening samples at-6 °C for 5 days, freezing resistance of leaf primordia increased in all provenances by up to 4.5 K. After additional hardening at-15 °C for 3 days, all leaf primordia were freezing resistant to-40 °C. We demonstrate that freezing resistance of F. sylvatica has a high ability to acclimate to temperature changes in winter, whereas the genetic differentiation of freezing resistance among populations seems negligible over this small geographic scale but large climatic gradient. In contrast to the assumption made in most of the species distribution models, we suggest that absolute minimum temperature in winter is unlikely to shape the cold range limit of beech. We conclude that the rapid acclimation of freezing resistance to winter temperatures allows beech to track changing climatic conditions, especially during unusually warm winters interrupted by very cold weather.