Vernal freeze damage and genetic variation alter tree growth, chemistry, and insect interactions. (6th October 2017) - Rubert‐Nason, Kennedy F.
Abstract: Anticipated consequences of climate change in temperate regions include early spring warmup punctuated by intermittent hard freezes. Warm weather accelerates leaf flush in perennial woody species, potentially exposing vulnerable young tissues to damaging frosts. We employed a 2 × 6 randomized factorial design to examine how the interplay of vernal (springtime) freeze damage and genetic variation in a hardwood species ( Populus tremuloides ) influences tree growth, phytochemistry, and interactions with an insect herbivore ( Chaitophorus stevensis ) . Acute effects of freezing included defoliation and mortality. Surviving trees exhibited reduced growth and altered biomass distribution. Reflushed leaves on these trees had lower mass per area, lower lignin concentrations, and higher nitrogen concentrations, altered chemical defence profiles, and supported faster aphid population growth. Many effects varied among plant genotypes and were related with herbivore performance. This study suggests that a single damaging vernal freeze event can alter tree–insect interactions through effects on plant growth and chemistry. Differential responses of various genotypes to freeze damage suggest that more frequent vernal freeze events could also influence natural selection, favouring trees with greater freeze hardiness, and more resistance or tolerance to herbivores following damage. Abstract : Vernal freezes are likely to become more frequent with climate change, yet the effects of freeze events on plants and their interactions with insects have received little attention. This paper examines how the interplay of vernal freeze damage and genetic variation in a hardwood tree species influences growth, phytochemistry, and interactions with an insect herbivore. Acute freeze damage dramatically increased sapling mortality, and surviving trees exhibited reduced growth, altered biomass distribution, altered phytochemistry, and supported 2× faster aphid population growth. Our study demonstrates that a single damaging vernal freeze event can alter tree–insect interactions in a dominant forest species through effects on plant growth and chemistry, and that genotypic differences in tree responses to freeze damage may alter the genetic structure of tree populations.