Genomic insights into climate change-induced forest dieback in Abies alba hotspots of decline

Abstract

Understanding adaptive genetic responses to climate change is an issue of utmost importance to improve conservation policies and adaptive management. This study deeps on it, focusing on rear-edge silver fir (Abies alba) forests, where decline has been reported and linked to climatic stressors, such as warming and recurrent drought events. Hotspots and coldspots of forest decline and mortality were defined. Different sets of single nucleotide polymorphisms (SNPs), namely genome-wide and adaptive, were used to study their genetic characteristics, aiming to identify differences in genetic diversity between vigor classes (declining and non-declining trees) and age cohorts (adult trees and saplings). Global DNA methylation levels were assessed to investigate a possible role of epigenetic processes in adaptation to stressful environments. Parentage and relatedness analysis were conducted to track the genetic lineage of trees from each site. Our findings indicate that, even though adaptive SNPs seem to provide more insightful information than the genome-wide set, the optimal approach for evolutionary studies is a combination of both. Changes in adaptive genomic diversity and DNA methylation were observed between vigor classes, revealing the existence of a molecular basis behind the ongoing decline events in silver forests. Besides, trees’ relatives display a higher mixture of origins in coldspots, which could provide a temporary refuge for the species’ genetic diversity and adaptive potential. All in all, both genetic and epigenetic characteristics should be considered in order to comprehend how forest trees respond to climate stress to achieve adaptation to climate change.