Subtle precipitation differences yield adaptive adjustments in the mesic Nothofagus dombeyi

Abstract

Climate change is impacting on natural systems and forests worldwide have suffered from massive mortality due to extreme droughts. That is the case of mesic Nothofagus dombeyi forests of northern Patagonia, whereas no climate-driven mortality was recorded towards drier areas. The aim was to examine population differences in relation to a small precipitation gradient at morphological, physiological, and genetic scales. Adaptive differences between seedlings collected from dry and mesic sites of N. dombeyi on the eastern slopes of the Andes were studied combining common garden and water stress manipulative experiments with genomic analyses. We recorded mortality, plant architectural and leaf traits during cultivation in the greenhouse. A set of plants were subjected to water deficit experiments and water potential was measured. Genomic differences were analyzed by Single Nucleotide Polymorphisms (SNPs). Plants from the mesic site grew taller with more branches and number of larger leaves, and greater stomatal density under optimum conditions yet with slightly more negative midday water potentials due to induced desiccation. Adaptive SNPs yielded similar divergence than quantitative traits which were greater than that of neutral SNPs. Five adaptive loci had a significant association to whole plant and leaf traits. These results show that in spite of the small climatic differences between sites and continuous gene flow populations showed adaptive adjustments and differed significantly in growth, ecophysiology, and genetically. This information can be used in climate-oriented restoration efforts.