Adaptation to drought is coupled with slow growth, but independent from phenology in marginal silver fir (Abies alba Mill.) populations

Drought is one of the most important selection pressures for forest trees in the context of climate change. Yet, the different evolutionary mechanisms, and their environmental drivers, by which certain populations become more drought tolerant than others is still little understood. We studied adaptation to drought in 16 silver fir (Abies alba Mill.) populations from the French Mediterranean Alps by combining observations on seedlings from a large scale greenhouse experiment (N=8199) and on adult tress in situ (N=315). In the greenhouse, we followed half-sib families for four growing seasons for growth traits and bud break phenology, and tested their water stress response in a \"drought until death\" experiment. Adult trees in the field were assessed for δ13C, a proxy for water use efficiency and genotyped at 357 SNP loci. SNP data was used to generate a null expectation for trait divergence between populations to detect the signature of selection, and 31 environmental variables to identif...