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

Citation

Csillery, Katalin; Buchmann, Nina; Fady, Bruno (2020), Adaptation to drought is coupled with slow growth, but independent from phenology in marginal silver fir (Abies alba Mill.) populations, Dryad, Dataset, https://doi.org/10.5061/dryad.f4qrfj6t3

Abstract

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 identify the selective environment. We found that seedlings originating from populations with low soil water capacity grew more slowly, attained a smaller stature, and resisted the water stress treatment for a longer period of time in the greenhouse. Additionally, adult trees of these populations exhibited a higher water use efficiency as evidenced by δ13C. These results suggest a correlated evolution of the growth-drought tolerance trait complex. Population divergence in bud break phenology was adaptive only in the second growing season, and evolved independently from the growth-drought tolerance trait complex. Adaptive divergence in bud break phenology was principally driven by the inter- and intra-annual variation in temperature at the geographic origin of the population. Our results illustrate the different evolutionary strategies used by populations to cope with drought stress at the range limits across a highly heterogeneous landscape, and can be used to inform assisted migration programs.

Funding

H2020 Marie Skłodowska-Curie Actions, Award: FORGENET