Climate-driven adaptive responses to drought of dominant tree species from Patagonia

Abstract

The increase in the frequency and severity of extreme weather events affects populations of tree species. As a result, many forests around the world have suffered massive mortality due to extreme droughts. Therefore, it is important to understand the potential adjustments of dominant woody species of temperate forests to climate change. The objective was to show in seedlings inhabiting the most contrasting habitats, forest types, and precipitation regimes the relevance of species-specific and intra-specific adaptive trait variation. Ecophysiological differences between seedlings collected from distinct humid and dry provenances of Nothofagus pumilio and N. dombeyi in northern Patagonia were assessed using common garden and water stress manipulative experiments. Levels of genetic diversity and divergence were evaluated with microsatellite analysis. Seedlings from humid provenances of both species showed increased growth, and leaf traits differed significantly between N. dombeyi provenances. Studied species behaved differently under water stress, isohydric for N. dombeyi and anisohydric for N. pumilio, while no intraspecific differences were measured in the regulation of water status. Humid provenance of N. dombeyi had higher genetic diversity than the dry one, whereas those of N. pumilio were similarly diverse. Yet, low but significantly different from zero genetic divergence was measured between provenances of the latter. Our results show species-specific responses to water stress and that adaptive variation at distinct provenances has a genetic basis that is maintained despite potential gene flow. The strategy of using seedlings from "regional admixture provenancing" is suggested for long-term management of vulnerable taxa to desiccation as the mesic N. dombeyi.