CONICET | Buscador de Institutos y Recursos Humanos

Extreme drought events have increased in frequency during the 20th century triggeredby global change. Thus, understanding tree-growth resilience across different terrestrialbiomes has become a key goal in forest ecology. Here, we evaluate the tree-growthresilience to severe drought in the only Mediterranean-type Ecosystems of SouthAmerica, using five isolated populations of Nothofagus macrocarpa. For each tree, ineach sampling site, we obtained wood cores and fresh leaves for dendrochronologicaland population genetic analysis, respectively. An evaluation was conducted on growthresilience components in response to the most extreme drought of the 20th centuryin central Chile (i.e., 1968, with 80% of rainfall deficit), and the influence of geneticvariability, biogeography, and tree size. We hypothesize that even though currentremnant populations of N. macrocarpa are small and isolated, they have locallywithstood changes in climate, and that they will be genetically diverse and have a highresilience to extreme droughts. We used nuclear microsatellite markers to estimate treegenetic variability in N. macrocarpa and investigate its correlation with phenotypic traits.We found a higher resistance in the two southernmost populations (mesic sites) thanin the three northern populations (xeric sites), however those three xeric populationsshowed a higher recovery. In addition, a significant clear positive linear correlationbetween precipitation and resistance, and a negative recovery and relative resilience oftree growth to the extreme drought event of 1968 can be seen. High diversity for simplesequence repeats (SSR) markers was observed, although no population structure wasinferred. Southern populations had a higher number of private alleles, which may be anindication of their long-lasting persistence under mesic conditions. Therefore, differencesin resilience components are mainly explained by tree size and sites influences, butnot genetic diversity. We concluded that observed differences in tree-growth resilienceamong sites can be explained by a great deal of phenotypic plasticity, fostered bygenetically diverse gene pools. We advocate for a genome-wide analysis (i.e., SNP) soas to identify genomic regions correlated with phenotypic traits in order to improve theunderstanding of the evolutionary processes that shaped this forest resilience over time.

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