Tree-Ring Analysis and Genetic Associations Help to Understand Drought Sensitivity in the Chilean Endemic Forest of Nothofagus macrocarpa

Abstract

Extreme drought events have increased in frequency during the 20th century triggered by global change. Thus, understanding tree-growth resilience across different terrestrial biomes has become a key goal in forest ecology. Here, we evaluate the tree-growth resilience to severe drought in the only Mediterranean-type Ecosystems of South America, using five isolated populations of Nothofagus macrocarpa. For each tree, in each sampling site, we obtained wood cores and fresh leaves for dendrochronological and population genetic analysis, respectively. An evaluation was conducted on growth resilience components in response to the most extreme drought of the 20th century in central Chile (i.e., 1968, with ∼80% of rainfall deficit), and the influence of genetic variability, biogeography, and tree size. We hypothesize that even though current remnant populations of N. macrocarpa are small and isolated, they have locally withstood changes in climate, and that they will be genetically diverse and have a high resilience to extreme droughts. We used nuclear microsatellite markers to estimate tree genetic variability in N. macrocarpa and investigate its correlation with phenotypic traits. We found a higher resistance in the two southernmost populations (mesic sites) than in the three northern populations (xeric sites), however those three xeric populations showed a higher recovery. In addition, a significant clear positive linear correlation between precipitation and resistance, and a negative recovery and relative resilience of tree growth to the extreme drought event of 1968 can be seen. High diversity for simple sequence repeats (SSR) markers was observed, although no population structure was inferred. Southern populations had a higher number of private alleles, which may be an indication of their long-lasting persistence under mesic conditions. Therefore, differences in resilience components are mainly explained by tree size and sites influences, but not genetic diversity. We concluded that observed differences in tree-growth resilience among sites can be explained by a great deal of phenotypic plasticity, fostered by genetically diverse gene pools. We advocate for a genome-wide analysis (i.e., SNP) so as to identify genomic regions correlated with phenotypic traits in order to improve the understanding of the evolutionary processes that shaped this forest resilience over time.

Tree-Level Growth Patterns and Genetic Associations Depict Drought Legacies in the Relict Forests of Abies marocana

“…It is widely acknowledged that tree-ring analysis provides past forest growth conditions at the annual resolution, as well as several important insights on tree sensitivity and adaptive capacity [ 9 , 10 , 11 ]. However, studies with natural populations which combine genomic and dendrophenotype data at the individual level are still scarce, i.e., [ 29 , 30 , 31 , 32 , 33 , 36 ]. Nevertheless, some results indicate that susceptibility to drought could be determined at the genomic level.…”

“…Vásquez et Rodr. ], found no relationship between growth patterns and genetic diversity [ 33 ]. In this case, tree genetic variability was estimated by nuclear microsatellite markers, which might reflect the limitations of methods such as simple sequence repeats (SSR) markers to account for genotype–phenotype associations [ 27 , 28 ].…”

“…Here, we obtained two associations with DBH but none with age supporting a size effect. Previous studies have also shown differences in growth responses to drought mainly explained by tree size [ 33 ]. Moreover, the variability (here estimated by the CV) in tree growth provides an additional piece of evidence about tree growth response to stress related to the SNPs analyzed.…”

“…Indeed, there is still no agreement on the relationship between individual genetic diversity and tree growth, with positive relationships [ 24 , 25 , 26 ] or no associations [ 27 , 28 ]. Recently, the combination of genetic and dendroecological data has been proposed as a reliable framework to obtain a new class of phenotypes (dendrophenotypes) for genetic associations [ 29 , 30 , 31 , 32 , 33 ]. Through the investigation of tree rings, dendroecology allows the quantification of climatic constraints that are exerted on trees [ 11 ].…”

Early аnd Late Wood оf Scots Pine under Conditions of Varying Degrees of Lighting

“…An increase in the radial growth of trees after a disturbance is often referred to as a release, because after it, subdominant trees are released from the suppression of dominant trees (Altman, 2020;Carter et al, 2021;Venegas-González et al, 2022). The forest's response to disturbance depends on the magnitude, severity, and type of disturbance, which alter the succession trajectory and productivity of affected forests with significant implications for their future diversity and structure.…”