Harnessing tree-ring phenotypes to disentangle gene by environment interactions and their climate dependencies in a circum-Mediterranean pine.

Background And Aims: Understanding the genetic basis of adaptation and plasticity in trees constitutes a knowledge gap. We linked dendrochronology and genomics [single nucleotide polymorphisms (SNPs)] for a widespread conifer (Pinus halepensis Mill.) to characterize intraspecific growth differences elicited by climate.

Methods: The analysis comprised 20-year tree-ring series of 130 trees structured in 23 populations evaluated in a common garden. We tested for genotype by environment interactions (G × E) of indexed ring width (RWI) and early- to latewood ratios (ELI) using factorial regression, which describes G × E as differential gene sensitivity to climate.

Key Results: The species' annual growth was positively influenced by winter temperature and spring moisture and negatively influenced by previous autumn precipitation and warm springs. Four and five climate factors explained 10 % (RWI) and 16 % (ELI) of population-specific interannual variability, respectively, with populations from drought-prone areas and with uneven precipitation experiencing larger growth reductions during dry vegetative periods. Furthermore, four and two SNPs explained 14 % (RWI) and 10 % (ELI) of interannual variability among trees, respectively. Two SNPs played a putative role in adaptation to climate: one identified from transcriptome sequencing of P. halepensis and another involved in response regulation to environmental stressors.

Conclusions: We highlight how tree-ring phenotypes, obtained from a common garden experiment, combined with a candidate-gene approach allow the quantification of genetic and environmental effects determining adaptation for a conifer with a large and complex genome.