The genomics and physiology of abiotic stressors associated with global elevational gradients in <i>Arabidopsis thaliana</i>

Phenotypic and genomic diversity in Arabidopsis thaliana may be associated with adaptation along its wide elevational range, but it is unclear whether elevational clines are consistent among different mountain ranges. We took a multi-regional view of selection associated with elevation. In a diverse panel of ecotypes, we measured plant traits under alpine stressors (low CO₂ partial pressure, high light, and night freezing) and conducted genome-wide association studies. We found evidence of contrasting locally adaptive regional clines. Western Mediterranean ecotypes showed low water use efficiency (WUE)/early flowering at low elevations to high WUE/late flowering at high elevations. Central Asian ecotypes showed the opposite pattern. We mapped different candidate genes for each region, and some quantitative trait loci (QTL) showed elevational and climatic clines likely maintained by selection. Consistent with regional heterogeneity, trait and QTL clines were evident at regional scales (c. 2000 km) but disappeared globally. Antioxidants and pigmentation rarely showed elevational clines. High elevation east African ecotypes might have higher antioxidant activity under night freezing. Physiological and genomic elevational clines in different regions can be unique, underlining the complexity of local adaptation in widely distributed species, while hindering global trait-environment or genome-environment associations. To tackle the mechanisms of range-wide local adaptation, regional approaches are thus warranted.