Serpentine populations of Arabidopsis lyrata ssp. lyrata show evidence for local adaptation in response to nickel exposure at germination and during juvenile growth

- Serpentine populations of Arabidopsis lyrata show local adaptation to Ni.
- Serpentine populations have Ni tolerance while non-serpentine populations do not.
- The most tolerant populations have reduced Ni uptake in the leaves and roots.
- Tolerant populations have constitutively high phenolics in the leaves.
- Shoot Ca:Mg ratio was increased in all populations in response to Ni.

Evolutionary divergence among disjunct populations that encounter different stressful conditions may be rapid due to limited gene flow. Arabidopsis lyrata ssp. lyrata (L.) O'Kane & Al-Shehbaz grows throughout the mid-Atlantic region in a variety of fragmented and stressful environments, including serpentine soils. The purpose of this study was to investigate the differential responses to heavy metals (particularly nickel and chromium, naturally occurring in serpentine soils) among three serpentine populations compared to two non-serpentine populations of A. l. ssp. lyrata, as evidence of local adaptation. The five populations were exposed to a nickel, chromium or control treatment during germination and juvenile growth. None of the populations had a negative growth response to chromium. All five populations had reductions in growth when exposed to nickel. The greatest reductions were found in the two non-serpentine populations, which had reductions of 97-99% compared to the control. In contrast, the three serpentine populations had reductions of 23-83%, with most reduction in one of the serpentine populations (Robert E. Lee). Compared to the non-serpentine populations and the least tolerant serpentine population, the two most tolerant serpentine populations (Pilot and Soldiers Delight) had early lateral root formation, accumulated less nickel in their shoots and roots, and had high shoot phenolics. All three serpentine populations had increased serine levels in response to nickel and chromium. The tolerance mechanisms we found in the most tolerant serpentine populations serve as evidence for local adaptation to nickel stress in the non-hyperaccumulator A. l ssp. lyrata.