Population Differentiation for Abscisic Acid Responsiveness inImpatiens capensis(Balsaminaceae)

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Abstract
To test for population differentiation in sensitivity to abscisic acid (ABA) in jewelweed (Impatiens capensis), we experimentally manipulated soil water availability and sprayed ABA on inbred lines derived from sites with different water availabilities. Response to these treatments was quantified with both morphological and physiological measurements, including water use efficiency (WUE). Plants from a relatively dry site in Rhode Island responded to drought treatment by significantly increasing survivorship in subsequent drought compared with plants from a wet site. ABA treatment of the “dry” population plants increased WUE; however, ABA application did not significantly affect WUE in “wet” population plants. Wet‐population plants were also limited by a trade‐off between fruit production and drought survivorship. Additionally, regardless of treatment, wet‐population plants had lower survivorship than dry‐population plants. These environment‐specific responses to water stress provide strong evidence for adaptive differentiation between populations of I. capensis.