LAUSR

Premise of research. The serpentine grassland system provides the opportunity to examine whether drought response traits may have contributed to differentiation in the stress-tolerant genus Clarkia. Commonly utilized drought responses might be indicative of traits important to species diversification in stressful environments. Methodology. We examined the drought response strategies of populations of Clarkia gracilis (Onagraceae) from both serpentine and nonserpentine soils. Physiological, morphological, and biomass data were collected under controlled greenhouse conditions. Pivotal results. Serpentine-derived plants exhibited faster growth and germination rates and larger leaf size than nonserpentine-derived plants under increasing water stress, indicating drought escape strategies. However, serpentine-derived plants also employed dehydration avoidance by increasing their water-use efficiency (decreased transpiration rate) under drought stress. In terms of biomass, serpentine-derived plants had a higher fitness potential than nonserpentine-derived plants. Nonserpentine-derived plants tended toward dehydration avoidance through decreased growth rate, decreased transpiration, and smaller leaf size. Conclusions. Our data support transpiration rate as a trait important to stress tolerance. Moreover, serpentine-derived plants avoid drought with drought escape strategies more than nonserpentine plants and may have a higher fitness potential, particularly in water-limiting conditions. Thus, serpentine populations may be competitively superior to nonserpentine populations under drought stress conditions.