Are There Functional Differences in Key Photosynthetic Traits Between Native and Non-Native Oenothera drummondii Populations?

Physiological differentiation between native and introduced populations may facilitate establishment across contrasting environments, but it remains unclear whether this reflects a general enhancement of photosynthetic performance. We investigated light-response traits, photosynthetic biochemical capacity and leaf pigment content in three native and three introduced populations of Oenothera drummondii grown under common greenhouse conditions. We measured light-response and A/Ci curves with a LI-6400 system and then analyzed them using the Ye and C3 biochemical models, respectively. Traits were compared using nested ANOVA, with population nested within origin. Light-response traits differed significantly among populations, but no significant differences between origins were detected. Total chlorophyll content also differed among populations, but no significant origin effect was detected, and it was positively correlated with Anmax and Imax across the six populations. Introduced populations had higher net CO2 assimilation at external CO2 concentrations of 400 and 600 µmol mol−1, and higher maximum Rubisco carboxylation and electron-transport capacities. These biochemical capacities did not differ significantly among populations, whereas day respiration showed no significant origin effect. Photosynthetic differentiation therefore involved specific components of photosynthetic performance rather than a uniform enhancement in introduced populations, emphasizing the importance of population-level variation when assessing functional differentiation across geographical ranges.