Invasive plant species often have higher rates of resource use than natives and are major drivers of ecosystem change. Understanding invasive physiology and ecology is key to preserving Earth’s ecological systems. Few studies provide both phylogenetically and ecologically paired comparisons of natives and invasives and none have directly compared how differences in water use may vary between the daytime and nighttime. We address this question in a glasshouse, common-garden study using five co-occurring species of the Rubus genus collected from eight sites in western Oregon. Included were the invasive R. armeniacus (Himalayan blackberry) and R. laciniatus (cutleaf blackberry), the native blackberry R. ursinus, and the native raspberries R. parviflorus and R. spectabilis.
During the daytime, species differed significantly for maximum photosynthesis, stomatal conductance (g) and transpiration (E) with the invasive species showing 47%, 61%, and 50% higher rates on average than the native species, respectively. Surprisingly, nighttime g and E were not significantly correlated with daytime g and E. At night, invasive species showed low g (<0.02 mol m-2 s-1) and E (<0.2 mmol m-2 s-1) which was similar to R. ursinus but less than half that of the two native raspberries. These results support the hypothesis that invasive species are rapid consumers of resources during the day, but suggest that at night invasive species may be more conservative with resources than native species.