Fast-growing and poorly shade-tolerant invasive species may exhibit higher physiological but not morphological plasticity compared with non-invasive species

Phenotypic plasticity is one of the important mechanisms relevant to exotic plant invasions, and high plasticity is likely to influence the potential invasiveness of species. Phenotypic plasticity is broadly defined as the ability of organisms to alter their morphological and/or physiological traits in response to varying environments. Morphological and physiological plasticity are thought to have different mechanisms, resource costs and ecological implications. However, our understanding on how morphological and physiological plasticity contribute to invasiveness is still limited. We explored plant growth, morphological and physiological traits to compare the plasticity in response to variations in light availability in phylogenetically related invasive and non-invasive species from South China. We hypothesized that fast-growing and poorly shade-tolerant invasive species may exhibit higher physiological but not morphological plasticity compared with non-invasive species, prompting their successful invasion with variable light resources. On average, the examined invasive species exhibited a higher biomass accumulation under high light conditions than the non-invasive species. The interaction of light and origin had no significant effect on any of the variables in the morphological traits. However, highly significant effects were found in four of the six variables in the physiological traits: the maximum photosynthesis rate, apparent quantum yield, photosynthetic nitrogen use efficiency, and photosynthetic energy use efficiency. In some cases, the invasive species displayed higher physiological but not morphological plasticity than the non-invasive species. However, contrary to the theory, higher overall mean plasticity was not observed in the invasive plants. Our data support the idea that biological invasion is a complicated process and that strong phenotypic plasticity is merely one of the possibilities leading to the successful invasion of exotic plants.