Leaf ontogenetic dependence of light acclimation in invasive and native subtropical trees of different successional status
In the Bonin Islands of the western Pacific where the light environment is characterized by high fluctuations due to frequent typhoon disturbance, we hypothesized that the invasive success of Bischofia javanica Blume (invasive tree, mid-successional) may be attributable to a high acclimation capacity under fluctuating light availability. The physiological and morphological responses of B. javanica to both simulated canopy opening and closure were compared against three native species of different successional status: Trema orientalis Blume (pioneer), Schima mertensiana (Sieb. et Zucc.) Koidz (mid-successional) and Elaeocarpus photiniaefolius Hook.et Arn (late-successional). The results revealed significant species-specific differences in the timing of physiological maturity and phenotypic plasticity in leaves developed under constant high and low light levels. For example, the photosynthetic capacity of T. orientalis reached a maximum in leaves that had just fully expanded when grown under constant high light (50% of full sun) whereas that of E. photiniaefolius leaves continued to increase until 50 d after full expansion. For leaves that had just reached full expansion, T. orientalis, having high photosynthetic plasticity between high and low light, exhibited low acclimation capacity under the changing light (from high to low or low to high light). In comparison with native species, B. javanica showed a higher degree of physiological and morphological acclimation following transfer to a new light condition in leaves of all age classes (i.e. before and after reaching full expansion). The high acclimation ability of B. javanica in response to changes in light availability may be a part of its pre-adaptations for invasiveness in the fluctuating environment of the Bonin Islands.