ECOPHYSIOLOGY OF INTRODUCED PENNISETUM-SETACEUM ON HAWAII - THE ROLE OF PHENOTYPIC PLASTICITY

The C-4 African grass, Pennisetum setaceum (fountaingrass), has a greater altitudinal distribution than any other grass on the island of Hawaii. Clones of P. setaceum were reciprocally transplanted among coastal dry grassland, montane dry shrubland, and subalpine dry forest sites on the leeward side of Hawaii to evaluate the contribution of local adaptation and individual tolerance to the broad ecological amplitude of this grass. Physiological, growth, and reproductive responses differed among sites without evidence of local adaptation. Greatest tiller production and the highest photosynthetic rates were observed at the mid-altitude site, but plants at the coastal site attained greater basal areas, aboveground biomass, and number of inflorescences. Correlation among the responses of different plant characters was environmentally dependent, suggesting that the integrated expression of these characters is also plastic. Few differences in plant responses, however, were attributable to a population's origin or the site-by-population interaction; resident populations and introduced populations responded similarly at each site. Furthermore, few characters exhibited variation among clones, indicating that these populations likely possess little genetic variation. Limited clonal variation was, however, detected for net photosynthesis, the ratio of internal to ambient CO2 concentration (c(i)/c(a)), and specific leaf area, but only on two of five dates over a 1-yr period. Phenotypic plasticity for both individual characters and the integration of physiological and morphological characters have apparently been most important in allowing P. setaceum to become dominant across diverse habitats on Hawaii.