Growth, biomass allocation and photosynthesis of invasive and native Hawaiian rainforest species

Growth, biomass allocation, and photosynthetic characteristics of seedlings of five invasive nonindigenous and four native species grown under differe nt light regimes were studied to help explain the success of invasive speci es in Hawaiian rainforests. Plants were grown under three greenhouse light levels representative of those found in the center and edge of gaps and in the understory of Hawaiian rainforests, and under an additional treatment w ith unaltered shade. Relative growth rates (RGRs) of invasive species grown in sun and partial shade were significantly higher than those for native s pecies, averaging 0.25 and 0.17 g g(-1) week(-1), respectively, while nativ e species averaged only 0.09 and 0.06 g g(-1) week(-1), respectively. The R GR of invasive species under the shade treatment was 40% higher than that o f native species. Leaf area ratios (LARs) of sun and partial-shade-grown in vasive and native species were similar but the LAR of invasive species in t he shade was, on average, 20% higher than that of native species. There wer e no differences between invasive and native species in biomass allocation to shoots and roots, or in leaf mass per area across light environments. Li ght-saturated photosynthetic rates (Pmax) were higher for invasive species than for native species in all light treatments. Pmax of invasive species g rown in the sun treatment, for example, ranged from 5.5 to 11.9 mu mol m(-2 ) s(-1) as compared with 3.0-4.5 mu mol m(-2) s(-1) for native species grow n under similar light conditions. The slope of the linear relationship betw een Pmax and dark; respiration was Steeper for invasive than for native spe cies, indicating that invasive species assimilate more CO2 at a lower respi ratory cost than native species. These results suggest that the invasive sp ecies may have higher growth rates than the native species as a consequence of higher photosynthetic capacities under sun and partial shade, lower dar k respiration under all light treatments, and higher LARs when growing unde r shade conditions. Overall, invasive species appear to be better suited th an native species to capturing and utilizing light resources, particularly in high-light environments such as those characterized by relatively high l evels of disturbance.