Responses to light and water availability of four invasive Melastomataceaein the Hawaiian islands

Plant invasion by Neotropical Melastomataceae is prominent in Hawaii. To un derstand life history traits of four successful invasive Melastomataceae, t wo shade-intolerant herbs (Arthrostema ciliatum and Tibouchina herbacea) an d two shade-tolerant woody species (Clidemia hirta, a shrub, and Miconia ca lvescens, a tree) were subjected to three light levels and two watering reg imes in a greenhouse. Plant height, leaf number and area, biomass allocatio n, relative growth rate (RGR), carbon assimilation (A), leaf nutrient conte nt, leaf construction costs (CC), specific leaf mass (SLM), and leaf spectr al properties were determined at the end of the experimental period. Plant size, total biomass, RGR, A, CC, and SLM decreased, whereas leaf light tran smittance and leaf N increased under low light in all species. The effects of water stress were weaker than light-stress effects. Relative growth rate of herbs grown in sun and partial shade (0.046 and 0.033 g g(-1) d(-1), re spectively) was higher than in the woody species (0.027 and 0.020 g g(-1) d (-1)). Woody species allocated more biomass to leaf production than herbs, which allocated more biomass to stem production. Shade increased allocation of biomass to leaves, and water stress increased the root-shoot ratio in a ll species. Partial shade increased leaf area ratios more in the herbs (140 %) than in woody species (68%). Miconia calvescens and C. hirta had higher leaf absorbance (92%) than both herbs (79%). Maximum A under all light trea tments was similar in all species, and there was substantial acclimation to the different light levels. Leaf construction cost was higher-in the appar ently long-lived leaves of the woody species. Relative growth rate, carbon allocation, and SLM showed larger changes to light and water stress than A and related photosynthetic parameters. All species showed responses qualita tively similar to those of other tropical species including the high acclim ation potential to light, but the herbs exhibited the largest quantitative responses. When compared with a large group of native species, the four mel astomes appear to be better suited to capture and use light, which is consi stent with their rapid spread in mesic and disturbed Hawaiian environments.