SUN-SHADE ADAPTABILITY OF THE RED MANGROVE, RHIZOPHORA MANGLE (RHIZOPHORACEAE) - CHANGES THROUGH ONTOGENY AT SEVERAL LEVELS OF BIOLOGICAL ORGANIZATION

Rhizophora mangle L., the predominant neotropical mangrove species, oc cupies a gradient from low intertidal swamp margins with high insolati on, to shaded sites at highest high water. Across a light gradient, R, mangle shows properties of both ''light-demanding'' and ''shade-toler ant'' species, and defies designation according to existing succession al paradigms for rain forest trees. The mode and magnitude of its adap tability to light also change through ontogeny as it grows into the ca nopy. We characterized and compared phenotypic flexibility of R. mangl e seedlings, saplings, and tree modules across changing light environm ents, from the level of leaf anatomy and photosynthesis, through stem and whole-plant architecture. We also examined growth and mortality di fferences among sun and shade populations of seedlings over 3 yr. Sun and shade seedling populations diverged in terms of four of six leaf a natomy traits (relative thickness of tissue layers and stomatal densit y), as well as leaf size and shape, specific leaf area (SLA), leaf int ernode distances, disparity in blade-petiole angles, canopy spread:hei ght ratios, standing leaf numbers, summer (July) photosynthetic light curve-shapes, and growth rates. Saplings showed significant sun/shade differences in fewer characters: leaf thickness, SLA, leaf overlap, di sparity in blade-petiole angles, standing leaf numbers, stem volume an d branching angle (first-order branches only), and summer photosynthes is. In trees, leaf anatomy was insensitive to light environment, but l eaf length, width, and SLA, disparities in blade-petiole angles, and s ummer maximal photosynthetic rates varied among sun and shade leaf pop ulations. Seedling and sapling photosynthetic rates were significantly depressed in winter (December), while photosynthetic rates in tree le aves did not differ in winter and summer. Seasonal and ontogenetic cha nges in response to light environment are apparent at several levels o f biological organization in R. mangle, within constraints of its arch itectural bauplan. Such variation has implications for models of stand carbon gain, and suggest that response flexibility may change with pl ant age.