Light heterogeneity influences the anatomy and physiology of leaves. In habitats where an overhead canopy is absent (e.g. deserts and dunes) different ground covers reflect light differently, and thus create a mosaic of reflected light. I studied the effects of reflected light on the anatomy and physiology of a tropical sand dune vine, Ipomoea pes-caprae (Convolvulaceae). Ipomoea pes-caprae has a symmetric leaf anatomy, with palisade parenchyma on both the adaxial and abaxial surfaces. Because the leaf anatomy is symmetric, I tested the hypothesis that the adaxial and adaxial surfaces responded independently to local light environment. Sampling was restricted to the six youngest fully expanded leaves, and thereby removed differences in nitrogen content of leaves due to age. Two types of light environments were characterized based on ground cover substrate. In high reflected light (HRL) environments plants grew directly over sand (26%5.2% of incident PAR reflected) and in low reflected light (LRL) environments plants grew over vegetation (6.1% 3.0% of incident PAR reflected). Photosynthetic maxima (Amax) did not differ between the adaxial surfaces in the HRL and LRL treatments (19.0 vs. 17.5 umol photon m-2 m-1, Tukey-Kramer HSD, p<0.05). Amax of abaxial surfaces of leaves in HRL environments was 2.6 times greater than those in the LRL environment (10.4 vs. 4.1 umol photon m-2 m-1, t-test, p<0.05). Palisade parenchyma of abaxial surfaces in HRL was 20% thicker than those in LRL (98.2 vs.79.7 um, t-test, p<0.05). Spongy mesophyll was 30% thicker for leaves growing over LRL than HRL. Leaves of I. pes-caprae demonstrated plasticity in gas exchange and anatomy in response to reflected light level. Presumably, this plasticity is an attribute contributing to its success as a pioneer species of tropical dunes, and successful colonization around the world.

Key words: abaxial photosynthesis, leaf symmetry, nitrogen content, reflected light, sand dune, tropical vine Ipomoea pes-caprae (Convolvulaceae)