GREAVER, TARA LIN. University of Miami, Department of Biology, PO Box 249118, Coral Gables, Fl 33143. - The effects of reflected light on the anatomy and photosynthesis of Ipomoea pes-caprae (L.) R. BR. (Convolvulaceae), a tropical sand dune vine.
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)