FOLIAR SPECTRAL REFLECTANCE AND PLANT STRESS ON A BARRIER-ISLAND

Leaf spectral reflectance was measured in the field to provide estimates of plant stress for a barrier island interior. During summer on Horn Island, Mississippi, visible (400-760 nm wavelengths) reflectance in Myrica cerifera L. was slightly greater on a site that remained flooded compared to an adjacent site that remained relatively dry, indicating only mild stress on the flooded site. This coincided with leaf water potentials, conductances to water vapor diffusion, and foliar element concentrations that were similar between the two sites. Although Na and Cl concentrations were much greater on the island than on a mainland site, visible reflectances and chlorophyll a concentrations indicated that M. cerifera was not stressed in comparison to the mainland. In Pinus elliottii Engelm., greater visible reflectance on the flooded than on the dry island site and on both island sites compared with the mainland indicated appreciable stress. These reflectance responses to the island environment, particularly reflectance increases near 600 nm and 700 nm, were spectrally similar to those reported previously for a variety of environmental conditions that inhibit growth. Infrared (760-2500 nm) reflectance also differed among sites for both species but was less sensitive to the barrier island environment than visible reflectance. Reflectances indicated that M. cerifera was adapted better than P. elliottii to the barrier island environment, particularly in saturated soils.