Document: KIM-3-89-18

The optics, pigments and phenology of water lily leaves.

WHITMAN, K.J.* and J.F.SCHALLES

Creighton University, Omaha, NE 68178 USA 1

Abstract:
Recently, hyperspectral measurements have been used to relate leaf optics and pigment concentrations in higher plants. Our study investigated the optical and pigment relationships in aquatic vegetation. Water lilies may dominate wetland and lentic littoral communities and strongly effect the radiant and geochemical processes. We grew tropical and northern water lily plants in greenhouse tanks and measured leaf phenology and turnover, spectral reflectance and transmission, and pigment content. As the leaves matured, they underwent significant color changes from a red-green or light green early phase to a dark green mature phase and then senesced to yellow. We were able to measure these orderly changes in the leaf optics as the leaf aged. VIS reflectance increased and the "red edge" transition decreased sharply during later stages. Chlorophyll a content varied from 1 mg / cm-2 in yellow senescent leaves to 10-20 mg / cm-2 in young leaves to 25-45 mg / cm-2 in mature leaves. Recent NIR chlorophyll retrieval algorithms (ratio of reflectances at 750 over 700nm and 750 over 550nm) by Gitelson and Merzlyak (1997) accurately related light reflectance to pigment content in our leaves. Further analysis of the reflectance spectra showed a correlation between the red region (Rred) and anthocyanin content. For comparison, measurements were taken from naturally growing specimens in the family Nymphaeaceae. Nuphar lutea subspecies orbiculata were sampled from the St. Mary's River and Nymphaea odorata were collected from the Okefenokee Swamp, both in Southern Georgia. At Lake Manawa, Iowa, we took measurements from American lotus plants, Nelumbo lutea. Compared to the greenhouse plants grown under controlled conditions, the naturally growing plants have shown differences in leaf pigments and thickness, and natural variations to seasonal light and temperature regimes. This study provides a small-scale experimental model that can lead to canopy and habitat studies of wetland communities.

Keywords: Remote Sensing, Water Lilies

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This abstract is being presented at: 3:45 PM in session:
Oral Session #64: Remote Sensing.