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Evaluation of a Porous Tube Hydroponics System as a Test Bed for Remote Sensing Instrumentation.    Nirav N. Shah1*, T.W. Dreschel, Ph.D.2, C.R. Hall3, T.E. Foster3, 1Northwestern University, Evanston, IL,2National Aeronautics and Space Administration, 3The Dynamac Corporation, John F. Kennedy Space Center, FL   

   Accurate detection of plant physiological health indicators such as photosynthetic rates, chlorophyll pigment concentrations, leaf moisture and stomatal conductance are major goals of agriculture, ecological and plant remote sensing research.  In this study, we grew Super-Dwarf wheat (Triticum aestivum, cv. Perigee) on a Porous Tube Plant Nutrient Delivery System developed for use in microgravity environments.  The system allows us to control the amount of water available to the plant root zone by altering the nutrient solution pressures within the porous tubes.  Our objective was to assess the potential for detecting differences in indicators of plant health by growing plants at three different root moisture conditions.  To assess plant health and the potential for utilizing remote sensing to monitor it, we measured percent leaf moisture, plant height growth, photosynthetic rates, photosynthetic quenching, chlorophyll concentrations, fluorescence, and leaf spectral reflectance between 400 and 1000 nm.  Our hypothesis was two fold.  First, we hypothesized that plants grown at varying water potentials would exhibit differences in physiological and morphological measures.   Secondly, we hypothesized that these differences in physiological measurements would be correlated to spectral reflectance.  Differences were detected. Plants grown with the most available water had lower photosynthetic rates, greater growth, and higher fluorescence than plants grown with less available water.  Significant correlations between reflectance and photosynthesis at a light level of 1000 mmols photons m-2 s-1 were found in the wavelengths associated with green and yellow visible light along with wavelengths associated with fluorescence.