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QUANTIFYING BOUNDARY LAYERS TO UNDERSTAND INDIRECT EFFECTS OF MICROGRAVITY ON PLANTS. Michael Zebuhr1, Oscar Monje2, and Gary W. Stutte2  1Davis & Elkins College, Elkins, West Virginia 26241 2Dynamac Corp., Kennedy Space Center, FL 32899

   Understanding, quantifying and controlling boundary layers is a crucial part of growing plants in space. Heat and mass transfer needed for normal metabolism are sustained by molecular diffusion through a boundary layer. Microgravity may indirectly cause plant stress through effects on boundary layers around plant organs (i.e. leaves and roots).  Several experiments were conducted to quantify boundary layers around plant organs using oxygen sensors, canopy temperature transducers, and anemometers. Oxygen consumption rates of wheat roots were determined at various depths of rooting media and the oxygen concentration at these depths was measured at various wind speeds. Generally, increasing wind speed above the roots increased the oxygen concentration of the root zone, which suggests increased mass transfer of gasses at higher wind speed. The canopy boundary layer, quantified as aerodynamic resistance, was determined as a function of wind speed from energy balance measurements. Decreasing wind speeds increased the canopy aerodynamic resistance and the leaves become hotter. These experiments provided baseline data for a future KC-135 (parabolic) flight experiment.

(Supported by SLSTP and RASTA Experiment).