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BOUNDARY LAYERS AROUND PLANT LEAF AND ROOT TISSUES DEPEND ON GRAVITY.    O. Monje¹, D.M. Porterfield², and G.W. Stutte¹. ¹Dynamac Corporation, Kennedy Space Center, FL; ²Department of Biological Sciences, University of Missouri-Rolla. 

Changes in the behavior of fluids and gases in space can induce plant stress responses that confound plant spaceflight experiments. Microgravity alters the movement of heat, water vapor, CO₂ and O₂ between plant surfaces and their environment due to the absence of thermally driven, buoyancy dependent convective transport around leaf and root tissues. Based on this reduction of mass transport, we hypothesize that the thickness of boundary layers forming around leaf and root tissues should increase in microgravity. Furthermore, since these are direct physical changes in the gravity dependent behavior of fluids, measurement is amenable to the short periods of microgravity produced on KC-135 parabolic flights. Infrared transducers and a root oxygen bioavailability sensor were used to monitor changes in leaf temperature and rootzone oxygen transport as a function of gravity. Both thermal transport around the aerial leaf tissue and oxygen transport within the rooting matrix decreased in phase with changes in the force of gravity. These direct physical measurements demonstrate that changes in boundary layer conditions can arise in microgravity and suggest that stress-inducing reductions in thermal transfer, transpiration, and metabolic transport of gases (CO₂ and O₂) may occur in space. These effects might be alleviated in microgravity by the use of mechanical forced convection to drive thermal and mass transfer between plant tissues and the surrounding environment. 

(Supported by NASA: NCC10-0027 to GWS, and a Missouri Research Board Grant to DMP.)