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IMPACT OF ELEVATED ROOT ZONE TEMPERATURE ON Brassica rapa cv. ASTROPLANT GERMINATION AND DEVELOPMENT.  K.M. Stolp and R.C.Morrow.  Orbital Technologies Corporation, Madison, WI.

     The Biomass Production System (BPS) was developed to support plant growth and experimentation onboard shuttle and the International Space Station (ISS).  The BPS is a four chambered environmental control unit that allows the user to control humidity, light levels, nutrient supply, CO₂, and temperature separately in each of the chambers.  Currently BPS experiments are supporting the growth of Brassica rapa cv. ASTROPLANT and Triticum aestivum cv. Apogee in anticipation of delivery to the ISS in 2002. During a 24-Day Science Verification Test poor germination of B. rapa was observed. After investigating possible causes for the poor germination, including nutrient delivery fluid pressure control, root-zone temperature and chamber CO₂ levels, it was determined that germination and development were adversely affected by excessive evaporation at the soil/air interface.  The increased evaporation resulted from the elevated temperature differential between root and shoot temperatures when the BPS was operating in a hot ambient environment. Further testing showed that raising the relative humidity of the chamber to 90% offset poor germination and development. Following the SVT, a BPS Muffler Performance Test yielded healthy plants that exceeded success criteria.  However, during the performance of a subsequent Mission Verification Test (MVT), poor development of B. rapa was observed.  This was linked to the height of the BPS root/shoot barrier air diffuser being used. Tests are being performed to investigate the performance of B. rapa with 1.2cm and 2.1cm high air diffusers. Seedlings rise above the barrier and are exposed to airflow from under their leaves. Preliminary data shows that percent germination is increased by 20% and mean height is increased by 1.5cm when higher air diffusers are used.