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MEASURING CANOPY GAS EXCHANGE RATES IN HYDROPONICALLY GROWN PEANUT (ARACHIS HYPOGAEA L.) AND SWEETPOTATO (IPOMOEA BATATAS L.) UNDER ENHANCED AND AMBIENT CO₂ CONCENTRATIONS.  J.E. Wesley¹, D.R. Hileman² and D.G. Mortley¹.  ¹Dept of Agricultural Sciences, and ²Dept of Biology, Tuskegee University, Tuskegee, AL.

     Peanut and sweetpotato are being evaluated for use in NASA’s Advanced Life Support System (ALS) program.  On extended space missions, these crops will provide food, nutrient and waste recycling, and air revitalization.  In order to predict plant effects on CO₂ and O₂ levels, season-long gas exchange measurements are required.  Previous measurements of single-leaf photosynthetic rates have not correlated well with final yield, indicating that single-leaf sampling does not accurately reflect the complex interactions of leaf age, leaf position and light environment within the developing canopy.  The objective of this study is to design a system for measuring season-long, whole-plant gas exchange rates under ambient and enhanced CO₂ concentrations and to correlate these gas-exchange data with final yield.  An open-flow system was constructed to determine canopy gas exchange rates of hydroponically-grown peanut and sweetpotato under controlled temperature and light conditions.  Carbon dioxide concentrations were maintained at 400 (ambient) and 1000 µmol/mol^-1.  Gas exchange rates were continuously determined based on CO₂ concentrations in air entering and exiting the canopy gas exchange chambers.  Results are expected to show that elevated CO₂ will lead to increases in canopy photosynthetic rates and in final yield, and that final yield will correlate strongly with whole-season total photosynthesis.  This data will be useful for designing ALS systems that maintain suitable atmospheric conditions for human life.  

     (Supported by NASA: NCC9-51.)