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Gas Exchange Characteristics of Wheat Stands Grown in a Closed, Controlled Environment

NASA Biomedical Operations and Research, Mail Code MD-RES, Kennedy Space Center, FL 32899
Dep. of Plant and Soil Sci., Univ. of Massachusetts, Amherst, MA 01003.

John C. Sager and William M. Knott

NASA Biomedical Operations and Research, Mail Code MD-RES, Kennedy Space Center, FL 32899

^* Corresponding author

Information on gas exchange of crop stands grown in controlled environments is limited, but is vital for assessing the use of crops for human life-support in closed habitats envisioned for space. To studies were conducted to measure gas exchange of wheat stands (Triticum aestivum L. cv. Yecora Rojo) grown from planting to maturity in a large (20 m² canopy area), closed growth chamber. Daily rates of dark-period respiration and net photosynthesis of the stand subsequent CO₂ drawdown in the light (i.e., a closed-system approach). Lighting was provided as a 20-h photoperiod by high-pressure sodium lamps, with canopy-level photosynthetic photon flux density (PPFD) ranging from 500 to 800 µmol m^-2 s^-1 as canopy height increased. Net Photosynthesis rates peaked near 27 µmol CO₂ m^-2 s^-1 at 25 d and then gradually declined with age. Responses to short-term changes in irradiance after canopy closure indicated the stand light compensation point for photyosynthesis to be near 200 µmol m^-2 s^-1 PPFD. Tests in which CO₂ concentration was raised to 2000 µmol mol^-1 and then allowed to draw down to a compensation point showed that net photosynthesis rates dropped sharply with decreasing CO₂. The CO₂ compensation point for photosynthesis occurred near 50 µmol mol^-1 Short-term (24 h) temperature tests showed net photosynthesis at 20 °C 16 °C > 24 °C, while dark-period respiration at 24 °C > 20 °C > 16 °C. Rates of stand evapotranspiration peaked near Day 25 and remained relatively constant until about Day 75, after which rates declined slowly. Results from these tests will be used to model the use of plants for CO₂ removal, 0₂ production, and water evaporation for controlled ecological life support systems propsed for extraterrestrial environments.

Received for publication December 2, 1991.