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Title: SOYBEAN CANOPY GAS EXCHANGE REATES: EFFECTS OF LIGHTING

Author
item WHEELER, RAYMOND - NASA
item COREY, KENNETH - MILLERS FALLS MA
item Volk, Gayle
item MACKOWIAK, CHERYL - USFS
item NEIL YORIO - NASA
item SAGER, JOHN - NASA

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2004
Publication Date: 7/27/2004
Citation: Wheeler, R., C. Kenneth, G.M. Volk, C. Mackowiak, N.C. Yorio, and J.C. Sager. Soybean canopy gas exchange rates: Effects of lighting. Ecological Engineering 16(3):209-214.

Interpretive Summary: This project measured growth, photosynthesis, and transpiration in soybean canopies under three light levels. Plants were grown hydroponically in a large, sealed chamber. We were able to measure oxygen, carbon dioxide, and transpired water for the entire canopy of plants without disrupting the atmosphere by entering the chamber. Under all lighting levels, the photosynthetic rates and transpiration rates increased as the plants were established between 10 and 30 days after planting. Dark period respiration also increased during stand establishment. Photosynthetic rates increased nearly linearly as the light levels increased, while canopy transpiration rates remained constant. Photosynthetic rates and transpiration rates both decreased as the stands matured, 55 to 90 days after planting.

Technical Abstract: Gas exchange rates for 20-m2 soybean (Glycine max [L.] Merr.) stands were tracked throughout growth and development in three separate studies with different irradiance (PPF) levels in NASA's biomass production chamber. Canopy photosynthesis and transpiration rates increased in all three studies with canopy ground during early growth (10 to 30 days after planting--DAP) and reached a maximum ca. 40 DAP. Dark period respiration rates increased with increasing biomass (10 to 30 days), reaching a maximum ca. 30 to 40 DAP. Photosynthetic rates showed a near linear increase with increased PPF in the three studies, as well as during short-term (1-h) tests in which lamps were dimmed to achieve different PPFs. In contrast, canopy transpiration rates were similar in all three studies. Photosynthesis and transpiration rates both decreased as the stands matured (ca. 55 to 90 DAP), whereas dark period respiration rates remained relatively constant until ca. 75 DAP, after which they gradually decreased.