Soybean Canopy Gas Exchange Rates : Effects of Lighting

抄録

Gas exchange rates for 20-m² soybean (Glycine max [L.] Merr.) stands were tracked throughout growth and development in three separate experiments with different photosynthetic photon fluxes (PPF) levels. Canopy photosynthesis and transpiration rates increased in all three experiments 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 DAP) and reached a maximum ca. 30 to 40 DAP. Photosynthetic rates showed a linear increase with growth PPF levels in the three experiments, as well as during short-term 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 the rates gradually decreased.