Effects of regionally applied heating on the respiration of wild type and transgenic soybean (Glycine max) plants grown under ambient and elevated CO2 environments

Abstract

Nocturnal dark respiration (Rn) in wild type and transgenic soybean plants grown at SoyFACE research facility, Illinois, USA under ambient and elevated CO2 conditions was examined in this study. Transgenic plants were transformed to overexpress a key Calvin cycle enzyme sedoheptulose-1,7- bisphosphatase (SBP) which is thought to improve yield in the field by at least 11%. Heating was applied using infrared heaters mounted 1.2 m above the plants in the field during the growing season of 2015 summer and Rn measurements taken for wild type and SBP overexpressors at ambient and elevated CO₂ plots from V4 to R6 developmental stages. The objective was to study the effects of elevated CO₂ of approximately 585 μmol mol^-1 and +3.5 increase in temperature on wildtype and transgenic SBP plants. Measurements were recorded at growth and constant temperature for both varieties. Experimental plants were transferred to a controlled growth chamber at V4 and R6 developmental stages and the temperature responses examined from 15 to 40°C. Specific leaf area (SLA) and its relations to Rn were also determined. Results indicate that SLA decreased significantly relative to control in the wild type and transgenic soybean plants by R6. Differential responses of Rn to ambient and elevated CO₂ treatments were observed in both plants. In addition, results indicate that Rn declined generally in both varieties under elevated temperature. Lower Rn was attributed to temperature acclimation.

Key words: Dark respiration, soybean, ambient CO₂, elevated CO₂, transgenic plant, sedoheptulose-1,7- bisphosphatase (SBP), heating, acclimation.