ARS | Publication request: CO2 enrichment and leaf aging down-regulate both maximum rates of Rubisco carboxylation and mesophyll conductance in SoyFACE

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: May 15, 2008
Publication Date: June 23, 2008
Citation: Sun, J., Feng, Z., Leakey, A., Zhu, X., Ort, D.R. 2008. CO2 enrichment and leaf aging down-regulate both maximum rates of Rubisco carboxylation and mesophyll conductance in SoyFACE [abstract]. American Society of Plant Biologists Annual Meeting. Paper No. P03008. Available: http://abstracts.aspb.org/pb2008/public/P03/P03008.html.

Technical Abstract: Several soybean cultivars were grown under 2 levels of CO2, the ambient level of 370 microbar versus the elevated level of 550 microbar, in SoyFACE (Free Air CO2 Enrichment) in 2007. The responses of CO2 assimilation to CO2, leaf chlorophyll fluorescence, leaf contents of chlorophyll and carotenoids, and leaf mass area (LMA) were investigated at the reproductive R5 stage versus R6 stage. LMA was 4% higher in the plants grown under elevated CO2 versus ambient CO2. The contents of Chla, Chlb and carotenoids decreased 8%, 5%, and 12% in the plants grown under elevated CO2 versus ambient CO2, and decreased 36%, 10% and 18% in R6 versus R5, respectively, indicating significant senescence occurred at R6 stage and elevated CO2 accelerated the senescence in the absence of drought. The A/Ci responses were analyzed and compared using various methods (Harley et al, 1992; Long and Bernacchi, 2003; Ethier et al, 2004, 2006; Sharkey et al, 2007). The transition Ci between Rubisco-limited and RuBP-limited photosynthesis increased 24% under elevated CO2 versus ambient CO2, and increased 14% in R6 versus R5. The maximum rates of electron transport Jmax decreased 18% in R6 versus R5, but was similar between CO2 treatments. The respiration rates in the light Rd decreased 15% in R6 versus R5. Rd under elevated CO2 increased in R5, but decreased in R6 instead. CO2 compensation points (gamma) were significant different among cultivars. In addition, gamma increased under elevated CO2 versus ambient control, and increased in R6 stage versus R5 stage. The maximum rates of carboxylation (Vc,max) and mesophyll conductance (gm) decreased due to leaf aging and elevated CO2. Our results also showed that the sensitivity of Vc,max and gm to transition Ci varied among various methods.