ARS | Publication request: Photosynthetic Responses of Poplar and Soybean to Free Air Enrichment of Co2

Submitted to: Plant Physiology Supplement
Publication Type: Abstract
Publication Acceptance Date: July 30, 2003
Publication Date: December 20, 2003
Citation: BERNACCHI, C.J., MORGAN, P.B., ORT, D.R., LONG, S.P. PHOTOSYNTHETIC RESPONSES OF POPLAR AND SOYBEAN TO FREE AIR ENRICHMENT OF CO2. PLANT PHYSIOLOGY SUPPLEMENT. 2003. Abstract p. 92.

Technical Abstract: Numerous efforts have been made to determine how photosynthesis will respond to elevated CO2 concentration ([CO2,e]. In this study, we use gas-exchange techniques to address the effect [CO2,e] will have on light saturated rates of photosynthesis and on the in vivo activities of processes that limit photosynthesis under most conditions: maximum velocity of carboxylation (Vc,max) of Rubisco, and maximum rates of electron transport through photosystem II (Jmax). This research was conducted using the Soybean Free Air CO2 Enrichment (SoyFACE) facility (two soybean cultivars) and the Poplar Free Air CO2 Enrichment (PopFACE) facility (three poplar species). FACE allows open air CO2 enrichment of whole canopies without alterations in microclimate. Soybean and poplar grown in [CO2,e] had higher rates of photosynthesis over the duration of the experiments. A decrease in Vc,max and in the ratio of Vc,max to Jmax was evident for soybean grown in [CO2,e] compared with the control plants and is evidence of a decrease in photosynthetic potential and suggests that soybean shifted resources away from Rubisco content and/or activation. This response is consistent with optimal partitioning of resources away from a process that is no longer limiting in [CO2,e]. Similarly, two of the three poplar species showed photosynthetic down-regulation of Vc,max with growth in [CO2,e], however, there was no clear shift in the Vc,max Jmax ratios for any poplar species. For poplar and soybean, two widely contrasting species, down-regulation of photosynthetic potential to growth in [CO2,e] was apparent, although not sufficient to prevent an overall increase in Amax due to suppression of photorespiration.