PARENT SESSION
Oral Session #31: Plant Ecology: Gas Exchange.
Presiding: R. Montgomery
Tuesday, August 6. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Isotopic fractionation of ¹³C during respiration in Helianthus annuus.

Ocheltree, Troy^*,1, Marshall, John¹, Black, R. Alan², ¹ University of Idaho, Moscow, ID² Washington State University, Pullman, WA

ABSTRACT- We investigated the possible respiratory fractionation in sunflowers by comparing the ¹³C of CO₂ respired from whole-plant tissue to the extracted starch and sucrose. There was no difference between the ¹³C values of the starch and sucrose extracted from whole-plant tissue (p=0.46). We found a respiratory fractionation ranging from 2.2-5.7‰ across all treatments. The respired CO₂ was always enriched in ¹³C compared to the respiratory substrate. An enrichment of the CO₂ released during respiration should lead to a depletion of the residual carbon used for tissue construction. This theory is supported by our results, as whole-plant tissue was 2.2-3.0‰ depleted compared to respiratory substrate. We measured respiratory fractionation in plants grown under four light intensities in order to test the effect of growth rate on the magnitude of fractionation. The magnitude of respiratory fractionation was negatively correlated with specific growth rate (p=0.0001, r²=0.32). Our results suggest that there is a respiratory fractionation as substrate is converted into whole-plant tissue in sunflowers.

KEY WORDS: respiratory fractionation, ¹³C, respiration