Advances in measurements and models of photosynthetic carbon isotope discrimination in C₃ plants

Abstract

The scientific community has long recognized that the study of atmosphere-biosphere interactions is vital to understanding fields as varied as agriculture, ecology and global change. Measurements of CO2 and H2O exchange are potentially enhanced by measurements of the minor isotopologues of those species (e.g.

Vapour pressure deficit during growth has little impact on genotypic differences of transpiration efficiency at leaf and whole‐plant level: an example from Populus nigra L.

“…The negative phenotypic correlation found between Δ 13 C ss and assimilation‐weighted diurnal mean TE ( A/g s ) under the two VPD treatments, as well as the difference of A/g s between the two groups of genotypes diverging for 13 C discrimination, confirm that Δ 13 C ss is a reliable indicator of A/g s as predicted by the discrimination model (Farquhar et al . ; Ubierna & Farquhar ) and as reported by different groups (Brugnoli et al . ; Roussel et al .…”

“…The other components of the discrimination model such as mitochondrial respiration and photorespiration have a much smaller and almost negligible impact (Douthe et al . , ; Ubierna & Farquhar ). Therefore, g m is probably the most important contributor to Δ 13 C D , the two parameters being inversely correlated (Pons et al .…”

“…Carbon isotope discrimination predicted by the model ( Δ 13 C sim ) was calculated using Eqn and b = 29‰ (O'Leary ). We computed the difference between Δ 13 C sim and Δ 13 C ss , and weighted it by the ternary correction to obtain Δ 13 C D , which is directly related to the discrimination induced by mesophyll conductance, assuming the discrimination due to respiration and photorespiration remains small (Ubierna & Farquhar ).…”

“…). The discrimination against 13 C during photosynthesis is correlated to C i / C a by the following model that takes a ternary correction of fractionation ( t ) into account (Farquhar & Cernusak ; Ubierna & Farquhar ): where b is the fractionation during carboxylation by rubisco and t the ternary correction factor: where E is the transpiration rate, g ac is the conductance to CO 2 diffusion across the boundary layer and the stomata; and: where a b and a s are the fractionation occurring across the boundary layer and the stomata (2.8 and 4.4‰, respectively), and C a , C s and C i are the CO 2 mole fractions in ambient air, at leaf surface and in intercellular spaces, respectively. The earlier version of the model corresponds to t = 0.…”

“…The difference between the predictions of Eqn and recorded Δ 13 C , weighted by a factor depending on t , is often used to quantify g m (Evans & von Caemmerer ; Pons et al . ; Farquhar & Cernusak ; Ubierna & Farquhar ).…”