Large Daily Variation in $^{13}C-Enrichment$ of Leaf-Respired CO₂ in Two Quercus Forest Canopies

• Published in: The New phytologist Vol. 167; no. 2; pp. 377 - 384
• Main Authors: Hymus, Graham J., Maseyk, Kadmiel, Valentini, Riccardo, Yakir, Dan
• Format: Journal Article
• Language: English
• Published: Blackwell Science 01.08.2005
• Subjects: Carbon dioxide; Carbon isotopes; Flasks; Forest canopy; Fractionation; Leaves; Lipids; Photoperiod; Plants; Rapid Reports; Respiration
• ISSN: 0028-646X; 1469-8137

$\bullet$ The use of the $^{13}C : ^{12}C$ isotopic ratio (δ13C) of leaf-respired CO2 to trace carbon fluxes in plants and ecosystems is limited by little information on temporal variations in δ13C of leaf dark-respired $CO_2 (\delta^{13}C_r$) under field conditions. $\bullet$ Here, we explored variability in $\delta^{13}C_r$ and its relationship to key respiratory substrates from collections of leaf dark-respired CO2, carbohydrate extractions and gas exchange measurements over 24-h periods in two Quercus canopies. $\bullet$ Throughout both canopies, $\delta^{13}C_r$ became progressively $^{13}C-enriched$ during the photoperiod, by up to $7\textperthousand$, then 13C-depleted at night relative to the photoperiod. This cycle could not be reconciled with δ13C of soluble sugars ($\delta^{13}C_{ss}$), starch ($\delta^{13}C_{st}$), lipids ($\delta^{13}C_l$), cellulose ($\delta^{13}C_c$) or with calculated photosynthetic discrimination (Δ). However, photoperiod progressive enrichment in $\delta^{13}C_r$ was correlated with cumulative carbon assimilation (r2 = 0.91). $\bullet$ We concluded that there is considerable short-term variation in $\delta^{13}C_r$ in forest canopies, that it is consistent with current hypotheses for 13C fractionation during leaf respiration, that leaf carbohydrates cannot be used as surrogates for $\delta^{13}C_r$, and that diel changes in leaf carbohydrate status could be used to predict changes in $\delta^{13}C_r$ empirically.