Temperature responses are a window to the physiology of dark respiration: differences between CO 2 release and O 2 reduction shed light on energy conservation

We showed that temperature responses of dark respiration for foliage of Pinus radiata could be approximated by Arrhenius kinetics, whereby E 0 determines shape of the exponential response and denotes overall activation energy of respiratory metabolism. Reproducible and predictable deviation from strict Arrhenius kinetics depended on foliage age, and differed between R CO2 and R O2 . Inhibition of oxygen reduction ( R O2 ) by cyanide (inhibiting COX) or SHAM (inhibiting AOX) resulted in reproducible changes of the temperature sensitivity for R O2 , but did not affect R CO2 . Enthalpic growth – preservation of electrons in anabolic products – could be approximated with knowledge of four variables: activation energies ( E 0 ) for both R CO2 and R O2 , and basal rates of respiration at a low reference temperature ( R REF ). Rates of enthalpic growth by P. radiata needles were large in spring due to differences between R REF of oxidative decarboxylation and that of oxygen reduction, while overall activation energies for the two processes were similar. Later during needle development, enthalpic growth was dependent on differences between E 0 for R CO2 as compared with R O2 , and increased E 0 ( R O2 ) indicated greater contributions of cytochrome oxidase to accompany the switch from carbohydrate sink to source. Temperature‐dependent increments in stored energy can be calculated as the difference between R CO2 ▵ H CO2 and R O2 ▵ H O2 .