The rate of electron transport through PSII [Je(PSII)] was measured as described by Harley et al. [23]. The rate of oxygenation (Vo) and carboxylation (Vc) by Rubisco were estimated as described by von Caemmerer and Farquhar [17]. Under atmospheric conditions, the electron fluxes in the two cycles [Je(PCR) and Je(PCO)] can be measured as described by Krall and Edwards [24]. An alternative flux, Ja, caused by electrons not used by the PCR and/or PCO cycles in the total electron flux driven by PSII, can be estimated from Je(PSII) − Je(PCR + PCO) [25]. Ja(O2-dependent) was estimated
based on the differences between Ja (20% O2) and Ja (2% O2) [25].