Alternative electron fluxes such as the cyclic electron flux (CEF) around photosystem I (PSI) and Mehler reaction (Me) are essential for efficient photosynthesis because they generate additional ATP and protect both photosystems against photoinhibition. The capacity for Me can be estimated by measuring O₂ exchange rate under varying irradiance and CO₂ concentration. In this study, mass spectrometric measurements of O₂ exchange were made using leaves of representative species of C₃ and C₄ grasses grown under natural light (control; PAR ~ 800 µmol quanta m⁻² s⁻¹) and shade (~ 300 µmol quanta m⁻² s⁻¹), and in representative species of gymnosperm, liverwort and fern grown under natural light. For all control grown plants measured at high CO₂, O₂ uptake rates were similar between the light and dark, and the ratio of Rubisco oxygenation to carboxylation (V_o/V_c) was low, which suggests little potential for Me, and that O₂ uptake was mainly due to photorespiration or mitochondrial respiration under these conditions. Low CO₂ stimulated O₂ uptake in the light, V_o/V_c and Me in all species. The C₃ species had similar V_o/V_c, but Me was highest in the grass and lowest in the fern. Among the C₄ grasses, shade increased O₂ uptake in the light, V_o/V_c and the assimilation quotient (AQ), particularly at low CO₂, whilst Me was only substantial at low CO₂ where it may contribute 20–50% of maximum electron flow under high light.

替代电子通量，例如光系统 I (PSI) 和梅勒反应 (Me) 周围的循环电子通量 (CEF) 对于有效的光合作用至关重要，因为它们会产生额外的 ATP 并保护两个光系统免受光抑制。Me 的容量可以通过测量不同辐照度和 CO ₂浓度下的O ₂交换率来估计。在这项研究中，将O质谱测量₂用C的代表性物种的叶作了交换₃和C _4个的自然光下生长的草类（对照; PAR〜800微摩尔量子m ^-2 小号^-1）和阴影（〜300微摩尔量子 m ^-2  s ^-1)，以及在自然光下生长的裸子植物、地衣和蕨类植物的代表性物种。对于在高 CO _{2 下}测量的所有对照生长植物，O ₂吸收率在明暗之间相似，并且 Rubisco 氧化与羧化的比率 ( V _o / V _c ) 低，这表明 Me 的潜力很小，并且O ₂吸收主要是由于这些条件下的光呼吸或线粒体呼吸。在所有物种中，低 CO ₂刺激了光中的O ₂吸收、V _o / V _c和 Me。C ₃物种具有相似的V_o / V _c，但我在草丛中最高，在蕨类植物中最低。在 C ₄草中，遮荫增加了光中的O ₂吸收、V _o / V _c和同化商 (AQ)，特别是在低 CO _{2 时}，而 Me 仅在低 CO _{2 时很重要}，它可能贡献 20-50高光下最大电子流的百分比。