Photorespiration in Green Plants During Photosynthesis Estimated by Use of Isotopic CO(2).

Photosynthetic re-absorption of photorespired CO(2) causes underestimation in measured photorespiration and turnover rate of the substrate for photorespiration. Actual values of photorespiration exceed the measured by a factor greater than 1 + R'(w)/r(p) + [C(L)](x)/(r(p).L(x)). (R'(w) and r(p) are the partial resistances to CO(2) uptake between atmosphere, mesophyll evaporating surface, and photosynthetic sink, respectively; L(x) is the measured flux of photorespired CO(2) and [C(L)](x) is the ambient conc of photorespired CO(2)). In 8 species, 1 + R'(w)/r(p) alone amounted to a correction ranging between 148% and 233%.