Oxygen Inhibition of Photosynthesis

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Abstract
The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O2 in the C3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O2/CO2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O2 and CO2 in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O2/CO2 can be increased by increased leaf temperature under constant atmospheric levels of O2 and CO2 (since O2 is relatively more soluble than CO2 with increasing temperature); by increasing the relative levels of O2/CO2 in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O2/CO2 is kept constant, as leaf temperature is increased, by varying the levels of O2 or CO2 in the atmosphere, then the percentage inhibition of photosynthesis by O2 is similar. The decreased solubility of CO2 relative to O2 (decreased CO2/O2 ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O2 under atmospheric conditions with increasing temperature.