Measurement of lightdependent photosynthetic carbon fixation

On the basis of an equimolecular photosynthetic quotient (PQ~ 1), the light efficiency of photosynthesis could be calculated from the oxygen evolution data to be ~5.0mgC (mg chla)-1 (mol photon)-1 m2. This is actually below the average of a large number of extrapolated values, which fall mainly in the range 6-18 mg C (mg chla)-1 (mol photon)-1 m2 (Harris, 1978). However, for over 50 years now, it has been possible to work directly in the currency of carbon, applying the so-called 14C method of Steemann Nielsen (1952)

Table 3.1 Temperature-sensitive characteristics of light-dependent carbon fixation. For reported data on maximum photosynthetic rates (Pmax) and on the onset of light saturation (Ik), the majority of observations fall within the ranges shown in the brackets; extreme values are shown outside the brackets. Under conditions of light limitation (Iz < Ik), temperature dependence of photosynthesis is weaker and the single range of photosynthetic efficiencies applies to the available data

Pm in mg C (mg chla) 1 0 2-5 °C 0 17-20°C 0 27-30°C

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