Temperature dependence of two parameters in a photosynthesis model

The temperature dependence of the photosynthetic parameters V-cmax, the maximum catalytic rate of the enzyme Rubisco, and J(max), the maximum electron transport rate, were examined using published datasets. An Arrehenius equation, modified to account for decreases in each parameter at high temperatures, satisfactorily described the temperature response for both parameters. There was remarkable conformity in V-cmax and J(max) between all plants at T-leaf < 25 °C, when each parameter was normalized by their respective values at 25 °C (V-cmax0 and J(max0)), but showed a high degree of variability between and within species at T-leaf > 30 degreesC. For both normalized V (cmax) and J (max) , the maximum fractional error introduced by assuming a common temperature response function is < +/- 0.1 for most plants and < +/- 0.22 for all plants when T-leaf < 25 °C. Fractional errors are typically < +/- 0.45 in the temperature range 25-30 degreesC, but very large errors occur when a common function is used to estimate the photosynthetic parameters at temperatures > 30 degreesC. The ratio J(max) /V-cmax varies with temperature, but analysis of the ratio at T-leaf = 25 degreesC using the fitted mean temperature response functions results in J (max0)/V-cmax0 = 2.00 +/- 0.60 (SD, n = 43).