An analysis of the temperature response curves of CO2 exchange in the leaves of two temperate and one tropical grass species.

The temperature dependence of carbon dioxide exchange in two temperate grass species, Lolium perenne (S.23) and Lolium multiflorum (S.22), and one tropical grass species, Cenchrus ciliaris, have been examined. It has been shown that the decline in the net CO2 exchange rate above the optimum temperature is caused, in the case of C. ciliaris, by denaturation, and, in the case of L. perenne and L. multiforum by the greater response to temperature of respiration compared with photosynthesis.Activation energies have been obtained for both photosynthetic and respiratory systems. For both systems the values fall into discrete groups, and it is postulated that each group may be characteristic of a particular rate-limiting process. The distribution of values changes with changes in experimental conditions, there being marked differences in the distribution of values obtained for light-limited and CO2-limited photosynthesis.