OPTIMAL ACCLIMATION OF THE C-3 PHOTOSYNTHETIC SYSTEM UNDER ENHANCED CO2

A range of studies of C-3 plants have shown that there is a change in both the carbon flux and the pattern of nitrogen allocation when plant s are grown under enhanced CO2. This paper examines evidence that allo cation of nitrogen both to and within the photosynthetic system is opt imised with respect to the carbon flux. A model is developed which pre dicts the optimal relative allocation of nitrogen to key enzymes of th e photosynthetic system as a function of CO2 concentration. It is show n that evidence from flux control analysis is broadly consistent with this model, although at high nitrogen and under certain conditions at low nitrogen experimental data are not consistent with the model. Accl imation to enhanced CO2 is also assessed in terms of resource allocati on between photosynthate sources and sinks. A means of assessing the o ptimisation of this source-sink allocation is proposed, and several st udies are examined within this framework. It is concluded that C-3 pla nts probably possess the genetic feedback mechanisms required to effic iently 'smooth out' any imbalance within the photosynthetic system cau sed by a rise in atmospheric CO2.