Acclimation of photosynthesis to light: a mechanistic approach

1. We developed a mechanistic model to explain acclimation of photosynthesis to the radiation distribution within plant canopies. The model predicts the amount of photosynthetic apparatus in any leaf from the balance between supply of carbohydrates by photosynthesis and the demand for resources by enzyme synthesis and turnover and export to sinks elsewhere in the plant. 2. The turnover of the photosynthetic apparatus is assumed to depend on the amount of available resources: nitrogen and carbohydrates. Leaves export carbohydrates into a common pool of carbohydrates and take nitrogen from the common nitrogen pool, All leaves of one plant are assumed to share these common pools, 3. The model allows description of the dynamics of the acclimation process known to occur within weeks after changes in the environment. The model also adequately explains measured leaf nitrogen distributions and total leaf area in a multispecies canopy. 4. According to our model, differences between species in leaf nitrogen distribution with respect to PPFD can be explained with differences in plant common pools of carbohydrates and nitrogen. 5. Although canopies cannot be treated as a big leaf in a simple way because mechanisms predicting amount of photosynthetic apparatus in a single leaf and in entire canopy are different, total canopy nitrogen can be used as an estimate for canopy total photosynthesis.