OPTIMAL-CONTROL OF GAS-EXCHANGE DURING DROUGHT - EMPIRICAL-EVIDENCE

The optimal regulation model by Makela, Berninger and Hari (Annals of Botany 77: 461-467, 1996) was applied to data for photosynthesis and t ranspiration of Scots pine during a 22-d drought period. There was a c lear decrease in photosynthesis and transpiration during that period. The agreement between model and photosynthesis data was good. The resi duals of photosynthesis were not systematic with respect to temperatur e, irradiance or water vapour deficit. However, the model initially ov erestimated transpiration by 50%, although there was a clear linear re lationship between measured and estimated values. The results suggest that there was no decrease in photosynthetic capacity during the perio d, but a decrease in stomatal conductance was responsible for the chan ges in photosynthesis and transpiration. The observations are similar to results in the literature. (C) 1996 Annals of Botany Company