Field evidence for the optimality hypothesis of gas exchange in plants

The `optimality hypothesis' of gas exchange in plants has been studied sinc e the 1970s, but testing it in the field has proven difficult. A recent ref ormulation of the hypothesis with detailing assumptions on leaf structure m akes it possible to solve the optimisation problem explicitly, such that th e predictions of gas exchange are readily testable against field data. This form of the model was tested against field measurements of photosynthesis, transpiration and stomatal conductance in Scots pine (Pinus sylvestris) sh oots during three clear summer days. Model parameters were estimated indepe ndently from photosynthesis measurements on preceding days. The measurement s were carried out at a new field measurement station with a very low level of noise. The predictions of photosynthesis, transpiration and stomatal co nductance explained 84-98% of the variance in the data.