Ecophysiological responses of woody plants to past CO(2) concentrations

An approach is detailed for calculating historical rates of CO(2) uptake and water loss of leaves from measurements of leaf delta(13)C composition and climatic information. This approach was applied to investigate leaf gas exchange metabolism of woody taxa during the past 200 years of atmospheric CO(2) increase and in response to the longer-term atmospheric CO(2) increases plants experienced over the Pleistocene. Reconstructed net assimilation rates and water use efficiencies increased in response to increasing atmospheric CO(2) concentrations in both sets of material, whereas stomatal conductance, showing the combined responses of changes in stomatal density and leaf assimilation rates, was generally less responsive. Woody temperate taxa maintained a nearly constant c(i)/c(a) ratio in response to the increase in atmospheric CO(2) concentrations over both timescales, in part, as a result of changes in stomatal density. The reconstructed leaf-scale physiological responses to past global climatic and atmospheric change corroborated those anticipated from experimental work indicating the adequate capacity of experiments, at least at the scale of individual leaves, to predict plant responses to future environmental change.