ECOPHYSIOLOGICAL RESPONSES OF WOODY-PLANTS TO PAST CO2 CONCENTRATIONS

An approach is detailed for calculating historical rates of CO2 uptake and water loss of leaves from measurements of leaf delta(13)C composi tion and climatic information. This approach was applied to investigat e leaf gas exchange metabolism of woody taxa during the past 200 years of atmospheric CO2 increase and in response to the longer-term atmosp heric CO2 increases plants experienced over the Pleistocene. Reconstru cted net assimilation rates and water use efficiencies increased in re sponse to increasing atmospheric CO2 concentrations in both sets of ma terial, whereas stomatal conductance, showing the combined responses o f changes in stomatal density and leaf assimilation rates, was general ly less responsive. Woody temperate taxa maintained a nearly constant c(i)/c(a), ratio in response to the increase in atmospheric CO2 concen trations over both timescales, in part, as a result of changes in stom atal density. The reconstructed leaf-scale physiological responses to past global climatic and atmospheric change corroborated those anticip ated from experimental work indicating the adequate capacity of experi ments, at least at the scale of individual leaves, to predict plant re sponses to future environmental change.