Gas exchange of Ginkgo biloba leaves at different CO 2 concentration levels

Abstract

One and a half year-old Ginkgo saplings were grown for 2 years in 7 litre pots with medium fertile soil at ambient air CO 2 concentration and at 700 μmol mol −1 CO 2 in temperature and humidity-controlled cabinets standing in the field. In the middle of the 2nd season of CO 2 enrichment, CO 2 exchange and transpiration in response to CO 2 concentration was measured with a mini-cuvette system. In addition, the same measurements were conducted in the crown of one 60-year-old tree in the field. Number of leaves/tree was enhanced by elevated CO 2 and specific leaf area decreased significantly. CO 2 compensation points were reached at 75–84 μmol mol −1 CO 2. Gas exchange of Ginkgo saplings reacted more intensively upon CO 2 than those of the adult Ginkgo. On an average, stomatal conductance decreased by ∼30% as CO 2 concentration increased from 30 to 1000 μmol mol −1 CO 2. Water use efficiency of net photosynthesis was positively correlated with CO 2 concentration levels. Saturation of net photosynthesis and lowest level of stomatal conductance was reached by the leaves of Ginkgo saplings at >1000 μmol mol −1 CO 2. Acclimation of leaf net CO 2 assimilation to the elevated CO 2 concentration at growth occurred after 2 years of exposure. Maximum of net CO 2 assimilation was 56% higher at ambient air CO 2 concentration than at 700 μmol mol −1 CO 2.