STOMATAL RESPONSES OF THE LIVING FOSSIL GINKGO-BILOBA L. TO CHANGES IN ATMOSPHERIC CO2 CONCENTRATIONS

Leaf stomatal density and index of Ginkgo biloba L. were both signific antly (P < 0.05) reduced after 3 years growth at elevated CO2 (560 ppm ), with values comparable to those of cuticles prepared from Triassic and Jurassic fossil Ginkgo leaves thought to have developed in the hig h CO2 'greenhouse world' of the Mesozoic. A reciprocal transfer experi ment indicated that reductions in stomatal density and index irreversi bly reduced stomatal conductance, particularly at low leaf-to-air vapo ur pressure deficits and low internal leaf CO2 concentrations (C-i). T hese effects probably contributed to the high water-use efficiency of Ginkgo spp. in the Mesozoic relative to those of the present, as deter mined from carbon isotope measurements of extant and fossil cuticles.