RESPONSE OF WHEAT PHOTOSYNTHESIS TO OZONE - EXPOSURE-RESPONSE RELATIONSHIPS ACHIEVED IN GREENHOUSE CHAMBER FUMIGATIONS

Spring wheat was exposed to ozone in greenhouse chambers and net photo synthesis of flag leaves was measured from emergence until senescence. The time course of photosynthesis was characterized by a slight incre ase at the beginning. and a steady decrease with increasing leaf age. Ozone severely enhanced the progress of this time course and shortened the life span of the leaves. Stomatal conductance decreased with incr easing ozone exposure, too, but this did not sufficiently prevent ozon e uptake and premature breakdown of photosynthetic capacity. From the data, photosynthesis response functions were established for ozone exp osure (expressed as cumulative hourly ozone means) and for calculated cumulative ozone uptake.