EFFECTS OF FREE-AIR CO2 ENRICHMENT ON THE LIGHT RESPONSE CURVE OF NETPHOTOSYNTHESIS IN COTTON LEAVES

Daytime measurements of leaf CO2 exchange rates in a free-air CO2 enri chment (FACE) experiment reveal that at photosynthetically active radi ation (PAR) flux rates in excess of 1000 mumol m-2 s-1, cotton leaves exposed to an atmospheric CO2 concentration of approximately 500 mumol mol-1 exhibit net photosynthetic rates about 30% greater than those f or leaves of similar plants growing in ambient air. As PAR flux rates drop below this value, the stimulatory effect of elevated CO2 rises, s uggesting that the relative benefits of atmospheric CO2 enrichment wil l be greater for shaded cotton leaves that for those exposed to full s unlight.