EFFECTS OF ATMOSPHERIC CO2 ENRICHMENT AND FOLIAR METHANOL APPLICATIONON NET PHOTOSYNTHESIS OF SOUR ORANGE TREE (CITRUS-AURANTIUM, RUTACEAE) LEAVES

Foliar spray applications of 40% aqueous methanol were made to sunlit leaves of sour orange trees that had been grown continuously in clear- plastic-wall open-top enclosures maintained out-of-doors at Phoenix, A rizona, for over 5.5 years in ambient air of approximately 400 mu mol mol(-1) CO2 and in air enriched with CO2 to a concentration of approxi mately 700 mu mol mol(-1). No unambiguous effects of the methanol appl ications were detected in net photosynthesis measurements made on foli age in either of the two CO2 treatments. The 75% increase in CO2 howev er, raised the upper-limiting leaf temperature for positive net photos ynthesis by approximately 7 C, which resulted in a 75% enhancement in net photosynthesis at a leaf temperature of 31 C, a 100% enhancement a t a leaf temperature of 35 C, and a 200% enhancement at 42 C.