Diurnal patterns of chlorophyll fluorescence and CO, fixation in orchard grown Torreya taxifolia (Arn.)132

KO E H N, A.C. (Alabama A&M University, Normal, AL 35762) AND R.L. DOUDRICK (Southern Institute of Forest Genetics, Saucier, MS 39574). Diurnal patterns of chlorophyll fluorescence and CO, fixation in orchard grown Torreya ta.n’jdiu (Am.). Bull. Torrey Bot. Sot. 126:93398. 1999.-Chlorophyll fluorescence and CO, fixation measurements were taken on sunny days in October, 1996, on three Torreyu taxifolia (Am.) plants grown in an open canopy orchard. Information from chlorophyll fluorescence quenching analysis indicated during periods of highest light intensity and temperatures there were reductions in yield of photosystem II photochemistry and photochemical quenching and increases in nonphotochemical quenching. Photochemical quenching and yield of photosystem II recovered by the end of the measurement period in late afternoon to levels measured at the beginning of the day. Nonphotochemical quenching remained at high levels for a longer period of time and by late afternoon had not returned to levels measured at the beginning of the day. Diurnal patterns of CO, fixation and stomata1 conductance showed decreases in the afternoon as ambient temperatures remained high and light intensity began to decrease. Internal CO, partial pressures remained constant throughout most of the day, possibly indicating the presence of nonstomatal limitations to photosynthesis. The measurements of CO, fixation and chlorophyll fluorescence on the three T. tax@lin plants in this study indicate that the plants recovered from daily periods of high light and temperatures suggesting that they may tolerate higher light conditions than found in their native habitat.