Diurnal patterns of chlorophyll fluorescence and CO2 fixation in orchard grown Torreya taxifolia (Arn.)

Chlorophyll fluorescence and CO2 fixation measurements were taken on sunny days in October, 1996, on three Torreya taxifolia (Am.) plants grown in an open canopy orchard. Information from chlorophyll fluorescence quenching an alysis indicated during periods of highest light intensity and temperatures there were reductions in yield of photosystem II photochemistry and photoc hemical quenching and increases in nonphotochemical quenching. Photochemica l quenching and yield of photosystem II recovered by the end of the measure ment period in late afternoon to levels measured at the beginning of the da y. Nonphotochemical quenching remained at high levels for a longer period o f time and by late afternoon had not returned to levels measured at the beg inning of the day. Diurnal patterns of CO2 fixation and stomatal conductanc e showed decreases in the afternoon as ambient temperatures remained high a nd light intensity began to decrease. Internal CO2 partial pressures remain ed constant throughout most of the day, possibly indicating the presence of nonstomatal limitations to photosynthesis. The measurements of CO2 fixatio n and chlorophyll fluorescence on the three T. taxifolia plants in this stu dy 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.