Diurnal patterns of chlorophyll fluorescence and CO2 fixation in orchard grown Torreya taxifolia (Arn.).
Diurnal patterns of chlorophyll fluorescence and CO2 fixation in orchard measurements were taken on sunny days in October 1996, on three Torreya taxifolia (Arn.) plants grown in an open canopy orchard. Information from chlorophyll fluorescence quenching analysis indicated that 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 CO2 fixation and stomatal conductance showed decreases in the afternoon as ambient temperatures remained high and light intensity began to decrease. Internal CO2 partial pressures remained constant throughout most of the day, possibly indicating the presence of nonstomatal limitations to photosynthesis. The measurements of CO2 fixation and chlorophyll fluorescence on the three T. taxifolia 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.