PARENT SESSION
Posters P1D Photosynthesis and global change. Abstracts (699-710)

Fluorescence as an early indicator of yield suppression by ozone. Edwin Fiscus^{*,1, 2}, Michael Flowers¹, Kent Burkey^{1, 2}, Fitzgerald Booker^{1, 2}, ¹ Air Quality Research Unit, Raleigh, NC, U.S.A.² Crop Science Department, Raleigh, NC, U.S.A.

ABSTRACT- Tropospheric ozone levels over much of the worlds agricultural areas are rising and predicted to continue to increase. Past research has shown that chronic exposure to high ozone concentrations has detrimental effects on crop growth and yield. Early detection of ozone induced changes may increase our understanding of the ozone effect on photosynthesis, crop growth and yield. Our objective was to determine the effects of chronic ozone exposure on the gas exchange, fluorescence parameters and yield of an ozone sensitive line of snapbean (Phaseolus vulgaris L.). In particular, we wanted to determine if gas exchange and/or fluorescence measurements would be able to detect changes due to ozone exposure early enough to serve as a predictor of eventual yield. A replicated experiment was conducted in 2003 and 2004 at Raleigh, NC. Snapbeans were grown in naturally lit environmentally controlled chambers with day/night temperatures of 28C/23C and relative humidities of 50% and 67%. Ozone treatments consisted of 12 hour average ozone concentrations of 0, 15, 30, and 60 ppb. Gas exchange and fluorescence measurements were taken weekly and biweekly respectively until harvest. A small amount of ozone (15 ppb) significantly increased yield 21% compared to the 0 ppb ozone treatment. High ozone concentrations (60 ppb) significantly reduced snapbean yield 87% and 84% compared to the 15 and 0 ppb treatments. During the growing season both the gas exchange and fluorescence parameters were strongly related to yield. However, the earliest relationships with yield were detected with the fluorescence quantum yield and photochemical quenching, as well as the rate of electron transport through PSII that requires a combination of gas exchange and fluorescence measurements. These data suggest that the measurement of electron transport through PSII using fluorescence techniques may be useful as an early indicator of ozone induced damage and predictor of eventual yield.

KEY WORDS: fluorescence, Ozone damage, gas exchange, yield predictor