Combined effects of elevated tropospheric ozone, elevated atmospheric carbon dioxide, and soil moisture deficit on soybean using fluorescence imaging

Increases of atmospheric CO2 and tropospherico O3 as the result of anthropogenic pollution have been observed during the last century and are projected to continue. Frequent occurrences of drought and climate changes are also predicted to occur in association with the global alterations in air quality. The primary objective was to characterize fluorescence responses as a noninvasive detection method for crop species subjected to elevated atmospheric CO2 and O3 under two soil moisture regimes. A laboratory-based fluorescence imaging system (FIS) was developed to capture and process images of plant leaves at the blue (F450), green (F550), red (F680), and far-red (F740) regions of the spectrum. Full surface imaging was superior to point source measurements in assessing fluorescence characteristics of plant leaves.;Field experiments were conducted at the USDA Beltsville Agricultural Research Center during 1997 and 1998 using soybean cultivars 'Essex' and 'Forrest' grown full-season in open-top chambers exposed to four combinations of tropospheric CO2 and O3 under well-watered (WW) vs. restricted moisture (RM) conditions. The gaseous environments included: (1) Charcoal-filtered (CF) ambient air; (2) CF air plus 150 +/- 10 muL L--1 CO2; (3) Non-filtered (NF) ambient air plus 35 +/- 5 nL L--1 O3; and (4) NF air plus 150 +/- 10 muL--1 CO 2 and 35 +/- 5 nL L--1 O3. Soil moisture levels were 0 to --0.05 MPa (WW) vs. --1.0 +/- 0.5 MPa (RM).;The results from this investigation demonstrated that chronic exposures of soybean leaves to air quality treatments varying in O3 and CO 2 concentrations produced significant alterations in steady-state fluorescence values at F450, F550, F680 and F740 even in the absence of visual symptoms or significant changes in gas exchange parameters. Likewise, soil moisture treatments caused significant changes in fluorescence responses throughout the spectrum. The FIS detected the effects of elevated O3, partial compensation of elevated O3 effects in response elevated CO 2, and positive physiological effects of elevated CO2 on plants under WW and RM regimes. Cultivar sensitivities in response to air quality and soil moisture treatments were also differentiated with the FIS. Among the more significant findings in this investigation was that blue-green fluorescence emission from leaves was highly responsive to oxidative O 3 stress at levels that were sub-lethal.;On the basis of findings from this research in conjunction with advances in detector and laser technologies, a laser induced fluorescence imaging system (LIFIS) capable of in situ canopy level measurements was proposed and is currently being developed jointly by NASA/GSFC and USDA/BARC. Future research considerations are addressed for the use of steady-state fluorescence as a viable early remote detection method for assessing plant stress factors.