|
As a part of the environmental air quality assessment studies, we have conducted spectral characterizations of steady state fluorescence and canopy level reflectance measurements in responses to the air quality treatments. These studies have been carried out under well watered and restricted soil moisture regimes. Our primary objective was to evaluate fluorescence technique for the nondestructive assessment of plants grown in elevated CO2, elevated O3, and both elevated CO2 and O3 environments under normal and restricted soil moisture conditions. The experimental field site is located at the South Farm, USDA/BARC, Beltsville, Maryland. We used field open-top chamber systems to simulate four altered combinations of tropospheric CO2 and O3 environments under well watered and restricted soil moisture conditions. The simulated gaseous environments included: (1) charcoal-filtered (CF) ambient air as the control chamber; (2) elevated CO2 consisted of CF ambient air plus 150 plus or minus 10 (mu) l/l CO2; (3) elevated O3 that consisted of Non-Filtered (NF) ambient air and addition of 35 plus or minus 5 nl/l O3; and (4) high CO2 and O3 chamber which consisted of NF ambient and additions of 150 plus or minus 10 (mu) l/l CO2 and 35 plus or minus 5 nl/l O3. The CO2 was supplied for 18 hours (3:00 to 21:00 h EST) per day from a CO2 bulk tank. In the elevated O3 treatment chambers, 35 plus or minus 5 nl/l O3 was supplied during seven hour period from 9:00 to 16:00 h EST per day. Both gases were supplied for the entire growing season from early July to late-October. Two soybean cultivars 'Essex' and 'Forrest' were planted in the OTC. Fluorescence images were acquired at F450, F550, F680, and F740. The results showed that fluorescence responses of 'Essex' and 'Forrest' were significantly different in all four bands. Restricted soil moisture treatment had significant effects in that means for F450 and F550 bands significantly increased in both cultivars. The increases in fluorescence intensities at F450 and F550 for 'Essex' due to restricted soil moisture were much greater than those of 'Forrest.' At F680 and F740 bands, only 'Essex' was significantly affected by soil moisture treatment. The most significant effects of elevated CO2 and O3 were observed at F450 and F550 bands. Means for elevated O3 in ambient air in both cultivars were significantly higher in both soil moisture regimes. However, no significant differences between CF and NF+CO2+O3 within a soil moisture treatment were observed. Means for CF+CO2 was significantly lower for both cultivars under well watered soil condition at F450. In general, none of the treatment means were significantly affected by elevated O3 treatments at F680 and F740. Although visible stress symptoms such as chlorosis, discoloration, or necrosis were not evident in the leaves used in this study, F450 and F550 fluorescence images depicted the effects of elevated O3, partial compensation of elevated O3 effects by the elevated CO2, and positive physiological effects of elevated CO2. Plant stresses that cause localized damage may not be easily detected with small field of view point measurements. Imaging a whole leaf may provide better means to study the effects of non-systemic stresses. We are also currently investigating reflectance techniques for a possible complementary use with fluorescence measurements in the remote assessment of above treatment effects.
|
