Factors affecting on response of broad bean and corn to air quality and soil CO(2) flux rates in Egypt

In response to worldwide increases in the burning of fossil fuels to meet energy demands for electric power generation and transportation, atmospheric CO(2) concentrations are currently rising at approximately 0.5\% per year and ground-level O(3) values are increasing at a rate of 0.32\% per year. Some plants showed positive increases in response to elevated atmospheric CO(2) concentrations, but are depressed when exposed to enhanced O(3) air pollution. The objective of this research was to examine relationships between alterations in leaf plant characteristics in response to air quality treatments and soil CO(2) flux activities during the growing season. Field studies were conducted in 2-m diameter x 2-m height open-top chambers (OTC's) at Sharkia Province during 2004 and 2005 involving the growth of broad bean (Vicia faba L. cv. Giza 40) and corn (Zea mays L. cv. 30 K8) in rotations using no-till management while being subjected full-season to five air quality treatments: charcoal-filtered (CF) air; CF + 150 mu L CO2 L(-1); non-filtered (NF) air; NF + 150 mu L CO(2) L(-1) and ambient air (AA). Leaf photosynthesis (P(s)), leaf area index (LAI), and vegetative carbohydrate contents were determined during pre- and post-anthesis in the two crops and soil CO2 flux rates were monitored monthly during two growing seasons (2004-2005). Multiple and stepwise regression analyses were performed to establish linkages between plant canopy characteristics and soil CO(2) flux rates with results combined over growth stages and year for each crop. Increasing the atmospheric CO(2) concentration typically stimulated leaf P(s), soluble and total leaf carbohydrate contents, LAI values, and soil CO(2) flux rates throughout the growing season in both crop; however, the elevated O(3) treatments in NF air tended to lower these values compared to CF air. Soil CO(2) flux rates were significantly correlated with LAI, soluble and total sugar contents at P <= 0.01 and with Ps rates at P <= 0.05 in broad bean leaves, but with soluble and total sugar contents of leaves in corns at P <= 0.01 only. Results of this study provided solid evidences linking the impact of changing air quality on plants factors processes and possible indirect effects on soil CO(2) flux activities throughout the growing season.