Factors Affecting on Response of Broad Bean and Corn to Air Quality and Soil CO_2 Flux Rates in Egypt

摘要

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 × 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 uL CO_2 L~(-1); non-filtered (NF) air; NF + 150 μL 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 CO_2 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 P_s 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.