Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/1999
Publication Date: N/A
Citation: Interpretive Summary: Steady increases in worldwide carbon dioxide (CO2) levels and localized increases in ozone (O3) are causing concerns about future crop productivity. Increases in CO2 concentrations have generally increased crop growth and yields, while chronic exposure to high ozone has caused leaf injury and has generally reduced crop growth and yields. Crop responses to these gases have been studied individually. The main objective of this study was to evaluate the combined effects of soil moisture, CO2, and ozone on the grain quality of soybeans. Two cultivars of soybeans were grown in large open top chambers with two soil moisture levels and four air quality treatments (ambient and elevated CO2 and O3). Leaf area index, biomass, and grain yield were reduced by the addition of ozone. Elevated CO2 compensated for the reductions in yields caused by high ozone. High ozone increased protein content, but reduced total oil content of the grain. Total saturated fatty acids were slightly increased by high ozone. Total unsaturated fatty acids were unchanged by air quality or moisture treatments. Soybean tolerance to ozone from a biomass or yield standpoint is not a reliable predictor of ozone tolerance in terms of grain quality. These results indicate that the impact of high ozone on soybean grain quality will be minimal.
Technical Abstract: The effects of enhanced CO2 or O3 on crops have been studied extensively; however, soybean grain quality responses to these combined gases have not been characterized. Field studies were conducted in 1994-1997 to investigate the effects of soil moisture, CO2, and O3 on two soybean (Glycine max (L.) Merr.) cultivars. The two cultivars tested were Essex, an O3-tolerant cultivar, and Forrest, an O3-sensitive cultivar. Plants were grown in three meter diameter open-top chambers (OTCs) at USDA facilities in Beltsville, MD. Two soil moisture regimes were applied, i.e., well watered (WW) and restricted moisture (RM), with four air quality treatments under each regime, i.e., charcoal-filtered (CF) air, CF air with addition of approximately 150 uL CO2 L-1 (CF+CO2), non-filtered (NF) air with addition of 35 + or - 5 nL O3 L-1 (NF+O3), and NF air with addition of both CO2 and O3 (NF+CO2+O3). High O3 generally increased protein contents with a trend to reduce total oil contents. Total saturated fatty acid contents were increased under high O3 under WW conditions. Total unsaturated fatty acids were not significantly affected by air quality treatments or moisture regime. Sensitivity of seed quality to high O3 under reduced moisture availability varies with cultivar. Soybean tolerance to O3 from a biomass or yield standpoint may not be a valid predictor of O3 tolerance in terms of grain quality. Further research appears warranted to establish relationships among cultivars to combined stresses involving moisture and O3 air quality.