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Effects of Ozone and Water Deficit on Field-Grown Soybean: II. Leaflet Nonstructural Carbohydrates

USDA-ARS, Dep. of Crop Science, 1509 Varsity Dr., Raleigh, NC 27606;

Steven F. Vozzo

North Carolina Dep. Environment, Health, & Natural Resources, 3800 Barrett Dr., Raleigh, NC 27609;

Robert P. Patterson

Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7620;

Walter A. Pursley

Dep. of Crop Science, 1509 Varsity Dr., Raleigh, NC 27606;

Allen S. Heagle

USDA-ARS, Dep. of Plant Pathology, 1509 Varsity Dr., Raleigh, NC 27606.

^* Corresponding author (jmiller{at}asrr.arsusda.gov).

ABSTRACT

Ozone (O₃) and water deficit can suppress photosynthesis, growth, and yield of crops, and both may alter plant carbohydrate status. Little is known, however, concerning the combined effects of these stresses on C assimilation and nonstructural carbohydrate reserves in field-grown plants. Soybean [Glycine max (L.) Merr. ‘Young’] plants were subjected to two soil moisture regimes (providing well-watered and periodically water-deficient conditions) and three levels of O₃ in open-top field chambers throughout the growing season. The O₃ concentrations were 0.018, 0.059, and 0.085 µL L^–1 (seasonal mean 12 h d^–1 concentration). Leaflet carbohydrate concentrations were measured periodically during the growing season. Total soluble carbohydrates (TSCs) (sucrose and hexose) and starch were measured in the center leaflet of the sixth trifoliolate from the apex. Ozone stress suppressed leaflet concentrations of TSCs and starch on most sampling dates. Impacts of water deficit were less consistent, but starch concentrations usually increased when effects were significant. Interactions between the two stresses occurred infrequently, although water stress reduced the negative effects of O₃ on sucrose and TSCs when the data were analyzed over the season. Ozone treatment also slightly increased the proportion of sucrose compared to starch in the total nonstructural carbohydrate (TNC) pool. The response of seasonal mean TNC concentrations, seasonal mean NCER, and seed yield to O₃ followed similar patterns, although TNCs were suppressed more on a relative basis than NCER or yield.

Cooperative investigations of the USDA-ARS and the North Carolina State University. Research partly supported by an Interagency Agreement (No. DW-12931347-7601) between the Environmental Protection Agency and the USDA.

Although the research described in this article was partly funded by the USEPA, it has not been subjected to the EPA's paper and policy review and may not reflect the views of the Agency.

Received for publication May 3, 1994.