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

Abstract

AbstractOzone (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.