A Detrimental Interaction of Subsoil Aluminum and Drought Stress on the Leaf Water Status of Soybean

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Abstract
Drought and subsoil Al are major concerns which face soybean [Glycine max (L.) Merr.] producers in the southeastern USA. However, the interaction of these two factors is not clearly understood. This study was designed to characterize the combined effect of these two stress factors on soybean water status. A greenhouse experiment was conducted, with two levels of subsoil Al saturation (6 and 71%), and two levels of drought stress (watered and unwatered). A split plot experimental design with three replications was employed. Soil treatments were applied via a soil layering technique using topsoil of a Goldsboro sandy loam (fine‐loamy, siliceous, thermic, Aquic Paleudult). The top layer in all pots consisted of the unamended topsoil. In the lower layer, highly contrasting Al saturation levels were obtained by amending one half of the pots with Al2(SO4)3. Data were collected during a 14‐d moisture stress treatment imposed at podfilling (R3). Traits measured were leaf water potential, relative water content, transpiration, and diffusive resistance. A detrimental interaction between subsoil Al and drought was observed in all traits measured. Plants grown in the presence of both stress factors had lower levels of leaf relative water content and water potential, and a lower transpiration rate than predicted additively by independent stress factors. In general, subsoil Al had much greater effects on leaf water status in drought‐stressed soybean plants than in the wellwatered plants. These results suggest that hindered root growth in highly Al‐saturated subsoils may have limited the ability of the plant to withstand drought. Soybean producers in regions characterized by drought and subsoil Al should consider the incorporation of Altolerant germplasm into management systems. Field studies including water stress as a variable should be interpreted with regard to this interaction, if soil A1 is present.

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