Transpiration response of Arabidopsis, maize, and soybean to drying of artificial and mineral soil

Water-deficit stress is a major constraint on plant productivity and consequently, is a major focus of much research. Stress is often imposed on plants in these experiments by withholding water from the artificial potting media on which the plants are grown. No attention has been given, however, to the possibility of differences in the dynamics of stress imposition between that resulting from dehydration of the artificial rooting media and that of drying of mineral soil. The objective of this research was to compare transpiration rates during drying of a mineral soil and of an artificial potting mixture for three test species: Arabidopsis thaliana, maize (Zea mays), and soybean (Glycine max). These results showed major differences in transpiration response between the two soil media. Drying of mineral soil confirmed previous observations that no decrease in transpiration rates occurred until 0.27–0.34 of the extractable water remained in the soil. Thereafter, there was essentially a linear decrease in transpiration with further soil drying. In contrast, transpiration rates of plants grown on the potting mixture began to decrease when about 0.6–0.7 of the extractable water still remained in the soil. Consequently, plants grown on the potting mixture as compared to the mineral soil were exposed to stress very early in the drying cycle and the stress was much more prolonged over a wide range of soil moistures. Caution is warranted in extrapolating to natural, mineral soils the results obtained from plants subjected to water-deficits using artificial potting mixtures.