A precise gravimetric method for simulating drought stress in pot experiments

Many different approaches have been used for the simulation of drought stress in pot studies. An ideal technique should (i) maintain uniform soil water content within the rooting zone, (ii) allow the rate at which stress develops to be precisely controlled, regardless of differences in plant size or variations in environmental conditions, (iii) permit a range of physiologically distinct stress levels to be imposed and maintained indefinitely, and (iv) provide a means of accurately quantifying the stress level. In the present study, a computer automated null-balance lysimeter was evaluated against these criteria. Separate experiments were conducted with soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) growing in 2.5-L pots. Single plant water use was quantified gravimetrically by frequent, automated recording of pot weights, and transpired water was replaced by a computer controlled watering system such that relative soil water content (RSWC) was maintained within a narrow range. In this way, pots were held at four RSWC levels ranging from 20 to 75%. Despite the frequent additions of small amounts of water at the tops of the pots, soil water distribution within the pots was found to be remarkably uniform, suggesting that bulk RSWC was a suitable indicator of the soil water deficit experienced by the roots. Measurements of whole plant water use indicated that the four RSWC levels represented four statistically distinct levels of water stress. It is concluded that null balance lysimetry is a useful approach to simulating drought stress in greenhouse experiments, with specific advantages over other available techniques.