Applying 'drought' to potted plants by maintaining suboptimal soil moisture improves plant water relations.

Jaime Puértolas,Ian C Dodd,William J Davies,Elisabeth K Larsen

doi:10.1093/jxb/erx116

Abstract

Pot-based phenotyping of drought response sometimes maintains suboptimal soil water content by applying high-frequency deficit irrigation (HFDI). We examined the effect of this treatment on water and abscisic acid (ABA) relations of two species (Helianthus annuus and Populus nigra). Suboptimal soil water content was maintained by frequent irrigation, and compared with the effects of withholding water and with adequate irrigation. At the same average whole-pot soil moisture, frequent irrigation resulted in larger soil water content gradients, lower root and xylem ABA concentrations ([X-ABA]), along with higher transpiration rates or stomatal conductance, compared with plants from which water was withheld. [X-ABA] was not uniquely related to transpiration rate or stomatal conductance, as frequently irrigated plants showed partial stomatal closure compared with well-watered controls, without differing in [X-ABA] and, in H. annuus, [ABA]leaf. In two P. nigra genotypes differing in leaf area, the ratio between leaf area and root weight in the upper soil layer influenced the soil water content of this layer. Maintaining suboptimal soil water content alters water relations, which might become dependent on root distribution and leaf area, which influences soil water content gradients. Thus genotypic variation in 'drought tolerance' derived from phenotyping platforms must be carefully interpreted.

Highlights

The study of plant responses to drought is becoming even more relevant under the current uncertainties regarding food and energy security under a changing climatic scenario
At the same average whole-pot soil moisture, frequent irrigation resulted in larger soil water content gradients, lower root and xylem abscisic acid (ABA) concentrations ([X-ABA]), along with higher transpiration rates or stomatal conductance, compared with plants from which water was withheld. [X-ABA] was not uniquely related to transpiration rate or stomatal conductance, as frequently irrigated plants showed partial stomatal closure compared with well-watered controls, without differing in [X-ABA] and, in H. annuus, [ABA]leaf
Whole-pot soil water content was 50% lower in distribution within this treatment (D/RW) and highfrequency deficit irrigation (HFDI) compared with watering with 100% (WW), but values were similar in D/RW and HFDI at any time of the day, as intended (Fig. 2A). gs was higher at midday than in the morning (Fig. 2B)

Summary

Introduction

The study of plant responses to drought is becoming even more relevant under the current uncertainties regarding food and energy security under a changing climatic scenario. The use of automated systems favours the use of frequent or continuous weighing of pots, with frequent irrigation aiming to restore a pre-determined pot weight corresponding to a specific soil moisture target, over sustained periods of time (Granier et al, 2006; Pereyra-Irujo et al, 2012; Tisne et al, 2013). This method was discussed and defined by Blum (2011) as being of questionable physiological relevance in phenotyping genotypic variation in drought resistance

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Conclusion