An empirical model predicting xylem sap ABA concentration from root biomass and soil moisture distribution in plants under partial root-zone drying

Puertolas Simon, Jaime and Dodd, Ian Charles and Conesa, Charo (2016) An empirical model predicting xylem sap ABA concentration from root biomass and soil moisture distribution in plants under partial root-zone drying. In: XXIX International Horticultural Congress on Horticulture: Sustaining Lives, Livelihoods and Landscapes (IHC2014): International Symposia on Water, Eco-Efficiency and Transformation of Organic Waste in Horticultural Production. ISHS Acta Horticulturae . ISHS, pp. 147-153. ISBN 9789462611061

Abstract

Partial root-zone drying (PRD) is predicted to increase ABA concentration in the xylem sap ([X-ABA]) without changing leaf water status, thus partially closing the stomata which may enhance plant water use efficiency. Predicting ([X-ABA]) from soil moisture and root distribution data are essential to optimize the application of this technique. Bean (Phaseolus vulgaris) plants were grown in split pots, designed to allow a wide range of root mass distribution to either compartment, and PRD was applied. [X-ABA] was best predicted with an exponential model using the weighted (by root water uptake fraction - RWUF) average of root ABA concentration ([R-ABA]) in each compartment. This confirmed previous results reporting that a model accounting for RWUF is the best predictor of [X-ABA]. RWUF was equal to root mass fraction (RMF) when soil volumetric water content (θv) in the dry compartment was above 0.18 cm3 cm-3, linearly related to RMF when θv<0.18 and RMF>0.7, and null otherwise. [R-ABA] in the dry side had basal values (of 100-150 ng g-1 DW) when θv>0.18 and increased linearly with RMF above that threshold. Therefore, the proportion of roots in dry soil affected [X-ABA] by increasing both root water uptake fraction and ABA accumulation. [R-ABA] in the wet side was also stable when the dry side had θv>0.18 but was linearly related to local θv above that threshold and not to RMF. Simulation modelling showed that irrigating more than 1/3 of the total root mass during PRD had little impact on [X-ABA].