JXB Advance Access published online on October 21, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern246
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Accounting for sap flow from different parts of the root system improves the prediction of xylem ABA concentration in plants grown with heterogeneous soil moisture
1The Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
2Dpto. Producción Vegetal, Universidad Politécnica de Cartagena, E-30203 Cartagena, Spain
* To whom correspondence should be addressed: E-mail: I.Dodd{at}lancaster.ac.uk
When soil moisture is heterogeneous, sap flow from, and ABA status of, different parts of the root system impact on leaf xylem ABA concentration ([X-ABA]leaf). The robustness of a model for predicting [X-ABA]leaf was assessed. ‘Two root-one shoot’ grafted sunflower (Helianthus annuus L.) plants received either deficit irrigation (DI, each root system received the same irrigation volumes) or partial rootzone drying (PRD, only one root system was watered and the other dried the soil). Irrespective of whether relative sap flow was assessed using sap flow sensors in vivo or by pressurization of de-topped roots, each root system contributed similarly to total sap flow during DI, while sap flow from roots in drying soil declined linearly with soil water potential (
soil) during PRD. Although soil of the irrigated pot determined the threshold soil at which sap flow from roots in drying soil decreased, the slope of this decrease was independent of the wet pot soil. Irrespective of whether sap was collected from the wet or dry root system of PRD plants, or a DI plant, root xylem ABA concentration increased as soil declined. The model, which weighted ABA contributions of each root system according to the sap flow from each, almost perfectly explained [X-ABA] immediately above the graft union. That the model overestimated measured [X-ABA]leaf may result from changes in [X-ABA] along the transport pathway or an artefact of collecting xylem sap from detached leaves. The implications of declining sap flow through partially dry roots during PRD for the control of stomatal behaviour and irrigation scheduling are discussed.
Key words: ABA, deficit irrigation, grafting, irrigation scheduling, modelling, partial rootzone drying, sap flow, soil moisture heterogeneity
Received 9 July 2008; Revised 6 September 2008 Accepted 9 September 2008
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