Surface tension, rheology and hydrophobicity of rhizodeposits and seed mucilage influence soil water retention and hysteresis

Naveed, Muhammad, Ahmed, M. A., Benard, P., Brown, L. K., George, T. S., Bengough, A. G., Roose, T., Koebernick, N. and Hallett, P. D. (2019) Surface tension, rheology and hydrophobicity of rhizodeposits and seed mucilage influence soil water retention and hysteresis. Plant and Soil, 437 (1-2). pp. 65-81. ISSN 0032-079X

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Abstract

Abstract
Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and mucilages on hydraulic properties of soils depend on their physicochemical characteristics and origin.
Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and mucilages at 0.46 and 4.6 mg g−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential.
Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and mucilages on soil water retention almost ceased when approaching the wilting point at −1500 kPa matric potential.
Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.

Item Type: Article
Additional Information: This work was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) project ‘Rhizosphere by Design’ (BB/L026058/1, BB/J000868/1 and BB/ J011460/1) with support from a Royal Society University Research Fellowship, EPSRC EP/M020355/1, BBSRC SARIC BB/ P004180/1, NERC NE/L00237/1 and ERC Consolidator grant DIMR 646809. The James Hutton Institute receives funding from the Scottish Government.
Uncontrolled Keywords: Root exudate; Seed exudate; Surface tension; Viscosity; Contact angle; Soil water retention; Hysteresis
Subjects: Construction and engineering > Civil and environmental engineering
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Depositing User: Muhammad Naveed
Date Deposited: 06 Feb 2019 14:16
Last Modified: 23 Apr 2019 11:39
URI: http://repository.uwl.ac.uk/id/eprint/5787

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