Hydraulic conductivity of the root-soil interface of lupin in sandy soil after drying and rewetting - Plant and Soil

Aims

The putative role of the rhizosphere in controlling root water uptake is receiving increasing attention. Recent experiments showed that the rhizosphere turned temporarily hydrophobic after drying and subsequent rewetting. Our objective was to investigate whether the rhizosphere hydrophobicity influences the hydraulic conductivity of the rhizosphere-root continuum.

Methods

Lupins were grown in aluminium containers filled with a sandy soil. When the plants were 30 days-old, the soil was let dry to a water content of 2–4 % and then it was irrigated. The soil water content during irrigation was imaged using a time-series neutron radiography. By image processing, we quantified the increase in the volume of water in the roots upon irrigation. Using this information and additional measurements of the root pressure after irrigation, we calculated the water flow into the roots and the total hydraulic conductance of the rhizosphere-root continuum, K _tot .

Results

The radiographs showed that: 1) the rhizosphere stayed temporarily dry after irrigation; 2) as the rhizosphere slowly rewetted, the roots rehydrated of 63 %. During 2 to 3 h subsequent to irrigation, K _tot increased from 1.36 ± 1.09 × 10⁻¹¹ m² s⁻¹ MPa⁻¹ to 5.02 ± 2.13 × 10⁻¹⁰ m² s⁻¹ MPa⁻¹, approaching the conductance of lupin roots in wet soils measured in previous experiments. Based on our calculations, these values of K _tot correspond to a rhizosphere conductivity of 3.87 ± 1.91 × 10⁻¹⁴ m s⁻¹ (shortly after irrigation) and 1.09 ± 1.64 × 10⁻¹² m s⁻¹ (2–3 h after irrigation).

Conclusions

We conclude that during a drying/wetting cycle, the conductivity of the root-soil interface is a temporary limit to root water uptake. We postulate that the temporary reduced hydraulic conductivity is primarily caused by the rhizosphere water repellency.

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Mutez Ahmed was funded by the German Academic Exchange Service (DAAD). The measurements were conducted at the ICON facility of the Paul Scherrer Institute (PSI), Switzerland. We thank Anders Kaestner, David Mennes and Jan Hovind for their precious technical support during the measurements. We also thank Nele Richter-Harder for helpful suggestions and comments on a previous version of this article.

Compliance with ethical standards

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Conflict of interest

The authors declare that they have no conflict of interest.

Authors and Affiliations

1. Division of Soil Hydrology, Georg-August University of Goettingen, Buesgenweg 2, 37077, Goettingen, Germany

   Mohsen Zarebanadkouki, Mutez A. Ahmed & Andrea Carminati

2. Department of Agricultural Engineering, Faculty of Agriculture, University of Khartoum, Khartoum North, 13314, Shambat, Sudan

   Mutez A. Ahmed

Corresponding author

Correspondence to Mohsen Zarebanadkouki.

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