An efficient method for the collection of root mucilage from different plant species—A case study on the effect of mucilage on soil water repellency Ina-Maria Zickenrott 1,2 , Susanne K. Woche 3 , Jo ¨ rg Bachmann 3 , Mutez A. Ahmed 4,5 , and Doris Vetterlein 1,2 * 1 Department of Soil Physics, Helmholtz Centre for Environmental Research – UFZ, Theodor-Lieser-Str. 4, 06120 Halle/Saale, Germany 2 Soil Science, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle/Saale, Germany 3 Institute of Soil Science, Leibnitz University Hannover, Herrenha ¨user Str. 2, 30419 Hannover, Germany 4 Division of Soil Hydrology, Georg-August University of Go ¨ ttingen, Go ¨ ttingen 37077, Germany 5 Department of Agricultural Engineering, Faculty of Agriculture, University of Khartoum, Khartoum North, 13314, Shambat, Sudan Abstract Root mucilage may play a prominent role in understanding root water uptake and, thus, there is revived interest in studying the function of root mucilage. However, mucilage research is ham- pered by the tedious procedures of mucilage collection. We developed a mucilage separator which utilizes low centrifugal forces (570 rpm) to separate the mucilage from seminal roots with- out the need of handling individual seeds or removing the germinated seeds from the tray/mesh to a centrifuge tube. For the different plant species, between 1 and 3.7 mL tray –1 of hydrated mu- cilage could be produced, with 6 trays being handled successively within 45 min. For Triticum aestivum, which showed a dry matter content of 0.5%, this was equivalent to 98.6 mg mucilage dry matter. The lowest total production was found for Zea mays with just 34 mg dry matter. The amounts of mucilage produced normalized to root tip agree well with literature data. The mucilage obtained by the new method was used to measure its effect on repellency of soil as this property directly relates to the phenomenon of lower rhizosphere soil water content during rewetting. It could be shown that repellency of the rhizosphere is affected by the quantity as well as by species-dependent quality of mucilage in the rhizosphere. Among the species tested (Lupinus albus, Vicia faba, Zea mays, Triticum aestivum), the largest differences were observed between the two legumes. For Zea mays seminal root mucilage obtained with the new system was compared to mucilage of air born brace roots. The differences between these two muci- lages, representing different root orders, indicate clearly that there is still a need for methods which enable the investigation of roots from older plants. Key words: mucilage / rhizosphere / contact angle / hydrophobicity / Zea mays / Vicia faba / Lupinus albus / Triticum aestivum Accepted January 20, 2016 1 Introduction Rhizosphere soil hydraulic properties have been shown by re- cent research to differ from those of the bulk soil (Carminati and Vetterlein, 2013). This throws into question a central as- sumption made by Gardner (1960) for his microscopic model on soil water uptake by plant roots. Most microscopic ap- proaches investigating root water uptake use Gardner ’s (1960) model, so there is a major need for research to explore factors driving the unique hydrological properties of rhizo- sphere soil. It has been hypothesized that the changes ob- served are related to the presence of mucilage. The effect of mucilage, which has a high water holding capacity, is a delay of decrease in rhizosphere soil water content during drying. As a result, rhizosphere hydraulic conductivity declines less rapid, which enables extension of water depletion zone around roots. During rewetting, hydrophobicity is observed and both effects depend on root age (Carminati, 2013). Kro- ener et al. (2014) have developed an approach for modelling the non-equilibrium water dynamics based on the presence of mucilage and successfully reproduced experimental data with this model. However, there is still a lack of experimental evi- dence for root mucilage being the key for understanding root water uptake. This has revived the interest in studying the function of root mucilage (Carminati and Vetterlein, 2013; Ahmed et al., 2014; Kroener et al., 2015). Research on function of root mucilage has been constrained by the methodological problems of obtaining root mucilage. For chemical analysis root tips of seeds germinated in humid air have been suspended in sterile distilled water for a certain time (Chaboud, 1983; Moody et al., 1988; Knee et al., 2001; Timotiwu and Sakurai, 2002). The water containing the muci- lage is then processed further. For collection of hydrated mu- cilage as gel the standard procedure is to collect mucilage with a pipette from the root tip of seeds germinated in humid air under sterile or non-sterile conditions (Guinel and McCully , 1986; Read et al., 1999). This procedure is very tedious and ª 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 294 10.1002/jpln.201500511 J. Plant Nutr. Soil Sci. 2016, 179, 294–302 * Correspondence: Dr. D. Vetterlein; e-mail: doris.vetterlein@ufz.de