Plant roots release phospholipid surfactants that modify the physical and chemical properties of soil

Abstract

Summary• Plant root mucilages contain powerful surfactants that will alter the interaction of soil solids with water and ions, and the rates of microbial processes.• The lipid composition of maize, lupin and wheat root mucilages was analysed by thin layer chromatography and gas chromatography-mass spectrometry. A commercially available phosphatidylcholine (lecithin), chemically similar to the phospholipid surfactants identified in the mucilages, was then used to evaluate its effects on selected soil properties.• The lipids found in the mucilages were principally phosphatidylcholines, composed mainly of saturated fatty acids, in contrast to the lipids extracted from root tissues. In soil at low tension, lecithin reduced the water content at any particular tension by as much as 10 and 50% in soil and acid-washed sand, respectively. Lecithin decreased the amount of phosphate adsorption in soil and increased the phosphate concentration in solution by 10%. The surfactant also reduced net rates of ammonium consumption and nitrate production in soil.• These experiments provide the first evidence we are aware of that plant-released surfactants will significantly modify the biophysical environment of the rhizosphere.

Influence of the rhizosphere in a biopurification system on the dissipation of a pesticide mixture

“…A reported mechanism used by rhizosphere microorganisms to take up contaminants by biosurfactant production, which facilitates contaminant degradation, mainly of hydrophobic compounds, and concomitantly increases their availability to plants (Read et al, 2003). In this context, plant species and soil are reportedly jointly responsible for the structure and function of microbial diversity in the rhizosphere (Berg and Smalla, 2009).…”

Do roots mind the gap?

“…We refer to several recent reviews on the specific physical, chemical, biological properties of the rhizosphere (Gregory 2006;Hinsinger et al 2009); to measurements of water content (Young 1995), structure (Whalley et al 2005), wettability (Read et al 2003), and mechanical stability (Czarnes et al 2000) of the rhizosphere compared to bulk soil; to in-situ infiltration in the rhizosphere (Hallet et al 2003); and to recent observations of unexpected water dynamics in the rhizosphere (Carminati et al 2010). These studies show several controversies, for example in whether the rhizosphere has increased or decreased water content and conductivity compared to the bulk soil.…”

Effect of drought and heat stresses on plant growth and yield: a review

“…This effect can be further increased due to a decrease in soil-root hydraulic conductance related to root shrinkage, which severely hampers water flow to roots (Carminati et al, 2009 and Willatt, 1983). Recent observations point to a rhizospheric effect onto the water relations of this soil-root interface, involving mucilages, root exudates and possibly solute accumulation (Carminati and Vetterlein, 2013;McCully et al, 2009;Read et al, 2003;Stirzaker and Passioura 1996), which would modulate soil-root contact and water uptake with variations in dry or moist soil (White and Kirkegaard, 2010).At longer time scales, not only plasticity in water relations but also in root growth will occur during water deficit, with a decrease in root length (reduced growth, increased mortality) in drier parts and an increase in wetter parts (Huang and Eissenstat, 2000;Sekhon et al, 2010). If an increase in root growth can be observed at the onset of water stress, the continuing drought will reduce the overall root growth, resulting from uncoupling between carbon production in leaves and use in root sinks (root apex) (Muller et al, 2011).…”