Abstract
SummaryWe hypothesized that plant exudates could either gel or disperse soil depending on their chemical characteristics. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were collected using an aerated hydroponic method and compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analogue. Sandy loam soil was passed through a 500‐μm mesh and treated with each exudate at a concentration of 4.6 mg exudate g−1 dry soil. Two sets of soil samples were prepared. One set of treated soil samples was maintained at 4°C to suppress microbial processes. To characterize the effect of decomposition, the second set of samples was incubated at 16°C for 2 weeks at −30 kPa matric potential. Gas chromatography–mass spectrometry (GC–MS) analysis of the exudates showed that barley had the largest organic acid content and chia the largest content of sugars (polysaccharide‐derived or free), and maize was in between barley and chia. Yield stress of amended soil samples was measured by an oscillatory strain sweep test with a cone plate rheometer. When microbial decomposition was suppressed at 4°C, yield stress increased 20‐fold for chia seed exudate and twofold for maize root exudate compared with the control, whereas for barley root exudate decreased to half. The yield stress after 2 weeks of incubation compared with soil with suppressed microbial decomposition increased by 85% for barley root exudate, but for chia and maize it decreased by 87 and 54%, respectively. Barley root exudation might therefore disperse soil and this could facilitate nutrient release. The maize root and chia seed exudates gelled soil, which could create a more stable soil structure around roots or seeds.Highlights Rheological measurements quantified physical behaviour of plant exudates and effect on soil stabilization.Barley root exudates dispersed soil, which could release nutrients and carbon.Maize root and chia seed exudates had a stabilizing effect on soil.Physical engineering of soil in contact with plant roots depends on the nature and origin of exudates.
Highlights
Soil physical conditions, in the rhizosphere, are continually modified by the release of plant root exudates and microbial metabolites (McCully, 1999; Hinsinger et al., 2009)
The quantity and physicochemical characteristics of root exudates are determined by the plant species, the age of an individual plant and external factors such as biotic and abiotic stresses e.g. soil structure, presence of microorganisms, and nutritional status (Gransee & Wittenmayer, 2000; Jones et al, 2004; Lesuffleur et al, 2007)
The first part of this study examined physicochemical characteristics of barley root, maize root and chia seed exudates
Summary
In the rhizosphere, are continually modified by the release of plant root exudates and microbial metabolites (McCully, 1999; Hinsinger et al., 2009). The effect of biological exudates on soil physical properties might depend on their physicochemical characteristics (Czarnes et al, 2000). The quantity and physicochemical characteristics of root exudates are determined by the plant species, the age of an individual plant and external factors such as biotic and abiotic stresses e.g. soil structure, presence of microorganisms, and nutritional status (Gransee & Wittenmayer, 2000; Jones et al, 2004; Lesuffleur et al, 2007). Sugars (often polysaccharide-derived), amino acids and organic acids are usually released in the largest quantities (Dakora & Philips, 2002; Carvalhais et al, 2011)
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