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Oxygen and redox potential gradients in the rhizosphere of alfalfa grown on a loamy soil


Uteau, Daniel; Hafner, Silke; Pagenkemper, Sebastian Kouso; Peth, Stephan; Wiesenberg, Guido L B; Kuzyakov, Yakov; Horn, Rainer (2015). Oxygen and redox potential gradients in the rhizosphere of alfalfa grown on a loamy soil. Journal of Plant Nutrition and Soil Science, 178(2):278-287.

Abstract

Oxygen (O₂) supply and the related redox potential (Eʜ) are important parameters for interactions between roots and microorganisms in the rhizosphere. Rhizosphere extension in terms of the spatial distribution of O₂ concentration and Eʜ is poorly documented under aerobic soil conditions. We investigated how far O₂ consumption of roots and microorganisms in the rhizosphere is replenished by O₂ diffusion as a function of water/air-filled porosity. Oxygen concentration and Eʜ in the rhizosphere were monitored at a mm-scale by means of electroreductive Clark-type sensors and miniaturized Eʜ electrodes under various matric potential ranges. Respiratory activity of roots and microorganisms was calculated from O₂ profiles and diffusion coefficients. pH profiles were determined in thin soil layers sliced near the root surface.
Gradients of O₂ concentration and the extent of anoxic zones depended on the respiratory activity near the root surface. Matric potential, reflecting air-filled porosity, was found to be the most important factor affecting O₂ transport in the rhizosphere. Under water-saturated conditions and near field capacity up to –200 hPa, O₂ transport was limited, causing a decline in oxygen partial pressures (pO₂) to values between 0 and 3 kPa at the root surface. Aerobic respiration increased by a factor of 100 when comparing the saturated with the driest status. At an air-filled porosity of 9% to 12%, diffusion of O₂ increased considerably. This was confirmed by Eʜ around 300 mV under aerated conditions, while Eʜ decreased to 100 mV on the root surface under near water-saturated conditions. Gradients of pO₂ and pH from the root surface indicated an extent of the rhizosphere effect of 10–20 mm. In contrast, Eʜ gradients were observed from 0 to 2 mm from the root surface. We conclude that the rhizosphere extent differs for various parameters (pH, Eh, pO₂) and is strongly dependent on soil moisture.

Abstract

Oxygen (O₂) supply and the related redox potential (Eʜ) are important parameters for interactions between roots and microorganisms in the rhizosphere. Rhizosphere extension in terms of the spatial distribution of O₂ concentration and Eʜ is poorly documented under aerobic soil conditions. We investigated how far O₂ consumption of roots and microorganisms in the rhizosphere is replenished by O₂ diffusion as a function of water/air-filled porosity. Oxygen concentration and Eʜ in the rhizosphere were monitored at a mm-scale by means of electroreductive Clark-type sensors and miniaturized Eʜ electrodes under various matric potential ranges. Respiratory activity of roots and microorganisms was calculated from O₂ profiles and diffusion coefficients. pH profiles were determined in thin soil layers sliced near the root surface.
Gradients of O₂ concentration and the extent of anoxic zones depended on the respiratory activity near the root surface. Matric potential, reflecting air-filled porosity, was found to be the most important factor affecting O₂ transport in the rhizosphere. Under water-saturated conditions and near field capacity up to –200 hPa, O₂ transport was limited, causing a decline in oxygen partial pressures (pO₂) to values between 0 and 3 kPa at the root surface. Aerobic respiration increased by a factor of 100 when comparing the saturated with the driest status. At an air-filled porosity of 9% to 12%, diffusion of O₂ increased considerably. This was confirmed by Eʜ around 300 mV under aerated conditions, while Eʜ decreased to 100 mV on the root surface under near water-saturated conditions. Gradients of pO₂ and pH from the root surface indicated an extent of the rhizosphere effect of 10–20 mm. In contrast, Eʜ gradients were observed from 0 to 2 mm from the root surface. We conclude that the rhizosphere extent differs for various parameters (pH, Eh, pO₂) and is strongly dependent on soil moisture.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Uncontrolled Keywords:soil aeration; oxygen diffusion; air-filled porosity; rhizosphere; hotspots
Language:English
Date:2015
Deposited On:17 Nov 2015 13:30
Last Modified:08 Dec 2017 14:59
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:1436-8730
Publisher DOI:https://doi.org/10.1002/jpln.201300624

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