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 and 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). pp. 278-287.

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Abstract

Oxygen (O-2) supply and the related redox potential (E-H) are important parameters for interactions between roots and microorganisms in the rhizosphere. Rhizosphere extension in terms of the spatial distribution of O-2 concentration and E-H is poorly documented under aerobic soil conditions. We investigated how far O-2 consumption of roots and microorganisms in the rhizosphere is replenished by O-2 diffusion as a function of water/air-filled porosity. Oxygen concentration and E-H in the rhizosphere were monitored at a mm-scale by means of electroreductive Clark-type sensors and miniaturized E-H electrodes under various matric potential ranges. Respiratory activity of roots and microorganisms was calculated from O-2 profiles and diffusion coefficients. pH profiles were determined in thin soil layers sliced near the root surface. Gradients of O-2 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 O-2 transport in the rhizosphere. Under water-saturated conditions and near field capacity up to -200 hPa, O-2 transport was limited, causing a decline in oxygen partial pressures (pO(2)) 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 O-2 increased considerably. This was confirmed by E-H around 300 mV under aerated conditions, while E-H decreased to 100 mV on the root surface under near water-saturated conditions. Gradients of pO(2) and pH from the root surface indicated an extent of the rhizosphere effect of 10-20 mm. In contrast, E-H gradients were observed from 0 to 2 mm from the root surface. We conclude that the rhizosphere extent differs for various parameters (pH, Eh, pO(2)) and is strongly dependent on soil moisture.

Document Type: Article
Additional Information: Times Cited: 0
Research affiliation: Kiel University
OceanRep > The Future Ocean - Cluster of Excellence
ISSN: 1436-8730
Projects: Future Ocean
Date Deposited: 18 Oct 2016 03:47
Last Modified: 24 Sep 2019 00:03
URI: http://oceanrep.geomar.de/id/eprint/32727

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