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Plant and Soil

, Volume 321, Issue 1–2, pp 5–33 | Cite as

Carbon flow in the rhizosphere: carbon trading at the soil–root interface

  • D. L. Jones
  • C. Nguyen
  • R. D. Finlay
Review Article

Abstract

The loss of organic and inorganic carbon from roots into soil underpins nearly all the major changes that occur in the rhizosphere. In this review we explore the mechanistic basis of organic carbon and nitrogen flow in the rhizosphere. It is clear that C and N flow in the rhizosphere is extremely complex, being highly plant and environment dependent and varying both spatially and temporally along the root. Consequently, the amount and type of rhizodeposits (e.g. exudates, border cells, mucilage) remains highly context specific. This has severely limited our capacity to quantify and model the amount of rhizodeposition in ecosystem processes such as C sequestration and nutrient acquisition. It is now evident that C and N flow at the soil–root interface is bidirectional with C and N being lost from roots and taken up from the soil simultaneously. Here we present four alternative hypotheses to explain why high and low molecular weight organic compounds are actively cycled in the rhizosphere. These include: (1) indirect, fortuitous root exudate recapture as part of the root’s C and N distribution network, (2) direct re-uptake to enhance the plant’s C efficiency and to reduce rhizosphere microbial growth and pathogen attack, (3) direct uptake to recapture organic nutrients released from soil organic matter, and (4) for inter-root and root–microbial signal exchange. Due to severe flaws in the interpretation of commonly used isotopic labelling techniques, there is still great uncertainty surrounding the importance of these individual fluxes in the rhizosphere. Due to the importance of rhizodeposition in regulating ecosystem functioning, it is critical that future research focuses on resolving the quantitative importance of the different C and N fluxes operating in the rhizosphere and the ways in which these vary spatially and temporally.

Keywords

Carbon cycling Nitrogen cycling Mycorrhizas Organic matter Review Rhizodeposition Root processes Signal transduction 

Notes

Acknowledgements

The authors would like to address special thanks to L. Pagès (INRA, Avignon) for providing simulations from root architecture models.

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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.School of the Environment & Natural ResourcesBangor UniversityBangorUK
  2. 2.INRAUMR1220 TCEMVillenave d’OrnonFrance
  3. 3.Uppsala BioCenter, Department of Forest Mycology and PathologySLUUppsalaSweden

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