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Response of root respiration and root exudation to alterations in root C supply and demand in wheat

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Abstract

Rising atmospheric CO2 concentrations have highlighted the importance of being able to understand and predict C fluxes in plant-soil systems. We investigated the responses of the two fluxes contributing to below-ground efflux of plant root-dependent CO2, root respiration and rhizomicrobial respiration of root exudates. Wheat (Triticum aestivum L., var. Consort) plants were grown in hydroponics at 20°C, pulse-labelled with 14CO2 and subjected to two regimes of temperature and light (12 h photoperiod or darkness at either 15°C or 25°C), to alter plant C supply and demand. Root respiration was increased by temperature with a Q 10 of 1.6. Root exudation was, in itself, unaltered by temperature, however, it was reduced when C supply to the roots was reduced and demand for C for respiration was increased by elevated temperature. The rate of exudation responded much more rapidly to the restriction of C input than did respiration and was approximately four times more sensitive to the decline in C supply than respiration. Although temporal responses of exudation and respiration were treatment dependent, at the end of the experimental period (2 days) the relative proportion of C lost by the two processes was conserved despite differences in the magnitude of total root C loss. Approximately 77% of total C and 67% of 14C lost from roots was accounted for by root respiration. The ratio of exudate specific activity to CO2 specific activity converged to a common value for all treatments of 2, suggesting that exudates and respired CO2were not composed of C of the same age. The results suggest that the contributions of root and rhizomicrobial respiration to root-dependent below-ground respiration are conserved and highlight the dangers in estimating short-term respiration and exudation only from measurements of labelled C. The differences in responses over time and in the age of C lost may ultimately prove useful in improving estimates of root and rhizomicrobial respiration.

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Acknowledgements

We thank the UK Natural Environment Research Council, the British Council-Germany Academic Exchange Service and the German Research Foundation for funding this investigation. We also thank Gareth Williams, Jonathan Roberts and Jim Frith for technical support.

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Authors and Affiliations

  1. School of Biological Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, Wales, UK

    Paul Hill & John Farrar

  2. Department of Agroecosystem Research, University of Bayreuth, 95440, Bayreuth, Germany

    Yakov Kuzyakov

  3. School of the Environment and Natural Resources, University of Wales, Bangor, Gwynedd, LL57 2UW, Wales, UK

    David Jones

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  1. Paul Hill
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  2. Yakov Kuzyakov
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  3. David Jones
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  4. John Farrar
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Correspondence to Paul Hill.

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Hill, P., Kuzyakov, Y., Jones, D. et al. Response of root respiration and root exudation to alterations in root C supply and demand in wheat. Plant Soil 291, 131–141 (2007). https://doi.org/10.1007/s11104-006-9180-6

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  • DOI: https://doi.org/10.1007/s11104-006-9180-6

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