Rhizodeposition under drought is controlled by root growth rate and rhizosphere water content
Rhizodeposition is an important energy source for soil microorganisms. It is therefore crucial to estimate the distribution of root derived carbon (C) in soil and how it changes with soil water content.
We tested how drought affects exudate distribution in the rhizosphere by coupling 14CO2 labelling of plants and phosphor imaging to estimate C allocation in roots. Rhizosphere water content was visualized by neutron radiography. A numerical model was employed to predict the exudate release and its spatiotemporal distribution along and around growing roots.
Dry and wet plants allocated similar amounts of 14C into roots but root elongation decreased by 48% in dry soil leading to reduced longitudinal rhizosphere extension. Rhizosphere water content was identical (31%) independent of drought, presumably because of the high water retention by mucilage. The model predicted that the increase in rhizosphere water content will enhance diffusion of exudates especially in dry soil and increase their microbial decomposition.
Root growth and rhizosphere water content play an important role in C release by roots and in shaping the profiles of root exudates in the rhizosphere. The release of mucilage may be a plant strategy to maintain fast diffusion of exudates and high microbial activity even under water limitation.
KeywordsRoot exudates Rhizosphere extension Mucilage Convection–diffusion model 14C imaging Neutron radiography
We acknowledge the DFG for funding (Projects CA 921/3-1 and KU 1184/33-1) and ev. Studienwerk Villigst for funding the position of MH.
- Carminati A, Kroener E, Ahmed MA, et al (2016) Water for carbon, Carbon for Water, Vadose Zo J. https://doi.org/10.2136/vzj2015.04.0060
- Farrar J, Hawes M, Jones D, Lindow S (2003) How roots control the flux of carbon to the rhizosphere. Ecology 84:827–837. https://doi.org/10.1890/0012-9658(2003)084[0827:HRCTFO]2.0.CO;2 CrossRefGoogle Scholar
- Holz M, Zarebanadkouki M, Kuzyakov Y et al (2017) Root hairs increase rhizosphere extension and carbon input to soil. Ann Bot. https://doi.org/10.1093/aob/mcx127
- McCully ME, Boyer JS (1997) The expansion of maize root-cap mucilage during hydration. 3. Changes in water potential and water content. Physiol Plant 99(1):169–177Google Scholar
- Soille P (2003) Morphological image analysis: principles and applications. Spiringer Verlag, BerlinGoogle Scholar
- Zarebanadkouki M, Kim YX, Moradi AB et al (2012) Quantification and modeling of local root water uptake using neutron radiography and deuterated water. Vadose Zone J. https://doi.org/10.2136/vzj2011.0196