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| Titel |
Mucilage: The hydraulic bridge between roots and soil |
| VerfasserIn |
Andrea Carminati, Mohsen Zarabanadkouki, Eva Kroener, Mutez A. A. Ahmed |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088245
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| Publikation (Nr.) |
 EGU/EGU2014-2332.pdf |
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| Zusammenfassung |
| As plant roots take up water and the soil dries, water depletion is expected to occur in
the soil near the roots, the so called rhizosphere. Ultimately, as the soil hydraulic
conductivity drops and the soil cannot sustain the transpiration demand, roots shrink and
lose contact to the soil. Both, water depletion in the rhizosphere and formation of
air-filled gaps at the root-soil interface potentially limit the availability of water to
plants. How can plants overcome these potential hydraulic barriers at the root-soil
interface?
One strategy consists in the exudation of mucilage from the root tips. Mucilage is a polymeric
gel that is capable of holding large volumes of water. When exuded into the soil, mucilage
remains in the vicinity of roots thanks to its relatively high viscosity and reduced surface
tension. As mucilage is mainly made of water, its slow penetration into the soil results in
higher water content and hydraulic conductivity of the rhizosphere compared to
the adjacent bulk soil. Recent measurements with a root pressure probe technique
demonstrated that mucilage exudation facilitates the water flow in dry soils. Additionally,
mucilage increases the adhesion of soil particles to the roots, reducing the formation of
gaps at the root-soil interface. Based on these observations, it is very tempting to
conclude that mucilage acts as an optimal hydraulic bridge across the root-soil
interface.
However, as mucilage dries and ages, it turns hydrophobic. Consequently, the rhizosphere
becomes water repellent and its rewetting time increases. Our former experiments showed
that after irrigation subsequent to a drying cycle, the rhizosphere of lupines remained
markedly dry for 2 days. Recently, we demonstrated that the rhizosphere water
repellency is concomitant with a decrease in local water uptake of 4-8 times. We
conclude that after drying and rewetting, the rhzisophere temporarily limits root water
uptake.
In summary, the hydraulic properties of the root-soil interface changes over time and along
the root system. Young, well hydrated mucilage optimally connects the roots to the soil and
facilitates the uptake of water from relatively dry soils. However, as mucilage ages and dries,
it reduces the rhizosphere wettability and the water flow to the roots. Such a dual behavior of
the rhizosphere, rather than a contradiction, seems a plant strategy to adapt to the typically
heterogeneous distribution of water in soils. For instance, in a soil profile with water
stored in the sub soil, mucilage would facilitate the water uptake of young, deep root
segments and it would avoid water loss from the root segments into the dry top
soil.
These studies show that the root-soil interactions in the rhizosphere play a crucial
role in regulating root water uptake. We believe that s better understanding and
management of such interactions can bring a more efficient and sustainable use of water
resources. |
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