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| Titel |
Mucilage exudation facilitates root water uptake in dry soils |
| VerfasserIn |
Mutez Ahmed, Eva Kroener, Maire Holz, Mohsen Zarebanadkouki, Andrea Carminati |
| 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 |
250088817
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| Publikation (Nr.) |
 EGU/EGU2014-2978.pdf |
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| Zusammenfassung |
| As plant roots take up water and the soil dries, water depletion is expected to occur in the
rhizosphere. However, recent experiments showed that the rhizosphere of lupines was wetter
than the bulk soil during root water uptake. On the other hand, after irrigation the rhizosphere
remained markedly dry and it rewetted only after one-two days. We hypothesize that: 1)
drying/wetting rates of the rhizosphere are controlled by mucilage exuded by roots; 2)
mucilage alters the soil hydraulic conductivity: in particular, wet mucilage increases the soil
hydraulic conductivity and dry mucilage makes the soil water repellent; 3) mucilage
exudation favors root water uptake in dry soil; and 4) dry mucilage limits water loss from
roots to dry soils.
We used a root pressure probe to measure the hydraulic conductance of artificial roots sitting
in soils. As an artificial root we employed a suction cup with a diameter of 2 mm and a length
of 45 mm. The root pressure probe gave the hydraulic conductance of the soil-root
continuum during pulse experiments in which water was injected into or sucked
from the soil. First, we performed experiments with roots in a relatively dry soil
with a volumetric water content of 0.03. Then, we repeated the experiment with
artificial roots covered with mucilage and then placed into the soil. As a model for
mucilage, we collected mucilage from Chia seeds. The water contents (including that of
mucilage) in the experiments with and without mucilage were equal. The pressure
curves were fitted with a model of root water that includes rhizosphere dynamics.
We found that the artificial roots covered with wet mucilage took up water more
easily.
In a second experimental set-up we measured the outflow of water from the artificial roots
into dry soils. We compared two soils: 1) a sandy soil and 2) the same soil wetted with
mucilage from Chia seeds and then let dry. The latter soil became water repellent. Due to the
water repellency, the outflow of water from the root in this soil was significantly
reduced.
The experiments demonstrated that mucilage increased the hydraulic conductance of the
root-soil continuum and facilitated the extraction of water from dry soils. The increase in
conductivity resulted from the higher water content of the soil near the roots. Mucilage has a
lower surface tension than pure water and a higher viscosity, resulting in a slower
penetration of mucilage into the soil. After mucilage was placed into the soil, it
did not spread into the bulk soil, but it remained near the roots, maintaining the
rhizosphere wetter and more conductive than the bulk soil. However, as mucilage
dried, it turned water repellent and reduced the back flow of water from the root to
soil.
We hypothesize that mucilage exudation is a plant strategy to locally and temporally facilitate
water uptake from dry soils. After drying, mucilage becomes water repellent and
may limit the local uptake of water after irrigation. On the other hand, mucilage
water repellency may as well be a strategy to reduce water loss from roots to dry
soils. |
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