Various chemical and physical forces in the rhizosphere and a range of plant properties
influence
ion uptake by the root system:
- The chemical nature of the nutrient
and its concentration in the soil solution (particularly
outside the root zone).
- The location of the nutrient relative
to the root.
- The mobility of the element (mass
flow and diffusion), which can lead to the formation of
concentration gradients in the rhizosphere.
Root growth, distribution, and morphology, as well as the physiological ability to
mobilize and
absorb nutrients. Root exudation of:
- Organic, low-molecular-weight compounds
(e.g., amino acids),
- Gelatinous, high-molecular-weight
material (mucilage),
- And sloughed-off cells and tissues
can make mineral nutrients available in different ways:
- Directly, e.g., through chelation,
or
- Indirectly by providing energy for
microbial activity.
Physical aspects of root-soil contact:
- Root hairs develop in the moist air
of large pores and channels (e.g., earthworm burrows, old
root channels).
- There is always a water film on root
and root hair surfaces, connecting them to the soil as a
continuum.
- Roots secrete a layer of mucilage,
typically about 1 µm thick (up to 5 µm), which bridges small
gaps.
- Root biomass formation and distribution
are highly pH- dependent.
- Root-soil contact can be lost due
to soil drying or frost.
- Root-soil contact changes with increasing
root diameter (in dicots, due to cambial growth) or,
in monocots, with decreasing diameter with age.
