Mechanisms of Nutrient Uptake
Prior to absorption, nutrients reach the root by 3
Mass flow – movement with the water flow.
Diffusion – movement in response to a
concentration gradient. Slow.
Root interception – root extension. Very
important to find new nutrient sources.
Absorption through roots
Passive Uptake: Some ions such as nitrate, can move
passively through the outer membrane of the root surface
along with water in the transpiration stream.
Active Uptake: Not well understood, but many nutrients (e.g.,
K+ and H2PO4
-) must somehow bond with an ion-specific
carrier (see Insight: p.270).
Maintaining an Electrical Balance: As cations are absorbed
H+ is excreted or organic anions are produced. As anions are
- is excreted or compensating cations are
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•Rapid absorption of soluble ions from nutrient
•Used mostly for the immediate correction of
critical nutrient deficiencies.
•Most efficient for the micronutrients. Does not
build soil fertility. Danger of phytotoxic effects
if over applied.
Absorption through leaves