Ion diameter: The larger the
ion, the slower its uptake (e.g., potassium is taken up faster than
cesium).
Valency: Valency influences
how strongly an ion binds to a reaction site (protein, phospholipid).
Binding strength increases with valency: uncharged molecules < cation⁺ < cation²⁺
< cation³⁺ (a
similar principle applies to anions).
pH: pH alters the predominant
ionic form in which a given element can exist (e.g., HPO₄²⁻
<=>H2PO4⁻ ; NH3 <=> N4⁺).
Metabolic activity: Energy
is produced through respiration (the reversal of photosynthesis). Lower
oxygen supply reduces nutrient uptake; low carbohydrate (CHO) availability reduces nutrient
uptake.
Temperature: Higher temperatures
increase metabolic activity (Q10 effect). Low temperatures
reduce membrane fluidity, root and shoot growth, and consequently, nutrient demand.
External ion concentration: Uptake
is generally regulated by a feedback mechanism. High
external concentrations can lead to luxury consumption.
