4.3 ǀ Nutrient uptake antagonisms and effects of accompanying
anions
High concentrations of Fe2+ at the root surface may
suppress uptake of other cations through antagonistic effects (Wu,
Holtkamp, Wairich & Frei, 2019). Plants suffer from ionic imbalance
through competition between similarly charged cations for binding and
carrier sites. In submerged soils, the main anion balancing cations in
solution is generally HCO3- (Section
2). A decrease in the rhizosphere pH as above and consequent decrease in
HCO3- concentration means that any
Fe2+ entering the root will be accompanied by a
proportion of Cl- or
SO42- rather than
HCO3-. If Fe2+enters with HCO3-, acidity generated
in Fe2+ oxidation in the plant will be neutralized by
conversion of HCO3- to
CO2, which is assimilated or lost. Whereas if it enters
with a non-volatile anion, Fe2+ oxidation will produce
the equivalent amount of free H+ in the plant, with
damaging effects on plant tissues (van Mensvoort, Lantin, Brinkman &
Van Breemen, 1985). We know of no studies exploring this effect.
Yamauchi (1989) found the severity of Fe toxicity in rice in Fe toxic
soils supplied with K2SO4 was less than
that with KCl, but he attributed the effect to reduction of sulphate to
sulphide in the soil and precipitation of Fe(II) sulphides, lowering the
concentration of Fe2+ in solution and hence its
uptake.