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.