ot excretion of inorganic ions (e.g. HCO3 − , OH− , H+ ) is also important in the mineral nutrition of plants. Plant uptake of anions in excess of cations often causes the roots to secrete HCO3− in order to maintain electrical neutrality, a process that leads to increased rhizosphere pH. Conversely, the uptake of cations in excess of anions can cause roots to exude H+ and lower the rhizosphere pH. The change in pH with HCO3− extrusion tends to increase nutrient sup- ply in acidic soils, as happens with H+ exudation in calcareous soils.