Nutrient Uptake and Organic Acid Anion Metabolism in Lupins and Peas Supplied with Nitrate

Unlike many plants reported in the literature, lupins do not excrete OH− in amounts equivalent to the net excess of inorganic anion uptake over inorganic cation uptake. To investigate the mechanisms involved in the maintenance of charge balance, nutrient uptake and organic anion accumulation of lupins and peas supplied with a range of NO3− concentrations, were compared. Lupins absorbed less NO3− than peas on a dry weight basis, which largely ACCOUNTED for the smaller excess of anion uptake over cation uptake in lupins than in peas at the same NO3− supply. When anion uptake exceeded cation uptake, peas excreted an equivalent charge of OH−, whereas lupins excreted much smaller amounts of OH− than the excess of anion over cation uptake. It was calculated that lupins excreted significant amounts of organic anions when anion uptake exceeded cation uptake, whereas organic anion excretion from peas was negligible, regardless of their NO3− supply and cation–anion balance. In this study, organic anion excretion was measured from lupin roots grown in near-sterile conditions while supplied with NO3− at 0, 500 and 2000 μM. Although complete sterility was not achieved, there was close agreement between the organic anion excreted and the excess anion over cation uptake.