Physiological acidity and alkalinity of inorganic nitrogenous compounds in solution cultures

1. The experimental procedure included complete utilization of the nitrogen in the single salt solutions by the sorghum and maize seedlings used. Simultaneous comparisons were made between parallel solution cultures. Typical comparisons included NH4Cl vs. HCl, NaNO3 vs. NaHCO3, etc. Titrable acidity of the solutions before and after absorption and the pH values of the dried and ground plants after absorption were determined. 2. Parallel cultures of (NH4)2SO4 vs. H2SO4 and of NH4Cl vs. HCl gave residual titrable acidity in each case after the disappearance of the NH4 ions from the cultural solutions. The residual liquids from the ammonium salts showed a greater amount of acidity than did those where the acid was supplied chemically. The pH determinations of the ground material showed that the acids absorbed or physiologically formed within tbe plants were still in evidence. Parallel cultures of NaNO3 vs. NaHCO3 and KNO3 vs. KHCO3 gave residual titrable alkalinity in each case after the disappearance of NO3 ions from the cultural solutions. The residual liquids from the nitrate salts gave smaller amounts of alkalinity in each comparison. The alkalinity absorbed or physiologically formed in each case was clearly shown as still present by the pH determinations of the ground plants. 4. Parallel cultures in solutions of HNO3, NH4NO3, NH4HCO3, and H2O after absorption of all NH4 and NO3 ions gave small amounts of titrable alkalinity in each case. These titration values were practically equal to each other, although the original solutions of HNO3 had marked titrable acidity and those of NH4HCO, marked titrable alkalinity. The pH values determined on the plants from the nitrogen compounds furnished in this group were practically equal to those on the plants grown in water. This showed that the acidity and alkalinity absorbed by plants in this group had largely disappeared in the transformations following absorption. These findings are in accord with theories previously proposed. 5. The plants must use energy in forming proteins from NH4 and NO3 compounds. The amounts of energy required to secure OH ions to go with the NH4 ions and of H ions to go with NO3 ions seem to bear a qualitative relationship to the rates of NH4 and NO3 ion absorption from solutions of different pH values.