Effect of soil pH on growth and cation deposition in the root tip of Zea mays L.

The effects of sandy soil pH on the distribution of growth velocities and o n cation concentrations and deposition rates in root growth zones of Zea ma ys L. seedlings were investigated. The pH values of the rooting medium vari ed between 4.2 and 8.6 in sand culture (70% saturated) without external sup ply of nutrients. At all pH values, densities (in mu moles per g fresh weig ht) of potassium, magnesium, and calcium increased toward the root tip. Low er pH in the medium increased calcium tissue density fivefold and magnesium density 1.7-fold, whereas the density of potassium, the overall elongation rate, and the growth velocity distribution did not show any significant pH dependence. Throughout the growth zone the deposition rates of the divalen t cations, as calculated on the basis of the continuity equation, increased with lower pH. The data are consistent with the hypothesis that the effect s of pH on the cation deposition rates are due to the increase in the dival ent cation concentration of the soil solution at low pH and that the abunda nt uronic acid residues of the young walls of the meristem provide a reserv oir of storage capacity for Ca and Mg under conditions of low nutrient avai lability.