| Abstract: | Direct observations of the calcium-45 distribution around the roots of plants growing in soil showed a pattern in direct contrast to that predicted from calculations based on the calcium concentration of the soil solution, transpiration rates, and plant calcium content. Whereas calcium-45 accumulation at the root surface was predicted, depletion was observed. It is suggested that preferential water movement in larger pores may decrease the expected solution calcium accumulation at the root surface. However, autoradiographs may give no indication of soil solution concentration depletion or accumulation because of the relatively high level on the colloid surface. The nature and extent of the depletion indicates how profoundly the plant root alters its immediate environment in the soil. |
