Precipitation of Calcium and Strontium Sulfates around Plant Roots and its Evaluation
1975
Malzer, G. L. | Barber, S. A.
The flux of Ca²⁺, Sr²⁺, and SO₄²⁻ to corn (Zea mays L.) roots was investigated to determine if accumulation at the root caused precipitates to form and if so to determine the influence of precipitate formation on Ca and Sr uptake. Autoradiographic techniques using ⁴⁵Ca and ³⁵S showed both Ca²⁺ and SO₄²⁻ accumulated at root surfaces when supply by mass-flow exceeded uptake. Petrographic studies of the roots confirmed the formation of CaSO₄ precipitates. The influence of the root precipitate on the relative Ca and Sr uptake was studied by comparing uptake by plants grown where precipitates occurred with those grown without precipitate formation. The corn plants were grown in solution culture. In order to have CaSO₄ precipitation without SrSO₄ precipitation a Ca/Sr molar ratio of 3670 was used. When SrSO₄ precipitation without CaSO₄ precipitation was desired the molar ratio was 0.45. The Ca and Sr in solution were labeled with ⁴⁵Ca and ⁸⁵Sr either from 9 days to harvest or for only 7 hours before harvest. Harvests were made after 13, 17, and 24 days. Plant age at sampling did not affect the ⁴⁵Ca/⁸⁵Sr ratio absorbed, however the length of the labeling period did. When labeled for 7-hours, and CaSO₄ precipitate was present ⁴⁵Ca uptake was reduced 16 to 20% relative to ⁸⁵Sr uptake as compared to uptake where no precipitate was present. When labeled from day 9, no differences occurred. When SrSO₄ precipitated, ⁸⁵Sr translocation was reduced 10 to 20% compared to ⁴⁵Ca with the long labeling treatment. With a Ca/Sr ratio of 3670, the roots selectively accumulated Sr, however with a Ca/Sr ratio of 0.45, the roots selectively accumulated Ca. The Ca/Sr ratio present in the root was not correlated with the Ca/Sr ratio translocated to the shoot.
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