Effect of calcium and magnesium on the growth and calcite encrustation of Chara fibrosa

• Chara fibrosa was exposed to calcium (Ca), magnesium (Mg), and their combination.
• Observed the effect of Ca and Mg on growth and calcite encrustation of C. fibrosa.
• Calcite encrustation was positively correlated with Ca in water.
• Shoot elongation and chlorophyll content of plants were reduced due to Ca exposure.
• The presence of Mg in water inhibited the calcite encrustation of C. fibrosa.

Chara fibrosa was grown hydroponically using three treatment concentrations (4, 40, and 80 ppm) of calcium (Ca), magnesium (Mg), and their combination (Ca + Mg) for 6 weeks in order to determine the effect of Ca and Mg on its growth and calcite encrustation. Calcite encrustation was positively correlated with the concentration of Ca in the water; however, when plants were grown in water containing high concentrations of Ca, shoot elongation was retarded and chlorophyll content was relatively low. The presence of Mg in the water inhibited calcite encrustation in C. fibrosa and magnesite was not deposited on plants, even in those plants that received Mg without Ca. Further, a high concentration of Ca in the water significantly decreased the Fv/Fm value of C. fibrosa. The presence of Mg in the media slightly decreased the stress caused by the excessive presence of Ca. Encrustations were observed in the intercellular space of plants, and point analysis performed using electron microscopy indicated that these encrustations were composed of calcite. Line analysis and element mapping confirmed that the encrustations contained only Ca with most of the Mg distributed in the cells of C. fibrosa.