NITROGEN FIXATION CHARACTERISTICS OF AZOLLA CAROLINIANA UNDER THE INFLUENCE OF HEAVY METAL (CR⁶⁺)

This study investigated the nitrogen fixation activity of the aquatic plant Azolla caroliniana in different nutrient
media (D and W) under the influence of various concentrations of hexavalent chromium (Cr⁶⁺). During the experiments,
biomass production, growth dynamics, and nitrogen fixation activity of Azolla were evaluated using the acetylene
reduction method. The results showed that in chromium-free nutrient media, nitrogen fixation activity gradually increased
over 10–30 days and exhibited a declining trend after day 35. Nitrogen fixation activity in the W-type nutrient medium was
higher compared to the D medium. Although increasing chromium concentrations significantly reduced nitrogen fixation
activity, the process did not completely cease even at high concentrations (3 mg/L). The results indicate that Azolla
caroliniana is a relatively stable biological object in water environments contaminated with heavy metals.