Abstract
This study investigated the characteristics of exudates from mangrove plant Avicennia marina seedling roots under 0, 200 and 600 mM NaCl treatments and their complexation behavior with trace metals using excitation emission matrix (EEM) fluorescence spectrometry. Two fulvic-like fluorescence peaks, namely peak A (Em = 440 nm, Ex = 250 nm, UV fulvic-like compounds) and peak B (Em = 440 nm, Ex = 340 nm, visible fulvic-like compounds) were identified. The fluorescence intensities of peak A and peak B were enhanced by increasing salinity. Furthermore, the fluorescence of both peaks could be quenched by the ions of copper (Cu2+), manganese (Mn2+) and cadmium (Cd2+). Conditional stability constant (logKa) exhibited that binding capacity of both peak A and peak B with trace metals are Cu2+ > Mn2+ > Cd2+ in the range from 2.21 to 4.01. Besides, Hill coefficient (n) >1 for Cu2+ but n < 1 for Mn2+ and Cd2+. The results of high n and high logKa for Cu2+ rather than Mn2+ and Cd2+ indicate that the fulvic-like compounds in root exudates of A. marina have maximum potential for Cu2+ complexation compared to Mn2+ and Cd2+, suggesting the fulvic acids in root exudates of A. marina have strong complexation with Cu2+ rather than Mn2+ and Cd2+.
Acknowledgments
We pay special thanks to Prof. Chen Xi for technical assistance during the experiments. We are grateful to Kamrul Hasan and Dr. Sajid Masood for editing the article.
Disclosure statement
No potential conflict of interest was reported by the authors.