Trace metals complexation behavior with root exudates induced by salinity from a mangrove plant Avicennia marina (Forsk.) Vierh

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 (logK_a) 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 logK_a 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⁺.

Keywords:

• Salinity
• root exudates
• complexation
• trace metals
• EEM spectrometry
• mangrove

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.

Additional information

Funding

This work was financially supported by the National Key Research and Development Program of China [2017YFC0506102] and the Natural Science Foundation of China (NSFC) [31870581, 31570586 and 31501822], the Scholarship Award for Excellent Doctoral Student granted by the Chinese Ministry of Education.