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+.

中文翻译：

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红树林植物 Avicennia marina (Forsk.) Vierh 的盐分诱导根系分泌物与痕量金属络合行为

摘要 本研究利用激发发射矩阵 (EEM) 荧光光谱法研究了 0、200 和 600 mM NaCl 处理下红树植物 Avicennia marina 幼苗根系分泌物的特征及其与痕量金属的络合行为。鉴定了两个类富里酸荧光峰，即峰 A（Em = 440 nm，Ex = 250 nm，UV 类富里酸化合物）和峰 B（Em = 440 nm，Ex = 340 nm，可见的类富里酸化合物）。峰A和峰B的荧光强度随着盐度的增加而增强。此外，两个峰的荧光都可以被铜 (Cu2+)、锰 (Mn2+) 和镉 (Cd2+) 离子淬灭。条件稳定性常数 (logKa) 表明峰 A 和峰 B 与痕量金属的结合能力为 Cu2+ > Mn2+ > Cd2+，范围为 2.21 至 4.01。此外，Cu2+ 的 Hill 系数 (n) >1，但 Mn2+ 和 Cd2+ 的 n < 1。Cu2+ 的高 n 和 logKa 值高于 Mn2+ 和 Cd2+ 的结果表明，与 Mn2+ 和 Cd2+ 相比，A. marina 根系分泌物中的富里酸类化合物具有最大的 Cu2+ 络合潜力，表明 A. marina 根系分泌物中的富里酸. marina 与 Cu2+ 而不是 Mn2+ 和 Cd2+ 有很强的络合。