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Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of –OH and –COOH groups with the metal. The –COOH and –OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of –COOH groups followed by –OH groups. The presence of the Ni–C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr–C and Cd–C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration. [Display omitted] • Spectral data combined with molecular docking reveal adsorption mechanism of GRSP. • Metal is mainly immobilized on the GRSP surface through –OH and –COOH groups. • Preferential adsorption on GRSP for metal in sequential order of –COOH > –OH group. • ASP151 and ASP472 residues in GRSP provide coordination sites for metal adsorption. • Ni with smaller hydrated ionic radii forms organometallic complexes with GRSP. [ABSTRACT FROM AUTHOR]

Mangroves are known for sequestering and storing large quantities of phosphorus (P) within their sediments. In the present study, the sediment P cycle (including phosphatase activity intensity, total sedimentary P, P fractions distinguished by a sequential extraction method, as well as diffusion-adsorption processes) in a mangrove swamp in a subtropical estuary in China was studied. In the spring, the acid phosphatase activity varied between 1.3 and 1.9 units in the four sites in the estuary. The activity of alkaline phosphatase varied from 0.8 to 1.4 units. The total sedimentary P ranged from 821 to 1689 mg kg −1 with a dominance of redox-sensitive (Fe/Al bound) P. In the autumn, activities of both phosphatases and the total sediment P amount increased, probably due to enhanced inputs of organic matter and Fe oxides. In addition to seasonal variation, P in the mangrove sediment was influenced by anthropogenic activities. In particular, redox-sensitive P decreased significantly while phosphatase activity increased in the site that was flushed with aquaculture pond effluents. In contrast, sediment P enrichment was observed in the site that received domestic sewage. Both sources of anthropogenic P increased the eutrophication risk of the mangrove sediment because of a decrease in the amount of P adsorption and an enhancement of P release via diffusion. Diesel contamination due to the presence of a dock depressed phosphatase activity in the surficial sediment. The overlap between seasonal rhythm and human influences may introduce significant variations in P cycling, which warrants further attention from coastal management. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) can be transported from mangrove wetlands to the ocean, as a key link in the global carbon cycle. The continuum between mangrove creeks and the ocean is a prime location for facilitating reactions between DOM and sunlight or microbes. Yet, little is known about the sources, transformation, and fate of DOM in the transport continuum at the critical land-to-sea zone. Here, water samples were collected in the estuary of southeastern China along mangrove creeks. We found that DOC concentrations ranged from 6.65 to 110.48 mg/L along the creek-to-estuary continuum. The high accumulation of DOC can be due to the high residence time of seawater and more sensitivity to environmental disturbance. 1.75 times higher DOC concentrations were showed in the lower area than the upper area of the transporting continuum. DOM materials in mangrove creeks were characterized by mostly labile, highly degradable proteins. Terrestrial index (TI) and marine-derived index (MI) were respectively used to described allochthonous and autochthonous characteristics of DOM. The DOM showed a high TI and low MI in the upper area and low TI and high MI in the lower area of outputting continuum. DOM quality along the mangrove to estuary continuum corresponded with environmental heterogeneity. Biodegradation and photo-biodegradation experiments were conducted on DOM samples over 20-days. A rapid 40–65% decrease was observed in DOC concentration in response to biodegradation. About 45% decrease of DOC concentration in photodegradation, afterward less loss in photo-biodegradation than was examined with biodegradation alone. Chromophoric dissolved organic matter (CDOM) concentrations of the continuum were in fluctuating changes during biodegradation. CDOM was preferentially removed 60–90% then increased significantly in photo-biodegradation. Photo-mediated protein-like substances were demonstrated in strong reactions during biodegradation. Compared to biodegradation alone, DOM quality can be distinctly altered during photo-biodegradation. This study demonstrates that DOM quality was gradually homogenized due to interaction with sunlight and microbes during transport from the mangrove creek to the ocean. [Display omitted] • DOC concentrations range in the threshold regulated by sunlight and microbes. • Photo-altered or highly bioavailable CDOM can be pooled from mangroves to estuary. • DOC, CDOM and FDOM were degraded in similar rules yet distinct levels. • Photo-biodegradation altered DOM much more effectively than biodegradation. • DOM quality was homogenized by sunlight and microbes from mangroves to estuary. [ABSTRACT FROM AUTHOR]

• Application of biochar remarkably increased PAH sorption from sediment. • Biochar amendments reduced the PAHs bioavailability in plant tissue after 56 days. • The tested biochars promoted the removal effeciency of PAHs in anaerobic conditions. • Biochar and K. obovata could be a sound remediation treatment when used in combination. [ABSTRACT FROM AUTHOR]