Abstract
As a natural organic compound secreted by arbuscular mycorrhizal fungi (AMF), glomalin-related soil protein (GRSP) is an important part in soil, affecting the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in it. Previous research have demonstrated that GRSP could enhance the availability of PAHs in the soil and favor their accumulation in plant roots. However, a scarcity of research exists on the different molecular weights of GRSP interacting with PAHs due to their complexation and heterogeneity. In this research, the extracted GRSP in soil was divided into three molecular weight (Mw) fractions of GRSP (<3,000, 3,000–10,000, and >10,000 Da), whose characteristics and binding capacity of PAHs were conducted by using UV–visible absorption, quenching fluorometry and, Fourier transform infrared spectroscopy. The results showed that the GRSP was composed of abundant compounds, it has a wide distribution of molecular weight, and the >10,000 Da Mw fraction was dominant. For three Mw fractions of GRSP, they have some difference in spectral features, for example, the >10,000 Da fraction showed higher dissolved organic carbon (DOC) contents, more phenolic hydroxyl groups, and stronger UV adsorption capacity than the low and middle Mw fractions. In addition, the interaction between GRSP and phenanthrene is related to the characteristics of the Mw fractions, especially the phenolic hydroxyl group, which has a significantly positive correlation with a binding coefficient of KA (k = 0.992, p < 0.01). Simultaneously, hydrophobic, NH-π, and H-bound also played roles in the complexation of phenanthrene with GRSP. These findings suggested that different GRSPMw fractions could influence the fate, availability, and toxicity of PAHs in soil by their interaction.
Highlights
The terrigenous organic matter plays a vital role in controlling the ibogeochemical processes of contaminants, such as heavy metals and organic contaminants (Wang et al, 2020)
We explored the relationship between different molecular weight (Mw) fractions of glomalin-related soil protein (GRSP) and phenanthrene to illustrate the underlying roles and mechanisms of GRSP on polycyclic aromatic hydrocarbons (PAHs)
From Fourier transform infrared (FTIR) spectra, we found that the absorption intensity of infrared absorptions was weakened and narrower at 3,700–3,400 cm−1 (-OH stretching), 1,700–1,600 cm−1, and 1,500–1,300 cm−1 when phenanthrene was loaded with GRSP (Figure 4)
Summary
The terrigenous organic matter plays a vital role in controlling the ibogeochemical processes of contaminants, such as heavy metals and organic contaminants (Wang et al, 2020). As a secretion of arbuscular mycorrhizal fungi (AMF) in soil, the enormous amount of GRSP in the soil is desirable to quantify AMF potential for carbon sequestration and to improve water-stable aggregates in soil and influence soil fertility (Wright and Upadhyaya, 1996, 1998; Borie et al, 2006; Nichols and Wright, 2006), and so it may remedy soil contamination by complexing with potentially toxic elements, such as heavy metal or organic pollutants in soil (Wang et al, 2020; Tian et al, 2021). Gao et al (2017) found that EE-GRSP and T-GRSP could influence the sorption processes of organic pollutants, like PAHs, in soil and enhance the accumulation of PAHs in roots (Chen et al, 2018). There is a scarcity of reports on the different molecular weights of GRSP, which may have different functional groups
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