Glomalin-related soil protein produced by arbuscular mycorrhizal fungi: its role in Pb stabilization at heavily contaminated sites.

Glomalin-related soil protein (GRSP), produced by arbuscular mycorrhizal fungi (AMF), plays a key role in stabilizing potentially toxic elements. This study evaluated the impact of Pb contamination on GRSP content in rhizosphere soil and its contribution to Pb binding at heavily contaminated sites. AMF colonization, spore density, and AMF species richness and diversity were also assessed. Additionally, methodological tests were conducted to evaluate the suitability of protocols for quantifying the amount of Pb bound to GRSP. Soil and root samples were collected from three dominant plant species at 20 locations near an abandoned Pb smelter, along with three uncontaminated locations. A Pb concentration gradient (149.28-77,588.77 mg kg) was identified. GRSP, classified into easily extractable (EE-GRSP: 0.46-1.75 mg g) and total (T-GRSP: 1.22-3.89 mg g), was detected at all sites. GRSP content was not directly affected by Pb contamination, but showed a positive association with AMF richness and diversity. The abundance of the morphospecies Acaulospora rehmii, A. scrobiculata, Entrophospora infrequens, Funneliformis geosporus, and Racocetra fulgida correlated positively with T-GRSP. Reliable quantification of Pb bound to GRSP required protein precipitation followed by dialysis. Pb bound to T-GRSP (2.03-548.54 mg g) increased with soil Pb, while the percentage of soil Pb retained by GRSP decreased (23.13-1.04 %). Nevertheless, the same amount of T-GRSP bound 77 times more Pb in the most contaminated location compared to the least. Therefore, enhancing the GRSP pool, particularly through AMF morphospecies related to higher GRSP content, may be a key strategy for AMF-assisted phytoremediation.