Clay and biochar additions regulate accumulation of microbial residue carbon within soil aggregates after mining disturbance

In this study, bentonite and biochar were incorporated as soil amendments, and amino sugars were employed as biomarkers to investigate the distribution of microbial necromass carbon within different aggregate size fractions of reclaimed soil in a mining area on the Loess Plateau. The objective was to provide theoretical support for soil carbon sequestration in mining-affected regions. The soil was fractionated into three aggregate size classes: >0.25 mm, 0.25–0.053 mm, and <0.053 mm. The contents of organic carbon (OC) and total nitrogen (TN), as well as the C/N ratio, were determined for each aggregate fraction under different treatments. The results indicated that, following amendment application, the increases in OC and TN contents were significantly greater in macroaggregates compared to microaggregates, relative to bulk soil. Additionally, the concentrations of four amino sugars were quantified across the aggregate fractions to assess changes in the content and distribution of microbial necromass carbon after amendment addition. Using glucosamine (GluN) as a biomarker for fungal necromass carbon and muramic acid (MurN) as a biomarker for bacterial necromass carbon, the analysis revealed that fungi were more sensitive to the application of amendments. Fungal necromass carbon was predominantly enriched in macroaggregates, whereas bacterial necromass carbon accumulated to a greater extent in microaggregates. These findings underscore the critical role of fungal necromass carbon within macroaggregates in the recovery of the soil carbon pool in degraded lands.