Influence of tree species on glomalin-related soil protein and organic carbon fractions in reclaimed post-coal-mining sites

The choice of tree species for restoring postmining landscapes critically determines soil development, yet its specific effects on the dynamics of soil organic carbon (SOC), soil nitrogen, and glomalin-related soil protein (GRSP) fractions remain inadequately quantified. We investigated the influence of five tree species (Scots pine, black alder, black locust, pedunculate oak, and European larch) on the distribution of carbon and nitrogen among three physical SOC fractions—free light fraction (FLF), occluded light fraction (OLF), and mineral-associated fraction (MAF)—and on GRSP concentrations in a reclaimed post-coal-mining site. The trees investigated were 24–28-year-old stands, and soil samples were collected at depths of 0–10 cm and 10–30 cm. Our findings demonstrate that the choice of tree species significantly altered the pathways of SOC and nitrogen accumulation and stabilization. Recalcitrant litter under Scots pine promoted slow-cycling carbon, sequestered primarily in the FLF pool, whereas nitrogen-fixing species (black alder and black locust) and pedunculate oak enhanced the accumulation of stable carbon and nitrogen in physically protected (OLF) and mineral-associated (MAF) fractions. GRSP concentration was the highest under black alder, with average values of 6.52 mg g⁻ 1 at 0–10 cm and 4.43 mg g⁻ 1 at 10–30 cm. Moreover, GRSP fractions were strongly positively correlated with OLF carbon and MAF nitrogen fractions, indicating that GRSP plays a pivotal mechanistic role in the formation of stable aggregates and organo-mineral complexes during pedogenesis. These results highlight how different tree species influence the dynamics of labile and stable soil organic matter pools differently. Our findings suggest that nitrogen-fixing broadleaf species (black alder and black locust) and the ectomycorrhizal species pedunculate oak should be prioritized during postmining land restoration to optimize GRSP enrichment and the sequestration of stable SOC and nitrogen.