Nematode communities reveal the effect of vegetation cover and grazing on restored coal-mine soils

Nematodes are ubiquitous and widely recognized as bioindicators of soil health across ecosystems. We examined soil-dwelling nematode communities in a reclaimed pasture within a post-mining landscape in Northern Spain, under four treatments combining shrub presence and grazing. Communities were compared with those from the adjacent undisturbed oak forest to evaluate restoration success. Metabarcoding of 50 soil samples (10 per treatment in the mine, and 10 additional from the forest) was performed using a nematode-specific 18S rDNA region and Illumina sequencing. Structural (taxonomic richness, diversity, evenness, dominance and specificity) and functional (trophic guilds) metrics were used to characterize community composition across habitats (forest, mine) and treatments within the mine. We identified 49 families and 98 genera, with higher structural and functional diversity in the forest habitat (e.g., Shannon's diversity ≥2.44 and 1.36, respectively; Pielou's evenness ≥0.70 in all cases). Microbial feeders dominated all habitats and treatments, while omnivorous and predators were well represented in both the forest and mine. Herbivores were frequent in the forest and increased with shrub colonization in the mine. Shrub presence strongly influenced nematode community composition, clearly separating shrub-free mine sites from the others. Grazing had a weaker effect on nematode community structure. These findings underscore the sensitivity of nematode communities to restoration strategies and their value as indicators of soil recovery.