Land conversion to cropland homogenizes variation in soil biota, gene assemblages, and ecological strategies on local and regional scales.

It is widely considered that conversion of natural landscapes to agriculture results in biotic homogenization. A recent study comparing soil biota of 27 paired natural steppe soil (NS) and agricultural soil (AS) sites across 900 km in north-eastern China found that conversion to agriculture had increased spatial gradients in soil functional genes. Using the same shotgun metagenome samples, and bacterial amplicon data, we instead analyzed total observed variation at the between-site and within-site level. We found that from the perspective of community taxonomic composition, archaeal and fungal community variation was decreased in AS compared to NS at both within- and between-site scales. In contrast, the bacterial and metazoal community was homogenized only at the local scale. Total functional KEGG gene assemblage was homogenized in AS at both the local and regional scale, whereas "Y-A-S" strategies in bacteria were homogenized at the local scale but not the between-site scale. Overall, these results show a clear homogenizing effect of agriculture with respect to multiple aspects of soil taxonomic and functional diversity, though varying by scale. Certain abiotic soil properties showed homogenization in AS at within-site and between-site scales may explain this homogenization, and uniformity of plant cover in croplands likely contribute to the effect. These findings confirm and extend global-scale studies showing homogenization of soil biota in agricultural environments, revealing that effects extend to functional genes and the broad taxonomic spectrum of life-with potential loss of soil ecosystem resilience to environmental change resulting from agriculture.