Intercropping enhances stable soil organic carbon pool through macroaggregate protection and biochemical recalcitrance interactions

Abstract

Diversified cropping can enhance soil organic carbon (SOC); however, the mechanisms through which it alters the SOC pool and microbial regulation remain unclear. This study examined the responses of the stable SOC pool to intercropping and nitrogen (N) fertilization in a seven-year field experiment involving three cropping patterns: maize monoculture, potato monoculture, and maize/potato intercropping, under three N levels. Intercropping increased SOC content by 9.8–36.1 % and the stable C pool (the sum of the slow and resistant SOC pools) by 12.3–72.1 % in bulk soil compared to monocultures, with the maximum increase at the low nitrogen (LN) level. The enhanced stable C pool in intercropping was primarily attributed to greater proportion of large macroaggregates (> 2 mm) and increased aromaticity of SOC within these macroaggregates. Although N fertilization in intercropping did not affect SOC aromaticity, it further increased the proportion of large macroaggregates at the LN level. Intercropping shifted the microbial keystone taxa related to SOC formation from oligotrophic bacteria (e.g., Anaerolineaceae from Chloroflexi) in potato monoculture to copiotrophic bacteria (e.g., Micromonosporaceae of Actinobacteria), accompanied by a higher abundance from Chaetomiaceae of Sordariomycetes among the fungal keystone taxa within macroaggregates. These shifts reflected increased activities of carbon cycling enzymes (e.g., peroxidases and α-/β-glucosidase) and a higher proportion of large macroaggregates, facilitating the formation and accumulation of aromatic C in intercropping. This study provides insights into how intercropping enhances SOC stocks and offers guidance on N fertilization strategies to promote SOC sequestration in diversified cropping systems.