Shifts in the fungal community promote soil carbon accumulation in microaggregates during long‐term secondary succession

Abstract Secondary succession has been demonstrated as one of the effective restoration strategies for enhancing soil organic carbon (SOC) sequestration. Soil aggregates play a crucial role in SOC sequestration by providing habitats for microbes and physically protecting SOC. However, microbial transformations of plant and microbial residues in different aggregate fractions during secondary succession and their implications for SOC sequestration remain unclear. In this study, we investigated the dynamics of plant‐ and microbe‐derived carbon and their contribution to SOC accumulation and the soil microbial community at the soil aggregate scale during long‐term secondary succession. We found that SOC content significantly increased by 40.2% along the long‐term secondary succession. Small macroaggregates (250–2000 μm) and microaggregates (<250 μm) retained a higher proportion of SOC compared with other aggregates. The proportion of SOC rose from the early successional stage (25.7%) to the late stage (42.4%) in microaggregates (53–250 μm), but it decreased in the last successional stage in large macroaggregates (>2000 μm), small macroaggregates and silt–clay particles (<53 μm). Additionally, bacterial and fungal necromass carbon within microaggregates increased by 83.3% and 172.5%, respectively, from the early to late successional stage. Although the direct contribution of plant debris to SOC was negligible compared with that of microbial necromass, it played a crucial role in regulating microbial necromass accumulation by altering microbial community traits (e.g. life strategies and fungal guilds) during long‐term secondary succession. As a result, these changes contributed to shifts in SOC throughout succession, with the effects being more pronounced in microaggregates compared with other aggregate types. Our results emphasize that the mechanisms driving SOC accumulation might be different in various soil aggregate fractions and highlight the crucial importance of fungal communities in microaggregate fractions during long‐term secondary succession. Read the free Plain Language Summary for this article on the Journal blog.