Forest development induces soil aggregate formation and stabilization: Implications for sequestration of soil carbon and nitrogen

Soil aggregates contribute to the accumulation of soil organic carbon and nitrogen, which is critical for the maintenance of multiple forest ecosystem services. However, little is known regarding the direction and magnitude of changes in soil aggregates as forests develop, along with their consequences for carbon and nitrogen sequestration. For this study, we investigated the formation of soil aggregates and their influences on soil organic carbon and total nitrogen stocks in a 6-45 y chronosequence (6, 15, 20, 25, 30, 35, 41, and 45 y) of Metasequoia glyptostroboides plantations. We found that mean weight diameter and geometric mean diameter, as well as the proportion of soil macroaggregates (Ø > 0.25 mm) increased with stand age, suggesting increases in the stability of soil aggregates as forest develops. Furthermore, stand development induced an accumulation of soil aggregate-associated organic carbon and total nitrogen. Plant fine root biomass, soil exchangeable Ca2+ and Mg2+, and soil amorphous Fe-oxides also increased with stand age, which helped to explain the size distribution and stability of soil aggregates. Our results demonstrate that stand development provides robust aggregate protection for soil organic carbon and nitrogen, which better elucidates how both abiotic and biotic binders affect soil aggregate stability. These findings will guide the establishment and management of tree plantations, thereby contributing to developing a stable soil carbon pool and mitigating global climate change.