The multifunctionality of soil aggregates is related to the complexity of aggregate microbial community during afforestation

The multifunctionality of soil ecosystems depends on the soil structure and microenvironment because soil is a multi-structured, interconnected system. However, how the microenvironments of different aggregate affect the soil microbial community and soil multifunctionality remains unknown, which hinders our ability to understand the sustainability of afforestation ecosystems. To address this, we investigated three paired afforestation sequences accosted 629.3 km on the Loess Plateau, China. Our results showed that afforestation significantly increased the stability of soil aggregates and the macroaggregates increased soil multifunctionality, including carbon, nitrogen, and phosphorus cycle functions. In addition, soil enzyme (BG, PO, LAP, and NAG) activities were enhanced by the soil aggregate size, which played a major role in supporting soil multifunctionality. This change was directly affected by soil aggregate size or indirectly affected by the complexity of bacterial co-network and was regulated by carbon restriction and the abundance of core species. In addition, macroaggregate increased the complexity of soil bacterial communities and afforestation enhanced the complexity crossed aggregates with different sizes and consequently affected soil multifunctionality during afforestation. Therefore, the responses of soil microbes in different soil aggregates to afforestation should be considered when assessing the sustainability of afforestation, as different soil structures have varied response to forest ecosystems in semiarid and arid climates.