Accelerated soil carbon accumulation in an afforested multispecies forest compared with a monoculture driven by...

While afforestation enhances soil organic carbon (SOC) sequestration, how soil nutrients (especially phosphorus, P) correlate with SOC components of distinct biotic origins and mineral associations in tropical afforestation remains unclear. Soil microbial properties link soil nutrient availability and forest type via afforestation. Therefore, to optimize tropical afforestation management, microbial mediation of soil nutrient availability to regulate SOC accumulation needs to be explored. We examined soils along a tropical restoration chronosequence, including a bare land, a Eucalyptus exserta monoculture, an afforested multispecies forest, and a natural forest to assess how SOC responds to afforestation. After 60 years, SOC increased by 68.2 % in the multispecies forest versus 36.5 % in the monoculture. The multispecies forest exhibited greater P availability, indicated by higher available P concentrations and a lower monoester-to-diester phosphate ratio, alongside more labile SOC chemistry. Afforestation increased SOC components with biotic origin and mineral association. It enhanced plant-derived carbon (C) contribution while reducing mineral-associated C contribution. Increased microbial P limitation and shifts in community composition likely promoted soil P mobilization, further stimulating SOC accumulation. These results demonstrate that soil P availability and microbial processes are key drivers of SOC accrual under tropical afforestation and underscore the importance of tree diversity in forest restoration. Future tropical forest management is encouraged to adopt a tree mixing strategy and monitor soil P availability to foster an active soil microbial community, thereby driving SOC accumulation through enhanced plant-microbe interactions.