Mixed‐species afforestation enhances soil multifunctionality through microbial reassembly and SOC molecular diversification

Abstract Afforestation is widely promoted as a means to enhance soil‐based ecosystem functions, yet how different planting strategies regulate soil multifunctionality (SMF), including nutrient provision, enzyme activity and microbial metabolism, remains incompletely understood. Existing studies rely heavily on simple microbial diversity metrics and largely overlook soil organic carbon (SOC) molecular diversity, an emerging and under‐appreciated dimension of what controls decomposition and nutrient release in soil. To clarify how afforestation shapes SMF, we employed a ‘space‐for‐time substitution’ approach and examined a tropical restoration chronosequence including bare land, an Eucalyptus exserta monoculture, an afforested mixed‐species forest and an old‐growth natural forest. We quantified SMF using averaging, multivariate and multi‐threshold approaches, assessed microbial compositional and functional diversity using phospholipid fatty acids and GeoChip functional arrays, and characterized SOC molecular diversity through analytical pyrolysis techniques. Afforestation significantly increased SMF, and mixed‐species forest sites had higher SMF values than monoculture. Increases in SMF were associated with shifts in microbial community composition as well as compositional and functional Shannon diversity. SOC molecular diversity emerged as a key mediator linking microbial attributes to SMF, reflecting a mechanism whereby chemically diversified substrates provide multiple soil functions simultaneously. Synthesis and applications . By integrating microbial and SOC molecular perspectives, our study identifies the mechanistic links connecting afforestation, soil microbial biodiversity and multifunctionality. These findings support the promotion of mixed‐species plantings in tropical afforestation and highlight the importance of improving SOC diversity under afforestation to maximize ecosystem multifunctionality. Read the free Plain Language Summary for this article on the journal's blog .