Microbial diversity drives divergent multifunctionality in global afforestation and reforestation ecosystems

Afforestation and reforestation have emerged as optimal nature-based solutions for global climate mitigation, providing critical ecosystem services and biodiversity benefits. However, the long-term impacts of two restoration modes on multiple ecosystem functions (that is, multifunctionality) at a global scale have long been recognized. Here, we compiled data from 1247 reforestation and afforestation sites worldwide, which encompass a forestation history of up to a hundred years, to explore the long-term effects of forest recovery on ecosystem multifunctionality, including plant productivity, soil carbon accumulation, nutrient cycling, decomposition metabolism, and microbial habitats. Our findings reveal that afforested ecosystems consistently exhibit an upward trend in multifunctionality over this hundred-year span, while reforested ecosystems tend to stabilize in multifunctionality after approximately 30 years. A comprehensive analysis of biotic and abiotic factors revealed that bacterial diversity is a primary driver of increased multifunctionality in afforested ecosystems, while fungal diversity plays a critical role in the initial increase and subsequent stabilization of multifunctionality in reforested ecosystems. Additionally, changes in the soil microenvironment, such as increased soil moisture and improved soil compaction, were identified as key regulators of microbial diversity, thereby impacting ecosystem multifunctionality. Overall, our study demonstrates the substantial ecological restoration potential of both reforestation and afforestation but attention should be paid to microbial diversity in future ecological restoration efforts considering the crucial role in enhancing global ecosystem function restoration and sustainability.