Afforestation restores the positive soil biodiversity-multifunctionality relationship in tropics and subtropics but not in colder zones

The Earth is currently in an era where massive deforestation and afforestation coexist, however, the consequences of large-scale agricultural deforestation and subsequent afforestation on soil multidiversity, ecosystem multifunctionality (EMF), and their relationships remain unclear. Here, we investigated 405 paired plots along a 4,000 km south-north transect, spanning tropical, subtropical, temperate, and boreal zones. We measured 26 surrogates of ecosystem functions and sequenced soil biomes (including bacteria, fungi, archaea, viruses, protists, and invertebrates) and metagenomes. We find that agricultural deforestation reduces soil multitrophic biodiversity by 37% and EMF by 24%; afforestation has partially restored them, but pristine levels have not been reached. Agricultural deforestation decouples the positive relationships between soil multidiversity and EMF (BEFm) across four climatic zones, while afforestation restores the positive BEFm relationship in tropics and subtropics but not in temperate and boreal zones. Afforestation in the warmer zone triggers multitrophic cascades to enhance EMF, thereby strengthening BEFm relationships. The changes in biogeochemical cycling genes caused by afforestation play more important roles in driving EMF in the warmer zone than the colder zone. This study provides the first evidence that climate modulates the recovery of BEFm relationships and offers novel multitrophic and metagenomic insights into the mechanisms driving EMF.