Afforestation alters functions of soil and microbiome but does not drive soil carbon accumulation in two decades

Afforestation has been proposed as an effective strategy for restoration and carbon sequestration, however, its impacts on the functions of soils and microbiome remain poorly understood. By analyzing 144 afforestation sites across a 159 000 square kilometer watershed in China, a typical region characterized with rapid forest expansion in global land-use change map, we provided the first large-scale observation evidence that afforestation did not drive net accumulation of soil carbon and nitrogen in two decades. Afforestation significantly shifted the soil microbial community and their functional profiles of element cycling, increased soil prokaryotic diversity but reduced fungal diversity. Afforestation reduced the network complexity of soil prokaryotes but did not change the complexity of fungal networks. Planting introduced- poplar reduced soil multifunctionality while native trees did not change multifunctionality. Our results reveal the ecological responses of soils to afforestation across a broad geographic scale and provide new insights for forest restoration programs.