Biodiversity of key soil phylotypes is associated with increased plant richness and productivity following agricultural abandonment and afforestation

Abstract Anthropogenic land use modifications are causing severe degradation of terrestrial ecosystems, and multiple revegetation strategies are emerging globally to counteract the loss of plant richness and productivity. While soil microorganisms are essential for plant community dynamics, the role of soil microbial biodiversity in regulating changes in plant richness and productivity under different revegetation strategies remains unknown. We used multitrophic co‐occurrence networks to identify soil network modules of strongly co‐occurring phylotypes along a 50‐year revegetation chronosequence of agricultural abandonment and afforestation. Soil biodiversity within these modules was related to soil nutrient cycling functions, plant richness and productivity (understorey layer in afforestation), elucidating how these network modules are associated with changes in plant richness and productivity. Plant richness and productivity increased simultaneously following both agricultural abandonment and afforestation. However, the biodiversity of key soil taxa within distinct network modules was associated with these coupled increases through the regulation of different nutrient cycling functions. Key soil phylotypes within the network modules involved in nitrogen (N) cycling correlated with the simultaneous increase in plant richness and productivity following agricultural abandonment. In contrast, those involved in phosphorus (P) and sulphur (S) cycling were linked to the coupled responses of both plant richness and productivity under afforestation. This reflects the divergent microbial mechanisms associated with the coupled increase in plant richness and productivity along the revegetation chronosequence for both agricultural abandonment and afforestation. Synthesis. Our findings provide correlative evidence that the biodiversity of key phylotypes within soil network modules is closely associated with the simultaneous increase in plant richness and productivity following the cessation of agricultural management. We identify key soil taxa, specific to each revegetation strategy, that could serve as potential targets for genomic and cultivation‐based approaches to counteract plant community degradation. Revegetation efforts to enhance plant richness and productivity should focus on soil phylotypes associated with N cycling after agricultural abandonment and those involved in P and S cycling during afforestation.