Plant species loss reduces rare soil microbes through diversity effects amplified by multitrophic interactions

Abstract Evidence is mounting that plant diversity loss erodes ecosystem function by altering biochemical processes regulated by diverse organisms both above‐ground and below‐ground. However, we know little about how loss of plant diversity influences soil biodiversity, especially whether loss of ecologically rare and/or functionally distinctive plants leads to reduction in rare soil microbes associated with soil multifunctionality. In species‐rich alpine meadow communities on the Tibetan Plateau, we conducted a 12‐year plant species removal experiment to reveal the effects on soil biodiversity of losing many ecologically rare and functionally distinctive forbs versus the loss of the few dominant sedges and several common species. We found that the removal of rare forbs, rather than dominant species and common plants, significantly decreased the richness of soil bacteria and fungi by decreasing rare microbial taxa in later years. This decline in the richness of rare microbial taxa was attributable not only to the decreased plant species richness but also to the increased abundance of fungivorous and omnivorous nematodes. Synthesis . The study revealed that the loss of rare plants induces the loss of rare soil microbes through plant diversity effects amplified by below‐ground multitrophic interactions. Loss of rare soil microbes triggers larger shifts in the microbial community that alter soil biodiversity, food web structure and community functioning.