Loss of plant functional group mediates microbial community assembly in litter decomposition of alpine fir forest

Global climate warming poses a threat to alpine biodiversity, potentially altering plant functional group composition and diversity in litter mixtures, which may affect decomposition processes. This raises the question: does loss of single plant functional group change the composition and the decomposition capacity of microbial communities? Current research lacks consensus, and the decomposition effects of different microbial taxa remain unpredictable. To address this, we conducted a two-year in situ litter decomposition experiment in alpine fir forest using mesh bags, manipulating leaf litter composition to assess how loss of single plant functional group influences microbial community assembly (fungi and bacteria, abundant and rare taxa). We found that bacterial communities were more sensitive than fungal communities to loss of single plant functional group, with significant changes in the abundance of Alphaproteobacteria. Rare taxa exhibited greater biodiversity shifts than abundant taxa. Litter with higher labile materials content supported greater biodiversity of abundant bacterial community. Our results showed that loss of single plant functional group changes the content of metallic elements (i.e., K and Mn) related to litter degradability, influencing bacterial diversity and driving mixture decomposition. Abundant fungi dominated the microbial decomposition pathway. However, in the later stages of decomposition, litter chemistry and fungal communities converged, resulting in similar mass loss among all litter combinations. In conclusion, abundant fungal communities, particularly stable abundant taxa like Sordariomycetes, play a crucial role in maintaining material cycling stability in alpine ecosystem following loss of plant functional groups during decomposition.