Changes in plant resource inputs lead to rapid alterations in soil dissolved organic matter composition in an old-growth tropical forest

•Molecular characteristics of soil DOM were altered after short DIRT in a tropical forest.•FT-ICR-MS index-based results were largely consistent with UV/fluorescence results.•O/C, DBE, AImod, and %CRAM increased, and %MLBL decreased in litter removal and no-input plots.•Changes in plant inputs altered the soil DOM composition in an old-growth forest. Alterations in plant resource inputs to soil affect soil organic matter (OM) dynamics. However, it remains unclear how to alter soil dissolved OM (DOM) composition. Here, we used UV/fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry to analyze soil DOM’s optical and molecular characteristics after eight months of detritus input and removal in an old-growth tropical forest. Changes in plant inputs significantly altered soil DOM’s optical properties, and the most pronounced changes were observed in the humification index and fluorescent components. In litterfall removal and no-input plots, molecular characteristic values increased greatly, such as O/C, double-bond equivalent, aromaticity index, and proportion of carboxyl-rich alicyclic molecules, while biolabile compounds decreased. The abundance of lignin-like and tannin-like compounds was more than 20 % higher in litter removal plots than in no-input plots. Our findings indicate that changes in plant resource inputs can lead to rapid alterations in soil DOM composition.