Shift of microbial taxa and metabolisms relying on carbon sources of rhizodeposits and straw of Zea mays L

Decoding the fundamental taxa that decompose crop rhizodeposits (rhizo-C) and/or straw residue (straw-C) is crucial for understanding the role of plant-derived carbon (C) in driving microbial community assembly and consequent C decomposition. Here, a parallel ¹³C-labeling design, DNA-SIP, and metagenomics techniques were combined to separate maize rhizo-C utilizers from straw-C utilizers in agriculture soils containing both C sources. Also, by comparing bacterial utilizers and their C metabolisms in soils amended with a single C source (e.g., straw-¹³C only) and two C sources (e.g., straw-¹³C and rhizo-¹²C), we investigated the shift of composition and metabolisms of soil bacterial utilizers responding to C sources shift (e.g., compositional and metabolic changes of straw-¹³C utilizers from soil containing straw-¹³C to soil containing both straw-¹³C and rhizo-¹²C). We revealed i) Proteobacteria predominantly utilized rhizo-¹³C, while Firmicutes dominated the community specializing in straw-¹³C decomposition in soil containing both straw-C and rhizo-C; ii) the planted maize (i.e. rhizo-C input) changed community composition and metabolisms of straw-C utilizers, which shifted from K-strategists characterized by an enrichment of lignin-degrading genes to r-strategists which exhibited an enrichment of genes related to polysaccharide degradation. This metabolic shift of straw-C utilizer ultimately reduced straw-¹³C mineralization by 25.6% when maize was planted. This study identified the distinct utilizers of rhizo-C and straw-C in soils containing both C sources, and shed light on the shift of bacterial community and their metabolic activities responding to the changes of maize-derived C sources.