Identification of microbial strategies for labile substrate utilization at phylogenetic classification using a microcosm approach

Substrate utilization strategies of microorganisms modulate soil organic carbon (SOC) turnover, which is essentially regulated by the quality and quantity of exogenous substrate. However, a detailed understanding of the functional traits of different microbial taxa in substrate utilization is limited. Therefore, an 8-week microcosm amendment of the weekly addition of 13C-glucose was performed on an Ultisol to link the phylogenetic classification of microbial taxa with their activation via the use of exogenous labile carbon (C). Temporal variations in glucose-C assimilation of bacterial and fungal groups were characterized using the combined application of nucleic acid stable isotope probing and high-throughput pyrosequencing techniques. The stimulation of glucose on the growth of soil microorganisms was time-dependent, with a rapid response of bacteria and a succession to fungal proliferation. The preference of C sources of bacterial phyla was definitely controlled by the life-history of trophic pattern, and the copiotrophic bacterial phyla remained in stronger competitiveness for labile C compared to the oligotrophic phyla. These substrate utilization strategies primarily originated from the genus level with phylogenetically conserved attributes despite the increased number of functional executors with the increasing C availability. In contrast, all of the detected fungi in the incubation microcosm used labile C and possible the native soil organic matter from the phylum to genus level, which was primarily ascribed to the wide spectrum of substrate utilization of fungal taxa. The distinct substrate utilization strategies of bacteria and fungi have important implications in the elucidation of their functional traits involved in SOC turnover. •Labile C shaped bacterial and fungal substrate utilization strategy.•Bacteria retained labile C specificity in their natural assemblages.•Bacterial substrate preference originated at genus and scaled up to the phylum level.•Individual fungi used labile C and native SOC at all taxonomic levels.•Fungi showed a wide spectrum of substrate utilization strategies.