Tracing carbon flow from microphytobenthos to major bacterial groups in an intertidal marine sediment by using an in situ 13C pulse-chase method

摘要

Carbon flow from benthic diatoms to heterotrophic bacterial was traced in an intertidal sediment for 5consecutive days. 13C-labeled bicarbonate was sprayed onto the sediment surface during low tide and 13C-labelincorporation in major carbon pools, intermediate metabolites, and biomarkers were monitored. Phospholipidderivedfatty acid (PLFA) and ribosomal ribonucleic acid (rRNA) were used to identify the responsible membersof the microbial community at class and family phylogenetic resolution. Diatoms were the predominant primaryproducers, and Gammaproteobacteria, Bacteroidetes, and Deltaproteobacteria (21%, 8%, and 7% of 16S rRNAderivedclone library) were major heterotrophic bacterial groups. Both 13C-PLFA and 13C-rRNA data suggest afast transfer of label from diatoms (60 nmol 13C g21 dry weight [dry wt]) to bacteria (7 nmol 13C g21 dry wt)during the first 24 h, which was probably due to the exudation of low-molecular-weight organic compounds bydiatoms that could be directly utilized by bacteria. After this initial fast transfer, labeling of bacteria proceeded ata slower rate to 13 nmol 13C g21 dry wt on the third day of the experiment, which coincided with the degradationof carbohydrates in water-extractable extracellular polymeric substances (EPS) initially produced by the diatoms.Water-extractable EPS (primarily as glucose) was a major intermediate and its turnover explained 75% of thetotal carbohydrate processing in the sediment. Labeling in bacteria tracked labeling in the diatoms, suggesting aclosely coupled system. The heterotrophic bacterial groups benefited equally from the organic matter released bythe diatoms, suggesting limited specialization in this microbial food web.