Temporal variation of rhizodeposit-C assimilating microbial communities in a natural wetland

The objective of this study was to apply phospholipid fatty acid (PLFA)-based stable isotope probing to assess the temporal variation of active microorganisms associated with rhizosphere-C flow in a natural wetland. We applied (CO2)-C-13 pulse labeling at three different times throughout the vegetation period: spring (April), early summer (June), and early autumn (October). Soil redox potentials (Eh) at 10 cm depth ranged from moderately reduced (October) to oxidized conditions (June). Based on combined PLFA relative abundance and C-13 enrichment results, we suggest that gram-negative bacteria play a main role in rhizodeposit-C uptake in these wetland ecosystems, especially when reduced soil conditions prevail in October. Arbuscular and saprotrophic fungi also take up a significant proportion of the belowground allocated C, though mostly in the summer period. Gram-positive bacteria showed only a minor reliance on rhizodeposit-C throughout the year. It is concluded that rhizodeposit-C-assimilating microbial communities are heterogeneous and temporal variable entities with groups that are capable of adapting differently to seasonally varying environmental conditions.