Rearrangement of bacterial community structure during peat diagenesis

Abstract

The relationship between microbial diagenesis of Sphagnum peat (SP) and reed-sedge peat (RSP) and the spatial organization of peat bacterial communities was studied. Peats were aerobically incubated at 18–22 °C for 4 months. Changes in molecular composition of peat organic matter were monitored with solid-state 13C NMR, and the respective amount of functional groups was determined by integration of corresponding peaks. No abiotic peat transformation was detected. SP diagenesis caused about a 4% loss of parent materials with a similar yield of ketones, phenols, aromatic, and carbonyl compounds; whereas about 20% of RSP carbohydrates, along with ketones and methoxyl compounds were gradually transformed into carbonyl and aliphatic compounds. SP and RSP substantially varied in bacterial composition. To address spatial community structure, bacterial populations were dissected by a differential elution technique into three fractions based on the degree of their attachment to peat. Community composition was surveyed with T-RFLP ( HhaI, MspI, and RsaI). The fragments were further attributed to freely-dispersed (FD), particle-associated (PA), or omnipresent (OMN) bacterial fractions. In both peats, bacterial communities have gradually shifted with the progress of diagenesis. In SP, numbers of exclusively FD or PA bacteria slightly decreased while in RSP their numbers more than doubled after 4-month incubation, and the number of OMN bacteria respectively decreased. The substantially greater changes in the spatial structure of RSP bacterial community compared to SP were consistent with the chemical transformations detected in these peats suggesting the diagenesis-driven divergence of RSP bacterial community into FD and PA sub-communities.