Differences in the activity and bacterial community structure of drained grassland and forest peat soils Luka Ausec, Barbara Kraigher, Ines Mandic-Mulec * Biotechnical Faculty, Department of Food Science and Technology, University of Ljubljana, Jamnikarjeva 101,1000 Ljubljana, Slovenia article info Article history: Received 3 December 2008 Received in revised form 1 June 2009 Accepted 12 June 2009 Available online 8 July 2009 Keywords: Drained peat soil Soil pH Substrate-induced respiration T-RFLP Bacterial community structure 16S rRNA genes Acidobacteria Diversity abstract The microbial activity and bacterial community structure were investigated in two types of peat soil in a temperate marsh. The first, a drained grassland fen soil, has a neutral pH with partially degraded peat in the upper oxic soil horizons (16% soil organic carbon). The second, a bog soil, was sampled in a swampy forest and has a very high soil organic carbon content (45%), a low pH (4.5), and has occasional anoxic conditions in the upper soil horizons due to the high water table level. The microbial activity in the two soils was measured as the basal and substrate-induced respiration (SIR). Unexpectedly, the SIR (ml CO 2 g 1 dry soil) was higher in the bog than in the fen soil, but lower when CO 2 production was expressed per volume of soil. This may be explained by the notable difference in the bulk densities of the two soils. The bacterial communities were assessed by terminal restriction fragment length poly- morphism (T-RFLP) profiling of 16S rRNA genes and indicated differences between the two soils. The differences were determined by the soil characteristics rather than the season in which the soil was sampled. The 16S rRNA gene libraries, constructed from the two soils, revealed high proportions of sequences assigned to the Acidobacteria phylum. Each library contained a distinct set of phylogenetic subgroups of this important group of bacteria. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Marshes and other types of wetlands are globally important as reservoirs of soil organic carbon (SOC), and are locally important as hydro-regulators and biodiversity hotspots. These wetlands cover approximately 3% of the land-surface, store up to 30% of the Earth’s terrestrial carbon and play a vital role in carbon cycling (Gorham, 1995). Their biomass production exceeds decomposition due to low pH and the anoxic conditions often found in the soil, caused by high ground water or flooding (Augustin et al., 1996). Despite the fact that bacteria play a major role in the turnover of energy and matter in the soil, there have been only a few attempts to study the bacterial diversity in the peat soils (Dedysh et al., 2006; Kraigher et al., 2006; Morales et al., 2006). Terminal restriction fragment length polymorphism (T-RFLP) analysis of 24 bogs in the USA revealed a high bacterial diversity with a marked similarity among the sites (Morales et al., 2006). The composition of the bacterial community was also studied in a Siberian peat bog (Dedysh et al., 2006). Data from that study showed that the largest number of sequences (24 out of 84) in the 16S rRNA gene library was from the recently described phylum, Acidobacteria. When counted by fluorescent in situ hybridization (FISH), Acidobacteria comprised 0.1–4.1% of the total bacterial cell number in nine different Sphagnum-dominated bogs in Northern Russia (Pankratov et al., 2008). Other studies on the bacterial diversity and activity in peat soil have focused on specific taxonomic (e.g., Actinobacteria, Rheims et al., 1996) or functional groups, e.g., methanogenic archaea (Basiliko et al., 2003; Horn et al., 2003) and methanotrophic bacteria (Dedysh et al., 2001). In addition to the northern peat soils, Acidobacteria were also dominant in the Alaskan acidic soils, rep- resenting approximately 40% and 30% of clones in the tussock and intertussock soil clone libraries, respectively. However, Acid- obacteria were poorly represented in the shrub organic and mineral soils from the same area, which were dominated by Proteobacteria (Wallenstein et al., 2007). Little is known about the microbial communities in the temperate bogs and fens. Usually these marshes have been subject to drainage and altered land use and therefore the microbial communities might not follow the patterns observed in the rela- tively undisturbed marshes of the high latitudes. The aim of this study was to investigate the microbial activity and bacterial community structure in a temperate marsh. These soils have been * Correspondence to: Ines Mandic-Mulec, Biotechnical Faculty, Department of Food Science and Technology, University of Ljubljana, Chair of Microbiology, Vecna pot 111, 1000 Ljubljana, Slovenia. Tel.: þ386 1 4233388; fax: þ386 1 257 3390. E-mail address: ines.mandic@bf.uni-lj.si (I. Mandic-Mulec). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2009.06.010 Soil Biology & Biochemistry 41 (2009) 1874–1881