Comparative analysis of soil microbial communities and their responses to the short-term drought in bog, fen, and riparian wetlands Seon-Young Kim a, d , Seung-Hoon Lee c , Chris Freeman b , Nathalie Fenner b , Hojeong Kang c, * a Department of Environmental Science and Engineering, Ewha Womans University, Seoul 120-750, Republic of Korea b School of Biological Sciences, University of Wales, Bangor LL 2UW, UK c School of Civil and Environmental Engineering, Yonsei University, Seoul 120-749, Republic of Korea d Institute of Applied Sciences, University of North Texas, Denton, TX 76203, USA article info Article history: Received 27 November 2007 Received in revised form 1 August 2008 Accepted 6 August 2008 Available online 1 September 2008 Keywords: Bog Denitrifiers Drought Eubacterial community Fen Methanogens Real-time PCR Riparian wetland T-RFLP abstract The frequency of drought is anticipated to increase in wetland ecosystems as global warming intensifies. However, information on microbial communities involved in greenhouse gas emissions and their responses to drought remains sparse. We compared the gene abundance of eubacterial 16S rRNA, nitrite reductase (nirS) and methyl coenzyme M reductase (mcrA), and the diversity and composition of eubacteria, methanogens and denitrifiers among bog, fen and riparian wetlands. The gene abundance, diversity and composition significantly differed among wetlands (p < 0.01) with the exception of the diversity of methanogens. The gene abundance was ranked in the order of the bog ¼ fen > riparian wetland, whereas the diversity was in the riparian wetland  fen > bog. In addition, we conducted a short-term drought experiment and compared microbial communities between control (water-logged) and drought (15 cm) treatments. Drought led to significant decline in the gene abundance in the bog (16S rRNA, nirS, mcrA)(p < 0.01) and fen (16S rRNA, nirS)(p < 0.05), but not in the riparian wetland. There were no differences in the diversity and composition of denitrifiers and methanogens at all sites following drought. Our results imply that denitrifiers and methanogens inhabiting bogs and fens would suffer from short-term droughts, but remain unchanged in riparian wetlands. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Climate change models suggest that environmental pressures on ecosystems will increase as global warming intensifies (Manabe and Wetherald, 1986; Houghton et al., 2001). In particular, drought is likely to exert a major influence on wetlands, northern peatlands in particular, which function as a major global sink for CO 2 (Gitay et al., 2001). Substantial C losses have been already reported from boreal and sub-arctic bogs and fens due to lower water levels during warm and dry summers (Schreader et al., 1998; Alm et al., 1999; Moore et al., 2002). Concerns have been raised that frequent drought could reduce the capacity of wetlands to function as sinks for global C, or eventually turn them into sources of atmospheric C. Wetland soils undergo intermittent flooding and draining, thus supporting both aerobic and anaerobic microbial communities. In particular, such variation is highly depth-dependent, because surface layers experience fluctuation of water level more frequently compared with deeper layers. These diverse microbial communities may exploit a wide range of electron acceptors during organic matter decomposition and may contribute significantly to green- house gas emissions from wetlands. For instance, denitrifiers mediate a respiratory process (i.e. denitrification) in which oxidized nitrogen compounds are used as alternative electron acceptors when oxygen is limited, leading to NO and N 2 O emissions (Hoch- stein and Tomlinson, 1988). Methanogens are involved in the terminal respiration processes (i.e. methanogenesis) in which organic matters are degraded completely to CO 2 and CH 4 when electron acceptors like oxygen, nitrate, iron oxides and sulfate have been depleted (Thauer, 1998). Those gases (e.g. NO, N 2 O, CH 4 and CO 2 ) produced through anaerobic or aerobic processes are potent greenhouse gases that contribute to global worming. Thus knowl- edge on denitrifiers and methanogens in wetlands and their responses to drought will ultimately help us better understand and manage ecological functions of wetlands in terms of organic matter decomposition and greenhouse gas emissions (Boon et al., 1997). Past studies have consistently reported decreases in the CH 4 emissions, and increases in the CO 2 emissions due to enhanced aerobic decomposition in the peatlands following droughts (Freeman et al., 1992; Ratering and Conrad, 1998; Dowrick et al., 2006). Lowering of the water table generally increased the N 2 O * Corresponding author. Tel.: þ82 2 2123 5803; fax: þ82 2 364 5300. E-mail address: hj_kang@yonsei.ac.kr (H. Kang). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2008.08.004 Soil Biology & Biochemistry 40 (2008) 2874–2880