Methane emissions from different vegetation zones in a Qinghai-Tibetan Plateau wetland Mitsuru Hirota a, * , Yanhong Tang b , Qiwu Hu c , Shigeki Hirata d , Tomomichi Kato a , Wenhong Mo e , Guangmin Cao c , Shigeru Mariko e a Doctoral Program in Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan b National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan c Northwest Plateau Institute of Biology, Chinese Academy of Science, Xining 810001, China d Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan e Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan Received 18 August 2003; received in revised form 15 December 2003; accepted 24 December 2003 Abstract We measured methane (CH 4 ) emissions in the Luanhaizi wetland, a typical alpine wetland on the Qinghai-Tibetan Plateau, China, during the plant growth season (early July to mid-September) in 2002. Our aim was to quantify the spatial and temporal variation of CH 4 flux and to elucidate key factors in this variation. Static chamber measurements of CH 4 flux were made in four vegetation zones along a gradient of water depth. There were three emergent-plant zones (Hippuris-dominated; Scirpus-dominated; and Carex-dominated) and one submerged-plant zone (Potamogeton-dominated). The smallest CH 4 flux (seasonal mean ¼ 33.1 mg CH 4 m 22 d 21 ) was observed in the Potamogeton- dominated zone, which occupied about 74% of the total area of the wetland. The greatest CH 4 flux (seasonal mean ¼ 214 mg CH 4 m 22 d 21 ) was observed in the Hippuris-dominated zone, in the second-deepest water area. CH 4 flux from three zones (excluding the Carex-dominated zone) showed a marked diurnal change and decreased dramatically under dark conditions. Light intensity had a major influence on the temporal variation in CH 4 flux, at least in three of the zones. Methane fluxes from all zones increased during the growing season with increasing aboveground biomass. CH 4 flux from the Scirpus-dominated zone was significantly lower than in the other emergent-plant zones despite the large biomass, because the root and rhizome intake ports for CH 4 transport in the dominant species were distributed in shallower and more oxidative soil than occupied in the other zones. Spatial and temporal variation in CH 4 flux from the alpine wetland was determined by the vegetation zone. Among the dominant species in each zone, there were variations in the density and biomass of shoots, gas-transport system, and root – rhizome architecture. The CH 4 flux from a typical alpine wetland on the Qinghai-Tibetan Plateau was as high as those of other boreal and alpine wetlands. q 2004 Elsevier Ltd. All rights reserved. Keywords: Methane flux; Zonal vegetation; Growth form; Water depth; Alpine wetland; Qinghai-Tibetan Plateau 1. Introduction Methane (CH 4 ) is an important greenhouse gas (Khalil and Rasmussen, 1983). The atmospheric CH 4 concentration has doubled since the industrial revolution (IPCC, 2001) and depends on the balance between sink and source for CH 4 . Wetlands account for about 70% of natural CH 4 sources (Khalil, 2000) and roughly 20% of the global CH 4 emission (IPCC, 2001). Previous studies have quantified CH 4 emissions from various wetlands in the world (Bartlett and Harriss, 1993), and have determined the factors controlling CH 4 flux (Wang et al., 1993; Schimel, 1995; Ding et al., 2003). However, global estimates of CH 4 emission from wetlands are still uncertain, because there is a lack of CH 4 flux data for specific wetlands and flux measurements have not included the spatial variability of CH 4 flux in relation to vegetation, climate, and topography (Schu ¨tz et al., 1991; Saarnio et al., 1997). In recent years, vegetation has been recognized as a key factor affecting spatial variation in CH 4 flux (Joabsson et al., 1999; Joabsson and Christensen, 2001). 0038-0717/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2003.12.009 Soil Biology & Biochemistry 36 (2004) 737–748 www.elsevier.com/locate/soilbio * Corresponding author. Tel./fax: þ 81-29-853-4531. E-mail address: s015586@ipe.tsukuba.ac.jp (M. Hirota).