Salinity drives archaeal distribution patterns in high altitude lake sediments on Tibetan Plateau

1. Salinity drives archaeal distribution patterns in high altitude lake sediments on Tibetan Plateau Introduction Results and Discussion Diverse methanogenic lineages were present in all of the lake sediment samples and accounted for more than 50% of the total sequences in five of the lakes. The distribution patterns of three functional types of methanogens (putatively hydrogenotrophic, acetotrophic and methylotrophic) were influenced by salinity. The hydrogenotrophic methanogens decreased in abundance as salinity increased, while the trend was opposite for acetotrophic methanogens. Methylotrophs dominated the methanogenic groups in the hypersaline sediments where acetotrophic methanogens became less abundant (Fig.3), although they also existed in the non-saline sediments that were dominated by hydrogenotrophic and acetotrophic methanogens. Archaea play critical roles in global energy cycles and impact the global climate. The diversity and ecology of Archaea have received increasing attention. Globally, salinity is important in controlling archaeal distribution patterns, while controls on local scales vary across environments. However, the ecology of Archaea in the sediments of high mountain lakes has received less attention in spite of the greater archaeal diversity that may be characteristic of sediment habitats and the important roles of Archaea in biogeochemical cycles in lake sediments. Here, we investigated archaeal communities along a salinity gradient from the sediments of 20 different high altitude lakes across the Tibetan Plateau. The Tibetan Plateau is the highest plateau in the world, with an average height of 4000 m above sea level and encompasses a total lake area of more than 50,900 km2. The lakes of the Plateau are far from human habitation, and their pristine nature and range of geochemical conditions provide excellent conditions for studying the diversity and ecology of Archaea. To date, little is known about the archaeal community compositions in these pristine high altitude lake sediments. We used a high-resolution bar-coded pyrosequencing technique to describe the composition of archaeal assemblages across the Tibetan Plateau in the context of their different environmental conditions. The Tibetan Plateau lakes sediments contained diverse archaeal communities, which clustered into groups dominated by methanogenic Euryarchaeota, Crenarchaeota and Halobacteria /mixed euryarchaeal phylotypes (Fig.1). Community similarity (Fig. 2) and dominant community types (Fig. 1) grouped according to the salinity gradient. Sediments with the highest salinities (>15 g L-1) were usually dominated by Halobacteria .The Crenarchaeota dominated at intermediate salinities (0.3 to 19.5 g L-1), in contrast to previous studies, which found that Crenarcheota were most common in freshwater sediments. Yongqin Liu, Tandong Yao Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), 100085, Beijing, China Materials and methods Fig.3 Relative proportions of hydrogenotrophic, acetotrophic and methylotrophic methanogens relative to total archaea in each lake. Columns were arranged in decreasing order of the proportions of hydrogenotrophic methanogens. We investigated surface sediments from 20 lakes located along an east-west transect on the Tibetan Plateau. The lakes ranged from fresh, to saline to hypersaline. Community DNA was extracted from sediments. Aliquots (50 ng) of DNA were used as template for amplification of the hypervariable V3 regions of archaeal 16S rRNA with the archaeal specific primer Arch334F, Arch915R. PCR products were run on a Roche FLX 454 pyrosequencing machine. Data were processed using the QIIME pipeline. Taxonomic identity of each phylotype was determined using the Greengenes database. Conclusions Fig.1 Relative proportions of the archaeal lineages within each lake. Our study represents a comprehensive investigation of archaeal diversity in the pristine lake sediments across the Tibetan Plateau. The results document high diversity of methanogens, Crenarchaeota, Halobacteria, and Thermoplasmata. Methanogens occurred in sediments of all lakes, but the distribution patterns of the three functional groups of methanogens (hydrogenotrophic, acetotrophic and methylotrophic) were controlled by salinity. The cosmopolitan distribution of functionally diverse methanogens in these lakes indicates that they may be a significant source of CH4 and, when combined with the substantial input already calculated for Tibetan Plateau wetlands (450 Gg yr-1 (Ding et al., 2004)), the region may have significant impacts on global climate. Our study showed that salinity shaped the archaeal community composition on a regional scale spanning nearly two thousand kilometers on a high-altitude plateau. Fig.2 Nonmetric Multidimentsional Scaling (NMDS) of the archaeal communities based on Bray–Curtis distances of detected OTU abundances Address: 16#, Lincui Road, Chaoyang District, Beijing, 100101, ChinaTel: +86-10-8409-7122; E-mail: yqliu@itpcas.ac.cn