메타지노믹스를 이용한 스발바드 지역의 토양 미소동물 군집 연구

Abstract

Little is known of the diversity, community structuring, niche differentiation and habitat specialization of small soil Metazoa in polar environments. Here, I studied three contrasting high arctic tundra types at Kongsford, NW Svalbard (78° 55 N), comparing the small soil Metazoa community in each along with the comparison to a mid-latitude temperate forest site in Korea (37 deg.N), using an identical interrupted grid sampling scheme. In addition, communities of nematode present in local microsites (rhizosphere, cyanobacterial mat, etc.) in the arctic tundra were also compared. Soil Metazoa, mostly nematodes were extracted using combined Baermann funnel and sugar flotation, and the DNA extracted, PCR amplified for the NF1-18Sr2b region of the 18s rRNA gene, and 454 pyrosequenced. Our samples revealed diverse communities of soil Metazoa in all three tundra types, with species proxy (operational taxonomic unit, [OTU]) diversity far exceeding the species diversity based on morphological surveys in previous studies of Svalbard. There was no difference in OTU α-diversity between the three tundra types. I found no correlation between nematode and soil properties but across individual samples there was a positive correlation between Shannon α-diversity with TOC, C/N ratio and P2O5. β-diversity was significantly higher in IV and LV tundra, suggesting that their mosaic of bare and vegetated patches supports a greater range of local metazoan communities than the more uniformly vegetated HV tundra. HV tundra had a distinct community from the LV tundra type, with the community of IV tundra falling between these in terms of OTU composition, indicating an important element of niche and habitat differentiation amongst small soil Metazoa between the three different tundra types. Different microsite types were differentiated at some degree based on NMDS resulted from Bray Curtis similarity matrix. The strongest differences were between rhizophere and cyanobacterial mat areas, and this pattern was consistent for Nematoda and for all Metazoa combined. However, no distinct community composition of the Metazoa was found within the microsites (e.g. between the rhizosphere of two different cushion plant species) suggesting the limits of microhabitat specialization in this environment. Overall, total nitrogen, total organic carbon and available phosphorus in the soil in each microsite were the best predictor of variation in both total metazoan and nematode communities. Despite the evidence of niche specialization in the communities, there was only about 5.56% of overlap in OTUs shared among different microsites suggesting that many species are actually quite generalized in their distribution and most likely in their ecology. However, I concluded that despite this being an extreme environment amongst land ecosystems, normally thought to require generalized niches amongst animals, the Metazoa in the high arctic tundra are still to some extent habitat-specialized. When the Svalbard tundra was compared with temperate forest, arctic tundra had markedly lower alpha-diversity for soil Metazoa than the temperate forest, reinforcing the view that there may be a classic latitudinal diversity difference in this group. However, two of the three sites in the Svalbard tundra had higher beta diversity than the Korean temperate forest, while a third tundra site has equally high beta diversity. This may reflect the greater influence of small scale environmental heterogeneity within the tundra compared to temperate forest. Also of interest is the fact that while most Metazoa OTUs in the temperate forest did not occur in the tundra, and vice versa, reflecting the degree of geographical endemism or environmental specialization that differentiates these regions. However, a small proportion (around 10%) of species do apparently occur in both environments despite their very distinct environments.