Strong elevational trends in soil bacterial community composition on Mt. Halla, South Korea

Elevational trends in the ecology of macroorganisms have been studied extensively; by contrast very little is known of such trends in microbial diversity. Previous studies on soil bacteria have found either a diversity decline, a ‘peak’ in mid altitudes, or no trend with increasing elevation. Here we studied bacterial diversity and community composition in relation to elevation on Mt. Halla, Jeju Island, South Korea, a massive shield volcano. Samples were taken along two transects, from 100 m.a.s.l. to the summit at 1950 m.a.s.l., at elevational intervals of 200 m. PCR-amplified soil DNA for the bacterial 16S rRNA gene targeting V1 to V3 region was 454-pyrosequenced, and taxonomically classified against EzTaxon-e database. ion was the best predictor of variation in bacterial community composition along the two transects, even when considering other soil parameters. Elevation was itself highly correlated with mean annual temperature (MAT) and mean annual precipitation (MAP), suggesting that soil bacterial community composition on Mt. Halla is more strongly affected by climate than by geochemical or soil textural factors. The two transects showed certain consistent differences in bacterial phyla composition, with one transect having significantly higher abundance of Planctomycetes and Gemmatimonadetes than the other. Certain other phyla (e.g. Acidobacteria) also showed striking trends in abundance with elevation, but the trends differed between the two transects. ial diversity and richness were also most strongly correlated with elevation, MAT and MAP, although soil pH explained a part of the variation. Moreover, vegetation cover type, irrespective of elevation, had an effect on soil bacterial diversity and richness. We found a ‘dip’ in diversity at lower mid elevations (700–1300 m) in both transects; a trend which has not been found before. Our results, when compared with other studies, emphasize that no simple rule can be applied to mountain systems in general, but that climate itself is a major influence on community composition.