Bacterial community diversity in undisturbed perhumid montane forest soils in Taiwan

The diversity and composition of soil bacterial communities in three topographic sites (summit, foot slope, and lakeshore) from subtropical montane forest ecosystem in Taiwan were examined by using 16S rRNA gene clone library analysis. This locality is temperate, perhumid, and has low soil acidity (pH < 4), which is an uncommon ecosystem in a monsoonal part of Southeast Asia. A total of 481 clones were sequenced and placed into ten phylogenetic groups according to their similarities to type strains of described organisms. Toposequence of the transect was investigated from summit to foot slope and at the lakeshore. More than 86% of the clones were affiliated with members of the Proteobacteria, Acidobacteria, and Actinobacteria. Within the Proteobacteria, the beta-Proteobacteria was the most abundant, then alpha-Proteobacteria and gamma-Proteobacteria. Based on the Shannon diversity index (H) analysis, the bacterial community in the foot slope was the most diverse (H = 0.86) and that in summit was the least diverse (H = 0.68). The composition and diversity of soil bacterial communities in the three sites suggested no trend with topographic change. Less than 20% of the sequences were Acidobacteria-affiliated clones. The low proportion of Acidobacteria observed may be related to the high soil moisture and anaerobic microhabitats. Moreover, Shannon diversity indices revealed these bacterial communities to have lower diversity than that of other temperate (H = 0.90) and tropical forest (H = 0.82) ecosystems. The extreme acidity of soil pH and high soil moisture of this forest may explain composition and reduced the diversity of these soil bacterial communities.