Soil bacterial communities of different natural forest types in Northeast China

Background and aims: The types of natural forests have long been suggested to shape below-ground microbial communities in forest ecosystem. However, detailed information on the impressionable bacterial groups and the potential mechanisms of these influences are still missing. The present study aims to deepen the current understanding on the soil microbial communities under four typical forest types in Northeast Asia, and to reveal the environmental factors driving the abundance, diversity and composition of soil bacterial communities.

Methods: Four forest types from Changbai Nature Reserve, representing mixed conifer-broadleaf forest and its natural secondary forest, evergreen coniferous forest, and deciduous coniferous forest were selected for this study. Namely, Broadleaf-Korean pine mixed forest (BLKP), secondary Poplar-Birch forest (PB), Spruce-Fir forest (SF), and Larch forest (LA), respectively. Soil bacterial community was analyzed using bar-coded pyrosequencing. Nonmetric multidimensional scaling (NMDS) was used to illustrate the clustering of different samples based on both Bray-Curtis distances and UniFrac distances. The relationship between environmental variables and the overall community structure was analyzed using the Mantel test.

Results: The two mixed conifer-broadleaf forests (BLKP and PB) displayed higher total soil nutrients (organic carbon, nitrogen, and phosphorus) and soil pH, but a lower C/N ratio as compared to the two coniferous forests (SF and LA). The mixed conifer-broadleaf forests had higher alpha-diversity and had distinct bacterial communities from the coniferous forests. Soil texture and pH were found as the principle factors for shaping soil bacterial diversity and community composition. The two mixed conifer-broadleaf forests were associated with higher proportion of Acidobacteria, Verrucomicrobia, Bacteroidetes, and Chloroflexi. While the SF and LA forests were dominated by Proteobacteria and Gemmatimonadetes.

Conclusions: Different natural forest type each selects for distinct microbial communities beneath them, with mixed conifer-broadleaf forests being associated with the low-activity bacterial groups, and the coniferous forests being dominated by the so-called high-activity members. The differentiation of soil bacterial communities in natural forests are presumably mediated by the differentiation in terms of soil properties, and could be partially explained by the copiotroph/oligotroph ecological classification model and non-random co-occurrence patterns.