Comparison of diversities and compositions of bacterial populations inhabiting natural forest soils

Abstract

The diversity and composition of soil bacterial communities were compared among six Austrian natural forests, including oak-hornbeam, spruce-fir-beech, and Austrian pine forests, using terminal restriction fragment length polymorphism (T-RFLP, or TRF) analysis and sequence analysis of 16S rRNA genes. The forests studied differ greatly in soil chemical characteristics, microbial biomass, and nutrient turnover rates. The aim of this study was to relate these differences to the composition of the bacterial communities inhabiting the individual forest soils. Both TRF profiling and clone sequence analysis revealed that the bacterial communities in soils under Austrian pine forests, representing azonal forest types, were distinct from those in soils under zonal oak-hornbeam and spruce-fir-beech forests, which were more similar in community composition. Clones derived from an Austrian pine forest soil were mostly affiliated with high-G+C gram-positive bacteria (49%), followed by members of the alpha-Proteobacteria (20%) and the Holophaga/Acidobacterium group (12%). Clones in libraries from oak-hornbeam and spruce-fir-beech forest soils were mainly related to the Holophaga/Acidobacterium group (28 and 35%), followed by members of the Verrucomicrobia (24%) and the alpha-Proteobacteria (27%), respectively. The soil bacterial communities in forests with distinct vegetational and soil chemical properties appeared to be well differentiated based on 16S rRNA gene phylogeny. In particular, the outstanding position of the Austrian pine forests, which are determined by specific soil conditions, was reflected in the bacterial community composition.

FIG. 1.

Representative TRF profiles of bacterial communities from mineral soils under three Austrian natural forests: oak-hornbeam forest (A), spruce-fir-beech forest (B), and Austrian pine forest (C). Fragments corresponding to dominant phylogenetic groups represented by 16S rRNA gene clones derived from the same soils are indicated and labeled with the respective peak heights.

FIG. 2.

Score plot (A) and loading plot (B) of PCA of TRF data. In the loading plot, only fragments with heights of ≥300 FU are shown. •, oak-hornbeam forest (Johannser Kogel); ○, oak-hornbeam forest (Kolmberg); ▴, spruce-fir-beech forest (Rothwald); ▵, spruce-fir-beech forest (Neuwald); ▪, Austrian pine forest (Stampfltal); □, Austrian pine forest (Merkenstein).

FIG. 3.

Dendrogram of TRF profiles from six natural forest soils generated from Euclidean distance values, using the UPGMA method. Cluster analysis was performed with average TRF values of 10 individual subsamples from the study sites. JE, Johannser Kogel; K, Kolmberg; R, Rothwald; N, Neuwald; St, Stampfltal; Me, Merkenstein.