Diversity and Functional Potential of Soil Bacterial Communities in Different Types of Farmland Shelterbelts in Mid-Western Heilongjiang, China

The diversity and function of surface soil bacterial community in farmland shelterbelts of five forest types and one abandoned wilderness area were analyzed by collecting 36 soil samples at depths of 0-10 cm (the upper soil layer) and 10-20 cm (the lower soil layer), extracting DNA from the samples and amplifying and sequencing the bacterial 16S rDNA V3V4 region. Dominant bacterial phyla in forest soils included the Actinomycetes, Proteobacteria, Acidobacteria, Chlorobacteria, and Bacillus. The number of unique bacterial OTUs (operational taxonomic units) was higher in the upper versus lower soil layer and greater in the abandoned cropland than in the shelterbelts. The number of total bacterial OTUs was highest in the mixed Pinus sylvestris var. mongholica Litv. and Larix gmelinii (Rupr.) Kuzen. forest. At the phyla level, Actinomycetes showed the greatest variation in abundance among forest types, while at the genus level, Actinoplanes varied most among forest types in the upper soil layer and Krasilnikovia varied most in the lower soil layer. Soil bacteria were more strongly correlated and more intense competition in the upper soil layer than in the lower soil layer; Actinoplanes and Krasilnikovia were key genera in bacterial networks. Functional predictions for bacterial community genes indicated that soil fertility potential was strong in the mixed Fraxinus mandshurica Rupr. and Larix gmelinii (Rupr.) Kuzen. forest, weak in the mixed Pinus sylvestris var. mongholica Litv. and Larix gmelinii (Rupr.) Kuzen. forest, and in the Populusxxiaohei forest, and intermediate in the Larix gmelinii (Rupr.) Kuzen. and Pinus sylvestris var. mongholica Litv. forests. This study provides a new theoretical basis for the sustainable management of soil fertility in the agroforestry system.