Altitude rather than season and slope aspect has the greatest effect on the bacterial communities in subtropical forests in Yunnan, China

Background and aims Altitude, season, and slope aspect have significant impacts on bacterial variation in forest soils. However, it is currently unclear which factor has the greatest influence. Methods Quantitative PCR (qPCR) and high-throughput sequencing were employed to investigate the changes in the bacterial communities with altitude, season and slope aspect in the subtropical forests of Mount Ailao. Results The effects of altitude, season and slope on bacterial abudance were in the order altitude (η 2 = 0.964) > season (η 2 = 0.831) > slope (η 2 = 0.590). In addition, the bacterial abundance increased with altitude, and the rainy season but not the dry season, the eastern slope rather than the western slope had a higher bacterial abundance. Furthermore, altitude (η 2 : 0.877–0.942) and season (η 2 : 0.229–0.761), resulted in higher bacterial α-diversity at low altitudes and in the dry season, respectively. Synergistetes/Verrucomicrobia (low altitude), Acidobacterium (high altitude), Actinobacteria/Planctomycetes (dry season) and Armatipnoadetes (rainy season) were the richest in the soils. Correlation networks showed that bacteria were very stable at higher altitudes and in the dry season. In addition, soil water content, soil organic matter, total nitrogen and ammonium nitrogen were the key edaphic factors significantly affecting the bacterial abundance, α-diversity, and β-diversity. Conclusions Altitudes rather than seasons and slope aspects had the greatest effect on the bacterial communities in subtropical forests. Therefore, we suggest that altitude, season, and slope aspect be considered necessary factors for comprehensive analysis when studying soil microbial changes in different forests. Graphical abstract