The variations in soil microbial communities, enzyme activities and their relationships with soil organic matter decomposition along the northern slope of Changbai Mountain

• The F/B, G+/G− ratios increased with altitude.
• The soil microbial communities (SMC) were different along the elevational gradient.
• Soil enzyme activities in lower altitude were higher than those in higher altitude.
• The SMC were driven mainly by climatic factors but enzyme activity by soil nutrient.
• The SOM decomposition rate significant positively related with PLFAs.

We present a comprehensive analysis of the changes in the structure and functioning of the soil microbial communities, as well as their driving factors along the northern slope of Changbai Mountain by analyzing soil phospholipid fatty acids (PLFAs) profiles and enzymatic activities. The four vertical zones of vegetation selected in this study were as follows: (1) mixed coniferous and broad-leaved forest (MCB) located below 1100 m (site A and B); (2) dark-coniferous spruce-fir forest (DCF) located between 1100–1700 m (site C); (3) Ermans birch forest (EB) located between 1700 and 2000 m (site D); and (4) alpine tundra (AT) located above 2000 m (sites E and F). The results showed that the total viable microbial PLFAs varied with altitude, with the highest value detected in the EB (site D) (76.8 nmol g−1). The fungal/bacterial (F/B) and the Gram positive/Gram negative (G+/G−) ratios increased with elevation. The lower values of F/B obtained in the MCB (site A) and in DCF (site C) for G+/G－. The soil microbial community structure observed in the MCB (sites A and B) was different from that observed in the other four sites, with lower fungal biomass. The soil microbial activities such as β-glucosidase (βG), N-acetylglucosaminidase (NAG), acid phosphatase (AP) and leucine aminopeptidase (LAP) in the MCB (sites A and B) were significantly higher than those documented in the other four sites. The substantial differences in the soil microbial community composition were significantly correlated with the mean annual temperature (MAT), the mean annual precipitation (MAP) and soil temperature, silt and clay fraction, total phosphorus, nitrate nitrogen. However, the variations in soil enzyme activities were significantly correlated with soil nutrients. The MAP and nitrate nitrogen were the significant predictors of the variance in the soil microbial community and enzyme activity, respectively. The soil organic matter (SOM) decomposition rate showed a significant positive relationship with the total microbial, bacterial, actinomycetes PLFAs and the soil enzyme activities. Our results suggest that studies incorporating the microbial community structure and soil enzyme activity with the SOM decomposition may enhance our understanding of the mechanisms of biogeochemical processes.