Impact of long-term fertilization practices on the abundance and composition of soil bacterial communities in Northeast China

Soil bacterial communities mediate a wide range of ecosystem processes. In agricultural systems these processes determine soil health through bacterial roles in residue decomposition, nutrient cycling and their associations with other organisms. In this study, we investigated the abundance and composition of native soil bacterial communities under different long-term fertilization practices using quantitative real-time polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE). Soil samples were taken from a 20-year fertilization trial at the Plastic-film Mulching Experiment Station in Northeast China, which including four treatments of control (CK), inorganic-N fertilizer amendment (N), organic manure amendment (M), and half fertilizer-N plus half organic manure (M + N), to identify the difference of soil bacterial community under inorganic fertilizer and manure amendment. The size of the general bacterial population in the N treatment was significantly smaller than those in the CK, M and M + N treatments. Soil bacterial 16S rRNA gene copy numbers were positively correlated with soil pH and total organic carbon (TOC) content. The DGGE band patterns in CK, M and M + N treatments demonstrated more similarly to each other than to those of soil with only N amendment, while canonical correspondence analysis (CCA) revealed that the bacterial community structure in the N treatment was significantly different from the treatments of CK and M bacterial community profiles. Phylogenetic analysis of bands excised from the DGGE gels identified seven major phyla (Acidobacteria, Bacteroidetes, Gemmatimonadetes, Proteobacteria, Actinobacteria, Gammaproteobacteria and Firmicutes) present in all the treatments except the N treatment, in which no Gammaproteobacteria was observed. Results from this study suggest that agricultural fertilization practices have a great impact on soil bacterial community size and structure.