Soil bacterial community responses to long-term fertilizer treatments in Paulownia plantations in subtropical China

The use of fertilizers to overcome nutrient constraints is standard practice in Paulownia fortunei plantations to increase stem wood production and tree yields. However, little is known about the responses and important role of the soil bacteria involved in the increases of soil fertility and standing volume with different fertilization. The 16S rRNA was used to compare four different fertilizer treatments for soil bacterial communities in three P. fortunei plantations, in Hunan Province, China. The results showed that the soil bacteria richness was significantly higher in plantations fertilized for ten years than for shorter times. The phyla Acidobacteria and Gemmatimonadetes were more prevalent for ten-year old plantations, and Firmicutes significantly increased with organic manure treatment (denoted as OM; p < 0.05). OM significantly increased the ratio of Bacilli-like sequences in Firmicutes to 87%, 97% and 78% in seven-, nine- and ten-year-old plantations, respectively (p < 0.05), while control and inorganic fertilizer had no effect. Principal coordinate analysis revealed that the soil bacterial communities in OM were different from the control and inorganic fertilizer in the three different plantations. Canonical correspondence analyses showed that available phosphorus and available magnesium were the most strongly related to bacterial community composition. The addition of OM led to soil being more fertile and an increased standing volume compared with the other fertilizer treatments. Bacilli, the most abundant class of Firmicutes may represent the bacterial type that responded most distinctly to organic manure fertilization and could be highly effective bacteria to increase soil fertility and achieve sustainable development of P. fortunei plantations.