4.1 Soil bacterial community α diversity and its influencing factors
The results of this study support the first hypothesis that SF has higher soil bacterial community diversity than PB. The values of Sobs, Chao, and ACE, which reflect the richness of the soil bacterial community, and the values of the Shannon and Pd indices, which reflect the diversity of the community, in SF were significantly higher than those in PB, indicating that the diversity of the soil bacterial community in SF was significantly higher than that in PB (Fig. 2). Our research also found that the values of Sobs, Chao, ACE and Pd in CSF were significantly lower than those in SF and were significantly higher than those in PB. This shows that, in terms of soil bacterial community diversity, CSF is located between SF and PB. Long-term drainage and construction of the Cryptomeria fortunei forest significantly reduced the soil bacterial community diversity of SF and significantly increased the soil bacterial community diversity of PB. The number of bacterial taxa observed at the genus, family, class and phylum levels in various types of sites also exhibited similar patterns. A total of 348 genera, 252 families, 81 classes and 32 phyla were found in SF soil bacteria; 258 genera, 190 families, 54 classes and 23 phyla were found in CSF soil bacteria; 227 genera, 169 families, 52 classes and 23 phyla were found in PB soil bacteria; and SF soil bacteria had many unique groups at the genus, family, class and phylum levels (Fig. 3). The above analysis shows that, compared with PB and CSF, SF has rich soil bacterial diversity and high uniqueness, so it is very important to protect and restore this type of wetland.
The results of this study showed that most indices reflecting the richness and diversity of soil bacterial communities were significantly positively correlated with soil pH and SWW and negatively correlated with AP, suggesting that soil pH, SWW and AP were important factors affecting the α diversity of soil bacterial communities (Table 1). Hartman et al. (2008) conducted a comprehensive analysis of various types of wetlands in the United States and found that soil bacterial community diversity was closely related to soil pH, and soil pH predicted the diversity of phyla and species at all the sites they studied. Urbanová and Bárta (2014) reported a significant increase in species richness and diversity in Czech peatlands from natural fen and spruce forest swamps to bogs, reflecting changes in peat pH, nutrient availability, and peat decomposition ability and that the higher the pH, the higher the species richness and diversity. Urbanová and Bárta (2016) found in their study of Czech peatlands that the pH values of fen and spruce forest swamps significantly decreased after long-term drainage, and species richness and diversity significantly decreased. These studies all support that the pH value of peatland soil is an important factor affecting the diversity of soil bacterial communities. This study found that SWW and AP were significantly positively correlated and extremely significantly negatively correlated with the pH value, respectively, indicating that soil pH is the best predictor of soil bacterial community diversity (Fig. S1) (Fierer et al. 2008; Hartman et al. 2008). AP was significantly higher in PB (Fig. 1D), which may be related to the Ericaceae plant Gaultheria hookeri . It is known that Ericaceae plants can form ericoid mycorrhizal symbionts with soil fungi. These symbionts can mobilize N and P complexes in recalcitrant organic matter, promote plant absorption, and lead to an increase in the concentration of phosphorus in soil solution (Kaštovská et al. 2018; Perotto et al. 2018). This is also an important factor for Ericaceae plants to survive and even dominate in poor, acidic and other harsh environments.
This study shows that long-term drainage and construction of theCryptomeria fortunei forest significantly reduce the diversity of the soil bacterial community in SF and significantly increase the diversity of the soil bacterial community in PB. Therefore, restoring peatland to its natural SF state, which is affected by long-term drainage and afforestation, will increase soil microbial diversity, while restoring peatland to its natural PB state will reduce soil microbial diversity. Urbanová and Bárta (2016) found similar results in their long-term drainage study of peatlands in the Czech Republic, where long-term drainage significantly reduced the diversity of soil bacteria in fens and significantly increased the diversity of soil bacteria in bogs. Hartman et al. (2008) studied three types of wetlands in North Carolina, USA, and found that restoration of wetlands from agricultural use reduced soil bacterial diversity. This suggests that unlike terrestrial ecosystem restoration, which generally increases diversity (DeGrood et al. 2005; Mckinley et al. 2005), wetland restoration does not necessarily increase soil bacterial diversity, depending on the type of disturbance and the type of wetland.