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.