## 4 Discussion  
The purpose of this work was to investigate and analyze the response of microbial community structure under heavy PAH pollution stress by planting _E.purpurnea_. The contents of total PLGA in C and S groups decreased in 0-60 days. This was due to the inhibitory effect of PAHs on microorganisms. For the inhibition effect, _E.pururea_ relieved the stress of PAHs and increased the total amount of PLFAs in the soil, and the effect was significant at 120 days (\(p<0.05\)). The inhibitory effect of PAHs on microorganisms was mainly due to their strong adsorption capacity in the soil and low solubility, which limits the life activities of soil microorganisms. This is consistent with the view of  
Figure 1: PCA analysis chart. The horizontal axis is the first principal component (PC1), and the vertical axis is the second principal component (PC2). C indicates that _E.pururea_ was not planted, and S indicates that _E.purpurnea_ was planted. C0, C60, C120, C150, S0, S60, S120, and S150 represent soil samples at 0, 60, 120, and 150 days before and after planting, respectively. Figure 2: Changes in the total amount of phospholipid fatty acids associated with AMF (**A**) and Gram-negative bacteria (**B**) in the rhizosphere soil under high levels of PAH pollution. C, nonplanted; S, planted. Bars (means \(\pm\) SD, \(n=3\)) with different letters indicate the difference between samples in the same period (\(p<0.05\)). [PERSON] et al. (2019) [27]. _E. purpurea_ promotes microbial growth through plant roots. This is because the root system of plants is an important factor that affects the changes in the rhizosphere microbial community. Especially during the development of plants, changes in the rhizosphere will lead to the rapid growth of certain microbial populations and affect the choice of survival opportunities for other species [28]. Studies by [PERSON] et al. (2004) and [PERSON] et al. (2011) confirmed that under contaminated soil conditions, the plant roots can create more favorable living conditions for microorganisms to perform degradation, due to maintaining aerobic conditions in the rhizosphere, thereby promoting the degradation of organic matter [29,30]. The highest total amount of PLFAs appeared at 120 days. We believe that this result is closely related to the degradation of PAHs by _E. purpurea_. Relevant research shows that _E. purpurea_ has a good remediation effect on PAHs in contaminated soil. After 120 days, the degradation rate of PAHs was the highest, reaching 86.57% to 99.39%, which was 33.24% to 61.20% higher than that of unplanted soil [9]. It was found in the experiment that the counts of bacteria and fungi changed to different degrees before and after planting _E. purpurea_ and showed significant differences at 120 days (\(p<0.05\)). Analysis of changes in bacteria and fungi showed that _E. purpurea_ can alleviate the inhibitory effect of PAHs and stimulate them through rhizosphere exudates. With the degradation of PAHs, the available effective carbon sources in the soil increase, which is conducive to the growth of bacteria. Relevant research shows that the degradation of rhizosphere microorganisms is the main factor in the removal of PAHs. Microbial populations use organic compounds as a carbon substrate to grow, and this process is usually stimulated by plant rhizosphere secretions [31]. The fact is supported by [PERSON] et al. (2015) [32], who reported that fast-growing willow trees had the ability to stimulate indigenous bacteria in soil (_Actinomycetes_, _Burkholderiales_, and _Rhizobiales_) to produce cytochrome P450 monooxygenases and lactose/polphenol oxidases with the capability to degrade, for instance, fluoranthene, anthracene, and benzo[a]pyrene, in soil. Willow root exudates in the soil may cause the desorption of PAHs adsorbed on soil particles and enhance the use of PAHs by soil microorganisms [33,34]. When plants are under biotic or abiotic stress, they often secrete active metabolites and hormones from the root, which will cause positive plant-soil feedback [35, 36, 37]. _E.