## 3 Results and Discussions
### Profiling of Functional Genes and Enzyme Activity during Biodegradation  
The real-time PCR quantification of functional soil bacteria involved in universal bacteria (_165 rRNA_), nitrogen fixation (_niffl_), ammoxidation (_amoA_), alkane degradation (_alkB_), and naphthalene degradation (_nah_) are shown in Figure 6.  
As shown in Figure 6, the diesel contamination in the soil led to a reduction for the universal bacteria (UB), the nitrogen-fixing bacteria (NFB), and the ammonia-oxidizing bacteria (AOB). By contrast, the amount of alkane degradation bacteria (ADB) and naphthalene degradation bacteria (NDB) increased. This indicated diesel contaminants harmful to UB, as described by [PERSON] et al. [51]. The amount of _alkB_ and _nah_ genes that encode, respectively, the alkane hydroxylase and naphthalene dioxygenase, are increased from 2 \(\times\) 104 to 1 \(\times\) 106, indicating the stimulation effect. Similar enrichments in indigenous degrading microorganisms by the selective pressure exerted by petroleum hydrocarbons have been reported [52; 53; 54]. There was a qualitative change of NDB, which was not detectable in the uncontaminated counterpart. The diesel contamination led to its appearance, up to 2 \(\times\) 105. The difference in the amount \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number** & **Component** & **Number** & **Component** & **Number** & **Component** \\ \hline
1 & C12H24 & 7 & C15H32 & 13 & C19H40 \\
2 & C7H5N & 8 & C14H3O & 14 & C20H42 \\
3 & C13H28 & 9 & C16H34 & 15 & C21H44 \\
4 & C12H24O & 10 & C15H32O & 16 & C22H46 \\
5 & C14H30 & 11 & C17H36 & 17 & C23H48 \\
6 & C7H12O2 & 12 & C18H38 & 18 & C24H50 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mass spectrometric analysis results of soil residual diesel components. Figure 5: Picture of the contaminated filed. of the ADB and NDB in the contaminated soil could be due to the different biodegradability for alkane and PAHs. The nitrogen cycle is one of the most important cycles in the biosphere, consisting of nitrogen assimilation, ammoniation, nitrogen fixation, nitrification, and denitrification. During the nitrogen cycle, the key reactions are catalyzed by dinitrogenase and ammonia oxidase, which are encoded by _nifH_, _amoA_ genes, respectively. The population of nitrogen cycle-related bacteria reflects nitrogen nutritional status in soil. The presence of NFB and AOB is also beneficial for the accumulation of available nitrogen. The decrease of NFB and AOB populations indicated the destruction of the nitrogen cycle due to diesel contamination, as [PERSON] and [PERSON] [55] reported. They found that light PAHs might cause the strong inhibition of the nitrogen cycle. As for the N-B process, the number of copies for all functional genes increased, indicating the promotion of both nitrogen cycle genes and degrading reactions. It was reported that biostimulation operations displayed high remediation efficiency when nutrient depletion occurred. Biostimulation could particularly effectively recover the nitrogen cycle [56]. The increase of the NDB displayed the effect of biostimulation as the gene level. Figure 5(b) analyzes the FDA hydrolase activity, dehydrogenase activity, urease activity, and phosphatase activity of the soil after restoration. First, the FDA hydrolase activity has recovered and exceeded the normal value, indicating that after the combined remediation of bioaugmentation and biostimulation, the pollutants in the soil are removed and the soil nutrient level is improved, thereby promoting the improvement of soil microbial activity. From the perspective of dehydrogenase, due to the addition of degrading bacteria, soil dehydrogenase activity is increased, laying a foundation for further bioremediation in the future. The activity levels of urease and phosphatase are more than in normal soil, showing that for the treatment of barren contaminated soil, biostimulation remediation technology can effectively restore the cyclic activity of soil nitrogen and phosphorus.