## 3 Results and Discussions  
### The Microbial and Gene Kinetics of Different Degradation Approaches  
The degradation using natural volatilization (S), natural attenuation (C), biostimulation (N), bioaugmentation (B), and the biostimulation-bioaugmentation (N-B) joint process was conducted, as described in the previous portion. The residual diesel content changes in each experiment system were thus plotted and shown in Figure 2. The _alkB_ and _nah_ genes, which encode the degradation activities for alkene and aromatic compounds, and the _nifH_ and _amoA_ gene encoding nitrogen cycle, are also shown in Figure 2. The kinetic picture of bioremediation of diesel degradation was obtained, from which the different degradation performance by different remediation processes were identified.  
It can be seen in Figure 2a that the residual content of diesel was down to 1.09% in the case of the biostimulation-bioaugmentation joint process. The volatilization contributes to a reduction of diesel content within 0.1-0.3%, indicating the necessity of implementing bioremediation procedures. Both B and N-B processes showed a lag phase of 3 days, indicating the growth of the inoculated degrading bacteria. As for the N process, the lag phase extended to 12 days. Here the N-B system removed 58% of diesel, exhibiting the highest degrading efficiency.  
Figure 2b shows the variation of the number of the total bacteria during the degradation in the soil. Here we ignored system S because it was subjected to sterilization treatment before bioremediation. The amount of the 16S rRNA gene copies maintained a low level in the C system, which, we believe, reflected the toxic effects of diesel that hindered microbial proliferation. As for other systems, the amount of the total bacteria increased from \(10^{7}\) to about \(10^{11}\), in which the N-B system appeared the highest bacterial growth. An increase in microbial 16S rRNA also appears for the B and N systems, respectively, indicating the colonization of the exogenous bacteria and the effect of biostimulation.  
Figure 2c,d give the changes in amount of the _alkB_ and _nah_ gene copies. The amount of _alkB_ gene copies increased from \(10^{6}\) to \(10^{10}\) in the B system, which could be attributed to the inoculation of the degrading strain. We also observe the increase of _nah_ gene copies, which does not exist in _Pseudomonas_ sp. Therefore, the magnificent increase of the _nah_ gene was attributed to the increase of microorganisms in the soil caused by biostimulation.  
Figure 2e,f give the recovery of the nitrogen cycle genes in different experimental systems. Here B and C both show a low effect on promoting the _nifH_ and _aomA_ genes, which indicated that exogenous bacteria might mostly act on the degradation reaction. By contrast, N showed the best effect for increasing the nitrogen cycle genes; for instance, the _nifH_ gene copies amount increased from \(10^{5}\) to \(10^{9}\). Here the variation of _nifH_ and _aomA_  
Figure 1: Schematic diagram of contaminated site.  
genes before and after the remediation confirmed the effectiveness of the biostimulation in the restoration of the soil nitrogen cycle.