## 3 Results
### Changes of LFOM and HFOM  
The mass fractions of LFOC and LFON presented increasing trends, while the mass of LFOM decreased sharply. As a result, the contents of LFOC and LFON presented decreasing trends in all of the pots (Figure 3a,b). The reduction rates of LFOC and LFON in the experimental group were higher than those in the control group, and RSG presented the largest reduction. The elimination of biological residues and pellets before the experiment probably amputated the dominant sources of light fractions, which resulted in the degradation and reduction in the four pots. The HFOC contents were higher in the BS pots than in the RS pots, indicating that the carbon fractions were animate and largely affected by microbes in the rhizospheric environment (Figure 3c). Meanwhile, HFOC showed no remarkable difference during the process, which suggest that glucose degradation did not affect the HFOC mineralization. The HFON indicated a coincident and decreasing trend during the process, with high values in the control group, but low contents in the corresponding experimental group (Figure 3d). In addition, the LFOC was negatively related to pH, while HFOC and HFON were positively related to pH (\(\alpha<0.01\)), indicating that pH is probably an important factor affecting the degradation and formation of C or N fractions. Moreover, LFOC was positively associated with LFON, but negatively related to HFOC, suggesting that LFOC and HFOC may have internal conversion.  
Figure 2: (**a**) Changes of glucose (mg\(\cdot\)g\({}^{-1}\)), and (**b**) pH during the experiment in the four wetland pots.  
Furthermore, to analyze the carbon chain and functional group changes of LFOM during the experiment, the spectral properties in the wavelength of the 400 to 4000 cm\({}^{-1}\) regions of LFOM in the 8 th and 24 th hour were determined by Fourier-transform mid-infrared spectra. According to Lambert-Beer law, the mathematical expression is A = lg(1/T) (where A is the absorbance and T is the transmission ratio (transmittance)) [29]. The characteristic absorption peaks indicated the main chemical bonds and functional groups. The results showed that the spectral properties and shapes were very similar, and regular absorption peaks were mainly shown around 3150, 1646, 1400, 1038, 535, and 475 cm\({}^{-1}\) in the four pots (Figure 4a,b). The differences of peak intensity in LFOM between the 8 th h and 24 th h samples indicated the chemical bond changes during the glucose degradation. The pseudo-absorbance (PA) of LFOM had no significant differences among the pots and few changes during the process. The PA of LFOM in RSG was mostly lower than that in RS at all wavelengths except for 535 and 475 cm\({}^{-1}\). At the wavelength region above 1000 cm\({}^{-1}\), the PA at the 24 th h was higher than at the 8 th h of RSG, while the result was found at wavelengths below 1000 cm\({}^{-1}\) in the RS groups. For the BS and BSG pots, the PA in BS was higher than in BSG, especially at wavelengths below 1000 cm\({}^{-1}\). The PA in the 8 th h of BSG was higher than that at the 24 th h, but the reverse was true for BS.  
Figure 3: The changes of C and N fractions. Among which, (**a,b**) indicated the light fraction organic carbon (LFOC) and nitrogen (LFON), and (**c,d**) showed the heavy fraction organic carbon (HFOC) and nitrogen (HFON) in the wetland pots (mg\(\cdot\)g\({}^{-1}\)).