## 3 Results
The high-N and medium-N rates had statistically similar total microbial residues throughout the experiment; however, the medium-N treatment significantly stimulated total microbial residues in SOC by 3.38%, 7.35%, 11.94%, and 12.57% compared to the control in 2015, 2016, 2017, and 2018, respectively. The ratio of fungal residues to bacterial residues in SOC significantly varied by nitrogen enrichment from 2016 to 2018 and decreased with an increase in N rate (Figure 2d). The ratio of fungal residues to bacterial residues ranged from 3.40 to 3.74 and decreased over time. The ratio decreased by 6.25% in 2016, 6.28% in 2017, and 6.85% in 2018 under the high-N treatment compared to the control. Effects of Chronic Nitrogen Enrichment on Microbial Biomass, and Dissolved Organic Carbon and Nitrogen Concentrations in the Soil from 2014 to 2018  
Nitrogen enrichment significantly affected microbial biomass (MBN and MBC) from 2015 to 2018 (Figure 3a,b). The MBN concentration in the soil ranged from 5.66 to 13.1 mg kg\({}^{-1}\), while the MBC concentration ranged from 79.36 to 117.11 mg kg\({}^{-1}\). Microbial biomass followed a linear trend and increased with increasing N rate; however, the high-N and medium-N treatments had statistically similar microbial biomass throughout the study period. Compared to the control, the medium-N treatment stimulated MBN by 28.63%, 38.17%, 45.98%, and 47.86% in 2015, 2016, 2017, and 2018, respectively. Similarly, the MBC content increased under the medium-N treatment by 7.59% in 2015, 15.30% in 2016, 20.56% in 2017, and 23.58% in 2018 compared to the control. Similar to microbial biomass, the ratio of MBC to SOC varied significantly by N enrichment from 2014 to  
Figure 2: Effects of nitrogen enrichment on bacterial residues in SOC (**a**), fungal residues in SOC (**b**), total microbial residues in SOC (**c**), and ratio of fungal residues to bacterial residues in SOC (**d**). Bars represent \(\pm\) standard error of means with four replications. 2018 (Figure 3c). The MBC/SOC ratio ranged from 9.18 to 12.19 and ranked as: high-N > medium-N > low-N > no-N, throughout the experiment. The effect of N enrichment on the MBC/MBN ratio was also significant from 2014 to 2018 and decreased over time (Figure 3d). The ratio of MBC to MBN ranged from 8.59 to 14.47, and it decreased with increasing N rate and followed this trend: no-N > low-N > medium-N > high-N, respectively, throughout the study. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were significantly stimulated by N enrichment and increased from 2015 to 2018 (Figure 4a,b). The DOC and DON contents followed a linear trend and ranged from 179.3 to 266.0 mg kg\({}^{-1}\) and 129.5 to 223.8 mg kg\({}^{-1}\), respectively. Similar to MBC and MBN, DOC and DON increased with an increasing N application rate. The DOC and DON contents were ranked as: high-N > medium-N > low-N > no-N, throughout the study period. Similar to the MBC/SOC ratio, the ratio of dissolved organic carbon to soil organic carbon (DOC/SOC) varied significantly from 2016 to 2018 by nitrogen enrichment (Figure 4c). All treatments increased the DOC/SOC ratio over time; however, it increased with an increase in N rate. The DOC/SOC ratio ranged from 20.78 to 27.68. The high-N and medium-N treatments had statistically similar ratio throughout the experimental period; however, the DOC/SOC ratio was stimulated by 6.60% in 2016, 9.12% in 2017, and 11.07% in 2018 under the medium-N treatment compared to the control. The ratio of dissolved organic carbon to dissolved organic nitrogen (DOC/DON) was significantly affected by nitrogen enrichment and decreased with increasing N rate (Figure 4d). The DOC/DON ratio ranged from 1.09 to 1.45 and decreased over time. The DOC/DON ratio was ranked as: no-N > low-N > medium-N > high-N, respectively. Soil organic carbon was significantly affected by nitrogen enrichment from 2016 to 2018 (Table 2).