3.4 Analysis of fungal community structure
A total of 491602 high-quality fungal ITS gene sequences generated from the lawn soil samples were clustered into 2698 OTUs at 97% sequence similarity. The dominant fungal phyla across lawn soil samples were Ascomycota (21.1–36.6%), Basidiomycota (6.7–10.1%), and Mucoromycota (0.7–5.4%). The highest relative abundance of Ascomycota was found in the N225 treatment, while the lowest was found in the N150 treatment. In contrast, the relative abundance of Basidiomycota was the highest in the N150 treatment, and the lowest in the N300 treatment. The highest relative abundance of Mucoromycota was found in the N300 treatment and the lowest was found in the N225 treatment (Fig. 4a). N fertilizer significantly increased the relative abundance ofAscomycota , yet significantly decreased the relative abundance of Basidiomycota.
The top three dominant fungi belonged to the generaPyrenochaetopsis (2.1–10.8%), Chaetomium (1.0%–7.0%), and Mortierella (0.7–4.3%). Specifically, the relative abundance of Pyrenochaetopsis in the N225 treatment (10.81%) was significantly higher than that in the other three treatments (P < 0.05) (Fig. 4b). N fertilizer significantly increased the relative abundance of Pyrenochaetopsis , Penicillium ,Talaromyces , Humicola , Guehomyces , andThermomyces , while significantly decreased the relative abundance of Chaetomium, Mortierella , Tuber , and Simplium .
The fungal community structure was used as a variable, and PCA was performed in 12 treatment plots. The axis PC1 and PC2 explained 85.44% of the variation information of the fungal community structure. According to the analysis, except for the control plot, the 9 plots treated with N150, N225, and N300 had obvious distribution areas on PC1 and PC2 and were distributed centrally for the same treatment (Fig. 5). This indicated that the fungal community structure was altered by N fertilizer.