*2.6. Statistical Analysis*

To determine the structure of the soil fauna in our study site, we chose density, the number of groups, and the Shannon-Wiener diversity index to describe the characteristics and composition of the soil fauna of each sample. The soil fauna density ( *D*) was calculated as the following:

$$D = \frac{N}{V};\tag{1}$$

where *D* is the density of soil fauna, *N* is the total number of individuals, and *V* is the volume of the soil samples. The number of groups ( *G*) was estimated as the number of groups of the fauna in the same order. The Shannon-Wiener diversity index ( *H*) of each sample was estimated according to Whittaker [56]:

$$H = -\sum\_{i=1}^{n} P\_i \ln P\_i \tag{2}$$

where *H* is the Shannon-Wiener diversity index of each sample, *n* is the number of groups of soil fauna, and *P*i is the proportion of the number of individuals in the *i*th order to the total number of individuals, which could be calculated with the following equation:

$$P\_{\mathbf{i}} = \frac{N\_{\mathbf{i}}}{N} \tag{3}$$

where *N*i is the number of individuals in the *i*th order.

Two-way ANOVA was used to examine the impact of N addition, soil layers, and their interactions on the fine root biomass (including live, dead, and total fine roots), density, number of groups, and biodiversity of phytophagous and total soil fauna. Repeated-measures ANOVA was performed to test the responses of litter mass, soil temperature, and moisture to N addition. One-way ANOVA was used to examine the responses of the litter C:N ratio, soil TN, and SOC to N addition. Linear regression analyses were performed to examine the relationships between soil fauna and fine root biomass (live, dead, and total), SOC, TN, mean annual soil temperature and between moisture and

the soil temperature in June. All statistical analyses were performed using SPSS 22.0 for Windows (SPSS Inc., Chicago, IL, USA).
