2.5 Statistical analysis
One-way analysis of variance (ANOVA) was used to analyze species richness, total coverage, the importance value (IV) of shared species, and the IV of unique species between infected sites and non-infected sites. The data were checked for normality and the significance level was 0.05. The linear or nonlinear relationships were analyzed based on a regression analysis between the soil nutrient and leaf nutrient (C, N, P, K) concentrations and SW and leaf nutrient concentrations (N, P, N:P, N:K, and P:K ratio). The above statistical analyses were carried out using SPSS 21 (PASW statistics 21.0; IBM Corporation, Armonk, NY, USA) and the graphs were constructed using SigmaPlot 12.5 (SyStat Software Inc., San Jose, CA, USA). The variation in leaf N, P, and the N:P ratio was partitioned between two explanatory variable groups (soil water content and soil nutrient content) using a partial regression analysis (PCA) with a redundancy analysis (RDA) (Chen et al., 2016). The PCA and RDA were carried out using CANOCO 5.0 (Microcomputer Power, Ithaca, NY, USA).
The response ratios (RR) for invasion by P. kansuensis were calculated according to Hedges et al. (1999):
RR = ln(Xt / Xc )
where Xt represents the soil nutrient value for the P. kansuensis infected sites and Xc is the soil nutrient value for the control group (non-infected sites).
Results