2.4 Statistical analyses
Three-way analysis of variance (ANOVA) was used to examine the effects of RFC, year of growth, plant species, and their interactions on fine root traits. Average root traits of entire soil profiles were used to calculate the percentage variation between rock-free soil and RFC treatments, as well as between the second year and other years. Thus, the variation range between RFC treatments and years of growth could be clearly indicated by points and lines. One-way ANOVA was used to determine significant differences inβ , biomass, length density, specific length, diameter, and tissue density of fine roots between RFC treatments. Data meeting the assumption of homogeneity of variance were tested by least significant difference (LSD); otherwise, data were analyzed using a non-parametric test (Kruskal-Wallis). The relationships between fine root traits and soil properties in the soil profile were tested using linear fitting. Principal component analysis was performed using the mean values of fine root traits on the entire soil profile and β to obtain an overview of the multidimensional root functions of different years of growth and species. We also performed redundancy analysis using fine root traits and soil properties in each soil layer of the second and third years along the RFC gradient. Data were analyzed using SPSS 25.0 (IBM, USA) for means and ANOVA. Theβ coefficient, line graph, and histogram were generated using the software Origin 2018 (OriginLab Corporation, USA). Principal component and redundancy analyses were implemented using the package “vegan” in R software (version 4.0.4; R Core Team, Austria).