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).