Fig. 7
Structural equation model of NO3− and pH effects on aboveground tree growth rate and root morphologies. A Structural equation model of Q. acutissima (χ2 = 12.033; df = 10, p = 0.283 > 0.05; GFI = 0.951 > 0.900; RMSEA = 0.068 < 0.080). B Structural equation model of C. lanceolata (χ2 = 12.627; df = 11, p = 0.318 > 0.05; GFI = 0.951 > 0.900; RMSEA = 0.058 < 0.080). Numbers on lines are standardized path coefficients. The widths of lines indicate the strength of the causal influence. Solid lines represent the direct effects on plant growth rates and root growth, dotted lines represent the effects on root physiologies. pH, AR pH; NO3−, the concentration of NO3− in AR; HGR, height growth rate; DGR, basal diameter growth rate; TRL, total root length; TRS, total root surface area; TTC, root activity; SOD, activity of superoxide dismutase in root; POD, activity of peroxidase in root; CAT, activity of catalase in root