3.2 Influences of ECM traits on root and foliar N and P
The results of PCA on soil variables show that PC1 and PC2 respectively
explained 39.8% and 14.9% of the variations; the factors of high
scores include ACP, pH, TN, NO3--N,
TP, and SWC on PC1, and PR, C:Nsoil,
NH4+-N, and AP on PC2 (Table 2). For
the ECM traits, PC1 and PC2 respectively explained 40.4% and 17.8% of
the variations; factors of high scores include Cratio,
MDI, FRB, CE, SDE, SA, Root-tipsratio, and
ECMtips on PC1, and CE, MDE, and
Root-tipsratio on PC2 (Table 2).
Figure 3 illustrates the direct or indirect effects of explanatory
factors (soil variables, climatic factors, and ECM traits) on root and
foliar nutrient traits in SEMs (Figure 3). The root P concentration was
directly and significantly affected by MAT (δ = -0.48, SE = 0.12,P < 0.001), soil-PC1 (δ = -0.31, SE = 0.09, P< 0.001), soil-PC2 (δ = -0.33, SE = 0.09, P <
0.001), and ECM-PC1 (δ = 0.25, SE = 0.11, P < 0.05),
with an overall R2 value of 0.55 (CFI = 0.99, SRMR =
0.03; Figure 3a1). The root N concentration was directly and
significantly affected by soil-PC1 (δ = 0.31, SE = 0.09, P< 0.001), MAP (δ = -0.27, SE = 0.12, P <
0.05), MAT (δ = -0.56, SE = 0.12, P < 0.001), and
ECM-PC2 (δ =0.15, SE=0.09, P < 0.1), with an overall
R2 value of 0.52 (CFI = 0.99, SRMR = 0.03; Figure
3a2). The root N:P ratio was directly and significantly affected by
soil-PC1 (δ = 0.52, SE = 0.09, P < 0.01), soil-PC2 (δ =
0.18, SE = 0.09, P < 0.05), and ECM-PC2 (δ = 0.18, SE =
0.08, P < 0.1), with an overall R2value of 0.53 (CFI = 0.99, SRMR = 0.03; Figure 3a3).
The foliar P concentration was directly and significantly affected by
soil-PC1 (δ = -0.21, SE = 0.11, P < 0.1), soil-PC2 (δ
=-0.24, SE = 0.11, P < 0.05), MAP (δ = 0.44, SE = 0.14,P < 0.01), MAT (δ = -0.30, SE = 0.15, P< 0.05), and ECM-PC1 (δ = -0.26, SE = 0.14, P< 0.1), with an overall R2 value of 0.30
(CFI = 0.98, SRMR = 0.03; Figure 3b1). The foliar N concentration was
directly and significantly affected by MAP (δ = 0.28, SE = 0.14,P < 0.1), MAT (δ = -0.41, SE = 0.15, P< 0.01), and ECM-PC2 (δ = -0.21, SE = 0.11, P< 0.1), with an overall R2 value of 0.25
(CFI = 0.98, SRMR = 0.03; Figure 3b2). The foliar N:P ratio was directly
and significantly affected by soil-PC1 (δ = 0.44, SE = 0.11, P< 0.01), soil-PC2 (δ = 0.45, SE = 0.11, P <
0.01), MAP (δ = -0.41, SE = 0.13, P < 0.01), and
ECM-PC1 (δ = 0.25, SE = 0.13, P < 0.1), with an overall
R2 value of 0.37 (CFI=0.98, SRMR=0.03; Figure 3b3).
The soil and climatic factors also imposed indirect effects on root and
foliar nutrients by influencing ECM traits (Figure 3). While the ECM-PC1
significantly affected root and foliar P concentrations and foliar N:P
ratio, it was significantly affected by soil-PC1 (δ = -0.28, SE = 0.09,P < 0.01), soil-PC2 (δ = -0.29, SE = 0.01, P< 0.01), MAT (δ = -0.36, SE = 0.11, P <
0.01), and MAP (δ = 0.34, SE = 0.11, P < 0.01). MAT had
a significant effect on ECM-PC2 (δ = -0.40, SE =0.12, P< 0.05), which significantly affected root and foliar N
concentrations and root N:P ratio.
The RDA axis 1 (RDA1) and axis 2 (RDA2) respectively explained 38.7%
and 2.4% of the variations in root nutrient variables, and 25.5% and
1.23% of the variations in foliar nutrient variables (Figure 4). In
roots, there were significant positive relationships of P concentration
with Cratio and Root-tipsratio, between
N concentration and SA, and of the N:P ratio with FRB and MDI; both root
N and P concentrations were negatively related to the SDE, MDI, and FRB
(Figure 4a). In leaves, there were significant positive relationships
between P concentration and CE, of N concentration with
Cratio, Root-tipsratio, SA, and CE, and
of N:P ratio with FRB and MDI, respectively. While foliar N
concentration was negatively related to SDE, MDI, and FRB, the foliar P
was negatively to SDE, MDE MDI, and FRB (Figure 4b).