**3. Results**

### *3.1. Variation in Leaf Stoichiometry among C. paliurus Populations*

Significant differences were found in leaf N and P concentrations and N:P ratios among different populations of *C. paliurus* (Table 1). For the 30 populations studied, the mean values of N and P concentrations and N:P ratios were 9.57 mg g<sup>−</sup>1, 0.91 mg g<sup>−</sup><sup>1</sup> and 10.51, respectively, with a range of 5.89 (Wencheng, Zhejiang)–15.18 (Qingchuan, Sichuan) mg g<sup>−</sup>1, 0.50 (Wencheng, Zhejiang)–1.18 (Jingde, Anhui) mg g<sup>−</sup>1, and 7.04 (Jinggangshan, Jiangxi)–18.39 (Laowangshan, Zhejiang) (Table 1), respectively. Moreover, leaf N concentrations were significantly correlated with leaf P concentrations (*R*<sup>2</sup> = 0.1815, *p* = 0.0189) (Figure 2).

**Figure 2.** The relationship between leaf N and P concentrations for the 30 *C. paliurus* populations.

### *3.2. Soil Properties and Their Relationships with Leaf Stoichiometry*

Soil organic C, total N and total P concentrations varied significantly among the natural populations, ranging from 24.04 (Jianhe, Hunan) to 75.82 (Leigongshan, Guizhou) mg g<sup>−</sup>1, 1.94 (Yongshun, Hunan) to 5.84 (Leigongshan, Guizhou) mg g<sup>−</sup>1, and 0.76 (Baise, Guangxi) to 3.52

(Shangcheng, Henan) mg g<sup>−</sup><sup>1</sup> (Table 2), respectively. Table 3 shows that there were no significant correlations between leaf stoichiometry and the soil properties studied (including soil C, N and P concentrations).


**Table 2.** Soil organic C, total N and total P concentrations for the 30 *C. paliurus* populations.

Note: QLF sample missing (sm). Sample ID was defined from the abbreviation of the location name. Different letters indicate significant differences (*p* <0.05 by Tukey's test) between populations.



### *3.3. Leaf Stoichiometry in Relation to Geographic and Climate Variables*

Leaf stoichiometry of *C. paliurus populations* was significantly related to both geographic and climate variables of their origins. Leaf N concentration was positively correlated with latitude (*R*<sup>2</sup> = 0.2747 and *p* = 0.0030 for the linear fit) (Figure 3A), but negatively correlated with mean annual temperature (MAT) (*R*<sup>2</sup> = 0.2130 and *p* = 0.0103 for the linear fit) (Figure 4A), mean temperature in January (MTmin) (*R*<sup>2</sup> = 0.3077 and *p* = 0.0015 for the linear fit) (Figure 4C), and mean annual frost-free period (MAF) (*R*<sup>2</sup> = 0.2319 and *p* = 0.0071 for the linear fit) (Figure 5B). Leaf P concentration was negatively related to longitude (*R*<sup>2</sup> = 0.1660 and *p* = 0.0255 for the linear fit) (Figure 3E). Leaf N:P ratios were positively correlated with latitude (*R*<sup>2</sup> = 0.2921 and *p* = 0.0020 for linear fit) (Figure 3G), mean temperature in January (MTmin) (*R*<sup>2</sup> = 0.1741 and *p* = 0.0218 for the linear fit) (Figure 4I), and mean annual frost-free period (MAF) (*R*<sup>2</sup> = 0.1655 and *p* = 0.0257 for the linear fit) (Figure 5F).

**Figure 3.** Relationships between leaf N (**A**–**C**), P (**D**–**F**), N:P ratio (**G**–**I**) and geographic origin (latitude, longitude and altitude) of *C. paliurus* populations.

**Figure 4.** Relationships between leaf N (**A**–**C**), P (**D**–**F**), N:P ratio (**G**–**I**) and temperature (MAT: mean annual temperature, MTmax: mean temperature in July, and MTmin: mean temperature in January) for *C. paliurus* populations.

**Figure 5.** Relationships between leaf N (**A**,**B**), P (**C**,**D**), N:P ratio (**E**,**F**) and mean annual precipitation (MAP), and mean annual frost-free period (MAF) of *C. paliurus* populations.
