**3. Results**

#### *3.1. Carbon, Nitrogen, and Phosphorus Contents in Mature and Senescent Leaves*

The contents of C, N, and P in mature and senescent leaves mostly differed significantly between plantations and varied with months (Figure 2). The C content in the mature leaves of the *Cunninghamia lanceolata* plantation was lower in April and May than of the *Castanopsis carlesii* plantation, but higher at subsequent times (Figure 2a). During the growing season, the N content in both mature and senescent leaves of the *Cunninghamia lanceolata* plantation was significantly lower than that of the *Castanopsis carlesii* plantation (Figure 2c,d). The P content in mature leaves of the *Cunninghamia lanceolata* plantation was significantly higher than that of the *Castanopsis carlesii* plantation in May and September, and this pattern was more pronounced in senescent leaves (Figure 2e,f).

**Figure 2.** C, N and P contents in mature (**<sup>a</sup>**,**c**,**<sup>e</sup>**) and senescent leaves (**b**,**d**,**f**). Each scatter represents the average value of the three replicates (*n* = 3). Error bars represent standard errors (SE). The *p* values show the results from repeated measures ANOVA testing for the effect of forest type over time. *ns*: not significant. Asterisks denote significant differences between forest types: \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001.

Leaf N and P contents in both plantations decreased markedly during leaf senescence, and the dynamical patterns of decrease differed significantly between plantations (Figure 3). The N content decreased significantly more in the *Cunninghamia lanceolata* plantation than in the *Castanopsis carlesii* plantation in May, while it was significantly less than in the *Castanopsis carlesii* plantation in July (Figure 3a). In contrast, the P content decreased significantly more in the *Cunninghamia lanceolata* plantation than in the *Castanopsis carlesii* plantation in April and September, while it was significantly less than in the *Castanopsis carlesii* plantation in June, July, and October (Figure 3b).

**Figure 3.** Changes in N (**a**) and P contents (**b**) during leaf senescence. Each column represents the average value of the three replicates (*n* = 3). Error bars represent standard errors (SE). The *p* values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001.

#### *3.2. Nitrogen and Phosphorus Resorption Efficiencies in the Leaves of Castanopsis carlesii and Cunninghamia lanceolata Plantations*

Dynamical patterns of N and P resorption efficiencies differed significantly between plantations (Figure 4). The N resorption efficiencies of the *Cunninghamia lanceolata* plantation and the *Castanopsis carlesii* plantation varied from 34.26% to 56.28% and from 11.25% to 34.23%, respectively (Figure 4a). The N resorption efficiency of the *Cunninghamia lanceolata* plantation was significantly lower than that of the *Castanopsis carlesii* plantation in July but higher in most months. In contrast, the P resorption efficiencies of the *Cunninghamia lanceolata* plantation and the *Castanopsis carlesii* plantation varied from 41.01% to 54.85% and from 49.22% to 58.72%, respectively (Figure 4b). The P resorption efficiency of the *Cunninghamia lanceolata* plantation was significantly lower than that of the *Castanopsis carlesii* plantation in most sampling months.

*Castanopsis carlesii* plantation *Cunninghamia lanceolata* plantation

**Figure 4.** Leaf N (**a**) and P (**b**) resorption efficiencies. *NRE*: Nitrogen resorption efficiency, *PRE*: Phosphorus resorption efficiency. Each column represents the average value of the three replicates (*n* = 3). Error bars represent standard errors (SE). The *p* values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: \* *p* < 0.05, \*\* *p* < 0.01. The dotted line represents the 50% threshold.

#### *3.3. Carbon, Nitrogen, and Phosphorus Stoichiometric Ratios in Mature and Senescent Leaves*

The C:N, C:P, and N:P ratios in mature leaves varied from 31.39 to 61.24, from 753.09 to 1022.54, and from 14.57 to 28.92 during the investigation period, respectively (Figure 5). Forest types displayed a significant effect on C:N in mature leaves (Figure 5a). The C:N of mature leaves in the *Cunninghamia lanceolata* plantation was significantly higher than that of the *Castanopsis carlesii* plantation in all months. The C:P of mature leaves varied with time, and the variation patterns varied significantly between plantations (Figure 5c). The C:P of mature leaves in the *Cunninghamia lanceolata* plantation was significantly lower than that in the *Castanopsis carlesii* plantation in May and September, but higher in October. The N:P of mature leaves also differed significantly between plantations (Figure 5e). Compared to the *Castanopsis carlesii* plantation, the *Cunninghamia lanceolata* plantation had significantly lower mature leaf N:P.

**Figure 5.** C:N, C:P, and N:P ratios in mature (**<sup>a</sup>**,**c**,**<sup>e</sup>**) and senescent leaves (**b**,**d**,**f**). Each scatter represents the average value of the three replicates (*n* = 3). Error bars represent standard errors (SE). The *p* values show the results from repeated measures ANOVA testing for the effect of forest type over time. *ns*: not significant. Asterisks denote significant differences between forest types: \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001.

The C:N, C:P, and N:P of senescent leaves varied from 34.45 to 110.42, from 1292.61 to 2060.64, and from 14.50 to 49.94, respectively. Forest types exhibited a significant effect on the C:N:P stoichiometric ratios in senescent leaves (Figure 5). The C:N of senescent leaves in the *Cunninghamia lanceolata* plantation was significantly higher than that of the *Castanopsis carlesii* plantation in all sampling months (Figure 5b). In contrast, C:P and N:P in senescent leaves of the *Cunninghamia lanceolata* plantation were significantly lower than that of the *Castanopsis carlesii* plantation (Figure 5d,f).

#### *3.4. Correlation of Nutrient Contents, Resorption Efficiencies, and Stoichiometric Ratios with Climatic Factors*

In the *Castanopsis carlesii* plantation, the temperature was significantly negatively correlated with senescent leaf P content and significantly positively correlated with leaf

*PRE* (Figure 6). Precipitation was significantly negatively correlated with leaf *NRE*, *PRE*, mature leaf N and P contents, and senescent leaf C:N and significantly positively correlated with senescent leaf N, mature leaf C:N, and C:P. In the *Cunninghamia lanceolata* plantation, the temperature was significantly negatively correlated with leaf *NRE*, *PRE*, senescent leaf C:N, and C:P, and significantly positively correlated with senescent leaf N content (Figure 7). Precipitation was significantly positively correlated with senescent leaf P content.

**Figure 6.** Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the *Castanopsis carlesii* plantation. *NRE*: N resorption efficiency; *PRE*: P resorption efficiency; *Cm*: C content in mature leaves; *Nm*: N content in mature leaves; *Pm*: P content in mature leaves; *Cs*: C content in senescent leaves; *Ns*: N content in senescent leaves; *Ps*: P content in senescent leaves. *C:Nm*: C:N in mature leaves; *C:Pm*: C:P in mature leaves; *N:Pm*: N:P in mature leaves; *C:Ns*: C:N in senescent leaves; *C:Ps*: C:P in senescent leaves; *N:Ps*: N:P in senescent leaves. *T*: Temperature; *P*: Precipitation. Asterisks indicate significant correlations among indicators. \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001. The same is below.

**Figure 7.** Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the *Cunninghamia lanceolata* plantation. Asterisks indicate significant correlations among indicators. \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001.
