*3.1. Mycorrhizal Colonization*

No colonization was observed in the NM treatments. However, in AM treatments, mycorrhizal colonization of the three plant species varied within the same treatment; specifically, the colonization of *S. viridis* and *L. chinensis* was significantly greater than that of *S. corniculata* (*p* < 0.05) except in the treatment with warming and N input combined (Table 1).

**Table 1.** The colonization status (%) of arbuscular mycorrhizal fungi (AMF) treatment under warming (W) and N input (N). CK, control; N, N input; W, warming; W × N, combination of warming and N input.


Note: The colonization status with different superscripts (a or b) differ significantly at *p* = 0.05 among different plant species in the same treatment.

### *3.2. Plant Nutrients and Stoichiometric Ratios*

Three-way factorial analyses of variance revealed significant main effects of warming on the C, N, and P contents and stoichiometric ratios of the three plant species except for C and P contents in *S. corniculata* and the C:P ratio in *S. viridis* and *S. corniculata*. Significant main effects of N input on the C, N, and P contents of *S. corniculata*; the N content of *S. viridis*; the C:N and N:P ratios of all three species; and the C:P ratio of *L. chinensis* were detected. Significant interaction effects of W × N on the C, N, and P contents of *S. viridis*; the C:N ratio of *L. chinensis*; the C:P ratios of S. viridis and *L. chinensis*; and the N:P ratios of *L. chinensis* and *S. corniculata* were observed (Table 2).

**Table 2.** Results of three-way factorial analyses of variance (ANOVAs) of the effects of warming, N input and arbuscular mycorrhizal fungi (AMF) on plant C, N, and P contents and ratios of C:N, C:P, and N:P.



**Table 2.** *Cont.*

\* represents a significant difference at *p* < 0.05; \*\* represents a significant difference at *p* < 0.01; \*\*\* represents a significant difference at *p* < 0.001.

AMF increased the C content of *S. viridis* by 119% and 138% (*p* < 0.05; Figure 1A) in the N and WN treatments, respectively, and increased the C content of *L. chinensis* by 282% ( *P* < 0.01; Figure 1B) in the N treatment. There were significant effects of AMF × N and AMF × W on C content in *S. viridis* and *L. chinensis*, respectively (Table 2), whereas C contents in *S. corniculata* and N content in *S. viridis* were not affected by AMF (Figure 1C,D; Table 2).

AMF increased the N content of *L. chinensis* by 231% (*p* < 0.01; Figure 1E) in the N treatments and decreased the N content of *S. corniculata* by 52% (*p* < 0.001, Figure 1F) in the WN treatments. There were significant effects of AMF ×W and AMF × N on N content in *L. chinensis* and *S. corniculata*, respectively (Table 2).

AMF increased the P content of *S. viridis* by 54%, 118% (*p* < 0.05), and 115% (*p* < 0.05, Figure 1G) in the W, N, and WN treatments, respectively, and by 299% (*p* < 0.01; Figure 1H) in the *L. chinensis* in the N treatment but decreased the P content in *S. corniculata* by 42% (*p* < 0.05, Figure 1I) in the WN. AMF × W and AMF × W × N had significant effects on the P content in *L. chinensis* and *S. corniculata*, respectively (Table 2).

**Figure 1.** Effects of AMF on the C, N, and P contents of *S. viridis* (**A**,**D**,**G**), *L. chinensis* (**B**,**E**,**H**), and *S. corniculata* (**C**,**F**,**I**) under warming and N input. Different lowercase and capital letters above bars indicate significant differences (*p* < 0.05) among different warming and N input treatments within the same AMF treatment. Asterisks indicate significant differences (*p* < 0.05) between AMF treatments within the same warming and/or N input condition. CK, control; N, N input; W, warming; and WN, combination of warming and N input.

AMF increased the C:N ratio of *S. viridis* by 74% (*p* < 0.01), 57% (*p* < 0.05), 122% (*p* < 0.001), and 121% (*p* < 0.01; Figure 2A) in the control, warming, N input and combination of warming and N input, respectively. AMF decreased the C:N ratio of *L. chinensis* by 36% (*p* < 0.001) in the CK treatment, but in the N and WN treatments, AMF increased the C:N ratio of *L. chinensis* by 17% (*p* < 0.01) and 48% (*p* < 0.001; Figure 2B), respectively. There were significant effects of AMF × W and AMF × N on the C:N ratio of *L. chinensis* (Table 2). AMF significantly increased the C:N ratio of *S. corniculata* by 114% (*p* < 0.001) and 25% (*p* < 0.01; Figure 2C) in the N and WN treatments, respectively.

AMF increased the C:P ratio of *S. viridis* by 11% (*p* < 0.05; Figure 2D) in the WN treatment and that of *S. corniculata* by 18% (*p* < 0.05; Figure 2F) in the CK treatment; it had no impact in the other treatments. There were significant effects of AMF × N on the C:P ratios of *S. viridis* and *L. chinensis* and of AMF × W and AMF × W × N on the C:P ratio of *S. corniculata* (Table 2).

AMF decreased the N:P ratio of *S. viridis* by 51%, 48% (*p* < 0.01), 51% (*p* < 0.001), and 52% (*p* < 0.01; Figure 2G) in the in the control, warming, N input and combination of warming and N input, respectively. AMF increased the N:P ratio of *L. chinensis* by 46% (*p* < 0.01) in the CK treatment but decreased that of *L. chinensis* by 16% (*p* < 0.05) and 27% (*p* < 0.01; Figure 2H) in the N and WN treatments, respectively. AMF decreased the N:P ratio of *S. corniculata* by 49% (*p* < 0.001) and 15% (*p* < 0.05; Figure 2I) in the N and WN treatments, respectively. There were significant effects of AMF × N on the N:P ratio of all three species and of AMF × W and AMF × W × N on the N:P ratio of *L. chinensis* and *S. corniculata* (Table 2).

**Figure 2.** Effects of AMF on the C:N, C:P, and N:P ratios of *S. viridis* (**A**,**D**,**G**, *L. chinensis* (**B**,**E**,**H**) and *S. corniculata* (**C**,**F**,**I**) under warming and N input. Different lowercase and capital letters above bars indicate significant differences (*p* < 0.05) among different warming and N input treatments within the same AMF treatment. Asterisks indicate significant differences (*p* < 0.05) between AMF treatments within the same warming and/or N input condition. CK, control; N, N input; W, warming; and WN, combination of warming and N input.

### *3.3. Soil Nutrients and Stoichiometric Ratios*

Three-way factorial analyses of variance showed significant differences on the effects of warming on soil N and P contents and the C:N ratio; of N input on soil N and P contents and the C:N, C:P and N:P ratios; and of W × N on the C:P ratio (Table 3).

**Table 3.** Results of three-way factorial analyses of variance (ANOVAs) of the effects of warming, N input and arbuscular mycorrhizal fungi (AMF) on soil total C, N, and P contents and ratios of C:N, C:P, and N:P.


\* represents a significant difference at *p* < 0.05; \*\* represents a significant difference at *p* < 0.01; \*\*\* represents a significant difference at *p* < 0.001.

AMF had no effects on soil nutrients and stoichiometric ratios (Table 3); however, under N input, the soil N content and the N:P ratio were reduced by 18% (*p* < 0.05) and 29% (*p* < 0.05; Figure 3B,F), respectively, and the soil C:N ratio was increased by 22% (*p* < 0.05; Figure 3D) in the presence of AMF. In the WN treatment, AMF decreased the soil P content by 22% (*p* < 0.05; Figure 3C) and increased the soil N:P ratio by 44% (*p* < 0.05; Figure 3F). Significant effects of W × AMF on soil N and P contents and the C:N, C:P and N:P ratios; of N × AMF on soil P content and the C:P and N:P ratios; and of W × N × AMF on the soil N:P ratio were observed (Table 3).

**Figure 3.** Effects of AMF on soil C ( **A**), N (**B**), and P ( **C**) contents and C:N ( **D**), C:P (**E**), and N:P (**F**) ratios under warming and N input. Different lowercase and capital letters above bars indicate significant differences (*p* < 0.05) among different warming and N input treatments within the same AMF treatment. Asterisks indicate significant differences (*p* < 0.05) between AMF treatments within the same warming and/or N input condition. CK, control; N, N input; and W, warming; WN, combination of warming and N input.
