**5. Conclusions**

In this study, we linked species composition and leaf N:P stoichiometry along a slope aspect gradient. Our results reveal different types of nutrition limitation and species compositions in different slope aspects and highlight the functional significance of leaf N:P stoichiometry in community composition along a slope aspect gradient. We found that leaf N:P ratio was significantly lower on the NFS than on the SFS and WFS, although leaf [N] and [P] were not statistically different between slope aspects, implying N limitation and P limitation of plant growth on the NFS and SFS, respectively. Higher richness and coverage of forbs were found on the NFS than on the SFS, whereas those that of graminoids did not differ significantly between slope aspects. The variations in forb and graminoid richness were largely explained by leaf [N] and [P], respectively, with the possible mechanism of different N or P requirements for different PFGs. However, the mechanisms underlying the variations in leaf N:P stoichiometry and community composition across slope aspects are still not clear because we did not explore their correlations with environmental or soil factors.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/10.3390/d14040245/s1, Figure S1: Comparisons of leaf [N] (A,B), [P] (C,D), and N:P ratio (E,F) between sites and among slope aspects, respectively, for the species *Anaphalis lacteal*, Figure S2: Comparisons of leaf [N] (Panel A), [P] (Panel B), and N:P ratio (Panel C) between different plant functional groups (PFGs).

**Author Contributions:** Conceptualization, X.L.; methodology, R.Z.; software, X.L.; formal analysis, X.L.; investigation, X.L.; data curation, Y.H., X.Z. and C.Q.; writing—original draft preparation, X.L.; writing—review and editing, Y.H.; visualization, X.L.; supervision, X.L.; project administration, X.L. and R.Z.; funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the funding from Yangzhou University.

**Data Availability Statement:** The data presented in this study are available in article and Supplementary Materials.

**Acknowledgments:** We thank Zhao Jun, Song Xiaoyu, Nie Yingying, Chen Lingyun, and Zhang Jieqi for their help in the field and lab experiments. We thank Cui Xia for her help in working on Figure 1. This work was supported by the Research Station of Alpine Meadow and Wetland Ecosystems (RSAMWE) of Lanzhou University.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

