**5. Conclusions**

This paper presents, to the best of our knowledge, the first field evidence to elucidate how different species integrated over different life stages cope with synthetic environmental changes (altitude) from the perspective of carbon and nutrient allocation strategies. Our results demonstrate that both deciduous and evergreen trees in their early life stage perform similarly compared to their adult individuals along an environmental gradient (from the timberline to the alpine treeline). Our results indicate that most of our knowledge of forest responses, especially shoot and root responses, to global environmental changes gained from experiments with seedlings/saplings growing in artificially controlled conditions could, to some extent, upscale to larger and mature trees growing in situ. This finding advances our understanding of plants' adaptation strategies and has considerable implications for future model-developments.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1999-4907/10/5/394/s1. Table S1: Description of sampling transects and plots for *Pinus cembra* L. and *Larix decidua* Mill. in the South Swiss Alps, Table S2: LMM results for the effects of species (*Pinus cembra* L. and *Larix decidua* Mill.), altitude (timberline and treeline), tree age (sapling and adult tree), sampled season (mid-growing season: August; and late-season: October) on NSCs, nutrients, and stable isotope over tissues. The interactions were retained in the models only when significant. *df*: degrees of freedom. Significant *p*-values are in bold face, Table S3: LMM results for the effects of species (*Pinus cembra* L. and *Larix decidua* Mill.), altitude (timberline and treeline), tree age (sapling and adult tree), sampled season (mid-growing season: August; and late-season: October) on the stoichiometric ratios (C:N and N:P). The interactions were retained in the models only when significant. *df*: degrees of freedom. Significant p-values are in bold face, Table S4: LMM results for the effects of altitude (timberline and treeline), tree age (sapling and adult tree), sampled season (mid-growing season: August; and late-season: October) and their interactions on NSCs, nutrients and stable isotope over tissues of *Pinus cembra* L. The interactions were retained in the models only when significant. *df*: degrees of freedom. Significant p-values are in bold face, Table S5: LMM results for the effects of altitude (timberline and treeline), tree age (sapling and adult tree), sampled season (mid-growing season: August; and late-season: October) and their interactions on NSCs, nutrients and stable isotope over tissues of *Larix decidua* Mill. The interactions were retained in the models only when significant. *df*: degrees of freedom. Significant *p*-values are in bold face.

**Author Contributions:** Conceptualization, M.-H.L., J.-F.L., W.-F.X., and Z.-P.J.; methodology, M.-H.L., J.-F.L., W.-F.X., and Z.-P.J.; formal analysis, J.-F.L. and Y.-Y.N.; investigation, J.-F.L. and M.-H.L.; writing—Original draft preparation, J.-F.L.; writing—Review and editing, M.-H.L., M.S., and A.G.; supervision, M.-H.L., J.-F.L., W.-F.X., Z.-P.J., M.S., and A.G.

**Funding:** This research was funded by the Fundamental Research Funds for the Central Non-Profit Research Institution of CAF (CAFYBB2014ZD001), the National Natural Science Foundation of China (No. 41371076 and 41371075), and the China Scholarship Council (No. 201303270003).

**Acknowledgments:** The authors are grateful for the laboratory assistance from Ursula Graf (WSL).

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

#### **References**


© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
