**5. Conclusions**

Both the input and the output of litter and litter carbon in the subalpine forest streams showed similar patterns with critical periods, as affected by seasonal changes in temperature and precipitation together with stream characteristics (length, flow velocity, sediment depth, etc.). The seasonal temperature pattern and the stream length dominated the input of litter and litter carbon to the stream. Meanwhile, the seasonal temperature and precipitation patterns, sediment depth, and flow velocity determined the output of litter and litter carbon from the stream. Additionally, the litter and litter carbon input to the streams were higher than the output from the streams in the forest stream ecosystem, indicating that the subalpine forest streams play a crucial role in linking the carbon biogeochemical cycle between subalpine forests and downstream rivers. In-depth investigations on the carbon biogeochemical linkages in forest–riparian–river meta-ecosystems should be conducted, particularly concerning the linkages between the carbon biogeochemical cycle in the metaecosystems and forest characteristics, topographical features, and catchment shapes under different climate change scenarios.

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

**Funding:** This study was supported by the National Natural Science Foundation of China (32071554, 32001139).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data generated or analyzed during this study are included in this published article. No new data were created or analyzed in this study. Data sharing is not applicable to this article. Data in Table 4 are available through Triska et al. 1982, Benfield 1997, Webster et al. 1997, Hart 2006, Muto 2008, Tonin et al. 2017, and Railoun 2018.

**Acknowledgments:** The authors of this study would like to thank all people involved in the initial sampling assignments.

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