**5. Conclusions**

*Petasites japonicus* subsp. *giganteus* had a high capacity for acclimation to different light environments. In this species, having lower LMA associated with a lower photosynthetic rate in the understory did not increase net daily photosynthesis on the sunny day due to frequent sunflecks, but instead reduced construction costs per unit leaf area. These results indicate that when sunflecks were present, information on static leaf photosynthetic traits may not be sufficient to evaluate shade acclimation in forest understories.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1999-4907/11/12/1365/s1. Supplementary Materials: data and PPFD\_and\_P\_net.

**Author Contributions:** Conceptualization, K.K.; methodology, K.K.; formal analysis, K.K.; investigation, R.D. and K.K.; writing—original draft preparation, R.D. and K.K; writing—review and editing, K.K.; supervision, K.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the Japan Society for the Promotion of Science (KAKENHI Grant Number 18K06406).

**Acknowledgments:** We thank Yasuyo Nagase and Miro Harada for performing preliminary studies. We thank staff members of Obihiro City Office and Obihiro Forest Hagukumu for permitting us to perform the fieldwork at the study sites.

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

**Data Availability Statement:** The datasets used in this article, including all the LI-6400 data, are available in the Supplementary Materials.

### **References**


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