Most plants live on carbon (C) fixed by their own photosynthesis. But, some forest understory plants including pyroloids have evolved to obtain C through mycorrhizal fungi (i.e. mycoheterotrophy), adapting to dark environments where active photosynthesis is not possible. However, we know little about how trophic strategies and photosynthetic traits change with light conditions. In this study, we investigated natural abundance of carbon isotopes and photosynthetic traits of three Pyroleae species (Pyrola incarnata, P. alpina & Orthilia secunda) in relation to light conditions in subalpine forests on Mt. Fuji. We found that O. secunda was autotrophic even in dark environments. P. alpina and P. incarnata were partially mycoheterotrophic, estimated to acquire 13.7% and 30.2% C from fungi, respectively. Net photosynthetic rate (Pn) and light compensation points (LCP) of P. alpina increased with light availability but leaf ¹³C decreased, suggesting P. alpina rely more on photosynthesis and less fungal C in light conditions. P. incarnata kept relatively constant Pn, LCP and leaf ¹³C, suggesting its heterotrophic level would be less affected by light conditions.