Flexible and reversible responses to different irradiance levels during photosynthetic acclimation of Cypripedium guttatum

Cypripedium guttatum can be found both in open and shady habitats. Photosynthetic acclimation of C. guttatum to different light availabilities was detected using measurements of chlorophyll fluorescence, photosynthesis and leaf traits. When growing under low light conditions, C. guttatum exhibited a greater efficiency in photochemical utilization of absorbed light energy, and a lower ability for non-photochemical dissipation of excess light energy, as compared to the plants growing under high light conditions. Under intermediate light conditions, C. guttatum exhibited higher photosynthetic capacity (Amax) than those under both low light or high light conditions. The differences in Amax among three light environments was linked to the differences in biochemical efficiency, leaf N content (LNC) and leaf dry mass per unit area (LMA), but not to the differences of chlorophyll content. However, there were no significant differences in the light compensation points (LCP) and light saturation points (LSP) for photosynthesis for the plants growing under the three light conditions. These results indicate that the photosynthetic capacity of C. guttatum leaves allows for flexible and reversible responses to different irradiance levels. Photosynthetic acclimation in C. guttatum was affected by biochemical changes, the changes in LMA and ratio of Chl a/b. Successful acclimation of C. guttatum to a broad range of light levels likely allows for its wide geographical distribution. A level of about 45% sunlight appears to be optimal for photosynthesis.