Photoprotection of PSII in Hawaiian lobeliads from diverse light environments

Excess irradiance can reduce the quantum yield of photosynthesis via photoprotective energy dissipation, inactivation or downregulation of PSII. We examined variation in photoprotection as part of a study of adaptive radiation in photosynthetic light responses by Hawaiian lobeliads. We measured the maximum efficiency of PSII (F_v/F_m) and recovery of F_v/F_m after high light stress in field populations of 11 lobeliad species and in four species growing under common-garden greenhouse conditions. Species showed no difference in F_v/F_m (0.82 ± 0.02 (mean ± s.e.)) or in their ability to recover from light stress under field conditions. Average recovery was 74 ± 1.4% within 1 h of removal of the stress suggesting that all species maintain the ability to recover from high light stress, at least in the short-term. In contrast, the results from the common-garden indicate that long-term exposure to high irradiance and associated higher temperatures can cause a sustained reduction in PSII function. Species showed decreased F_v/F_m and percentage recovery as treatment irradiance increased. F_v/F_m and percentage recovery were positively related to native habitat PFD across species, suggesting that there has been a diversification in high light tolerance, with species from sunnier environments better able to avoid sustained declines in PSII function.