The physiology of photoacclimation and photoprotection in the invasive red alga, Gracilaria salicornia

Abstract

This study compared, in a controlled laboratory setting, pulse amplitude modulation fluorometer (PAM) and dissolved oxygen (DO) parameters in high (HI) and low (LI) irradiance acclimated Gracilaria salicornia, an invasive red alga. We determined that both PAM and DO techniques similarly discriminate between HI and LI and are significantly correlated in most parameters. HI results diverge, but results from LI samples do not. The hypothesis is presented that the divergence between PAM and DO at super-saturating irradiance may be an artifact arising from PAM's concurrent measurement of non-photochemical quenching (NPQ). The results are shown to be reconciled if the energy diverted to NPQ is added to the PAM rates of electron transport. In addition, it appears that PAM ETRmax predicts net DO and may have the potential to predict macroalgal growth. Thus, Diving PAM appears to be a useful in situ method of assessing the photosynthetic poise of macroalgae.