Photosynthetic performance of temperate seagrasses in Northern Japan

The photosynthetic activity of temperate seagrass species in Akkeshi Bay was assessed using the newly developed submersible, pulse-amplitude modulated (PAM) fluorometer: Diving-PAM. The rapid light curve (RLC) was used to compare the photosynthetic activity of cultured seedlings and mature in situ Zostera marina, Zostera asiatica, Zostera japonica and Phyllospadix iwatensis. Several fluorescence parameters were measured as a function of irradiance generated by the Diving PAM; electron transport rate, quantum yield, photochemical (qP), non-photochemical quenching (NPQ) and recovery period. Seedling and mature species of Z. japonica with less acute alpha had the highest maximum ETR and minimum saturating irradiance. A similar pattern in the photosynthetic activity between cultured seedlings and mature seagrasses was found. A high variation occurred for rapid light curve parameters among species, providing validity to this new PAM fluorometry method in determining species-specific mechanisms and adaptive responses of seagrasses.