A comparative study of maximal quantum yield of photosystem II to determine nitrogen and phosphorus limitation on two marine algae

• We studied Fv/Fm of C. debilis and S. trochoidea in nutrient-depleted cultures.
• For C. debilis, Fv/Fm decreased quickly but it remained unchanged in S. trochoidea.
• For some of the algae, Fv/Fm is not a reliable diagnostic for nutrient limitation.
• S. trochoidea has a higher cellular TN and TP content than that of C. debilis.

We studied the effects of nitrogen and phosphorus supply on Fv/Fm (maximal quantum yield of photosystem II) in the diatom Chaetoceros debilis and dinoflagellate Scrippsiella trochoidea in nitrogen (N) and phosphorus (P) depleted cultures to determine whether this parameter could be used to monitor N or P limitation. In the nutrient depleted experiments, no obvious decrease of cell density and chlorophyll concentration was observed except in N-depleted incubation of S. trochoidea. For C. debilis, Fv/Fm decreased quickly in periods of N- and P-depletion and re-supply of N and P induced a quick recovery of Fv/Fm. However, in S. trochoidea culture, Fv/Fm remained unchanged in N- and P-depleted conditions and addition of sufficient N and P to N- and P-depleted cultures did not affect Fv/Fm. Therefore, Fv/Fm is insensitive to N and/or P limitation in growth of S. trochoidea. The results suggested that Fv/Fm was not a robust diagnostic for nutrient limitation in dinoflagellates. The differences in the sensitivity of Fv/Fm to nutrient limitation may result from different nutrient storage abilities among algal species.