Growth and photosynthesis responses of Phaeodactylum tricornutum todissolved organic matter from salt marsh plant and sediment

The effects of allochthonous dissolved organic matter (DOM) on the growth and photosynthesis of Phaeodactylum tricornutumwere investigated. P. tricornutum incubated in f/2 medium was exposed to DOM additives, which were extracted from the plant andsediment samples of a salt marsh in North Branch of the Yangtze estuary, China. During 12 days incubation, the chlorophyll fluorescenceparameters of P. tricornutum were measured by a Phyto-PAM phytoplankton analyzer. Spectral properties of DOM in algae filtrateswere also observed. The concentrations of chlorophyll a, active chlorophyll a, and the maximum quantum yield of photosystem IIsignificantly decreased after four days of incubation, suggesting that the growth and photosynthetic e ciency of P. tricornutum wereinhibited. After adding sediment-DOM extract, both a250/a365 (the ratio of the absorption coe cients at 250 and 365 nm) and S values(spectral slope coe cients) of algae filtrates declined in the first two days, which demonstrated a loss of low molecular weight DOM.Parallel factor analysis of fluorescence spectra of DOM in algae filtrates revealed that DOM could be classified into two humic-likeand two protein-like components. The fluorescence intensity of tyrosine-like component originating from algae increased significantlyduring incubation. This study supports the hypothesis that allochthonous DOM derived from salt marsh plant and sediment have astrong influence on the adjacent aquatic ecosystems.