Tolerance of Phyllospadix scouleri seedlings to hydrogen sulfide

• Phyllospadix scouleri seedling health is reduced when exposed to H2S.
• LD50 for P. scouleri seedlings is 430 μM at 48 h and 86 μM after 7 days.
• Photosynthetic rates (Qmax) decrease with high levels of H2S.
• PSII became inactive whereas PSI remained active at high levels of H2S.
• Levels of H2S found in the field suggest H2S may be limiting seedling recruitment.

Phyllospadix scouleri is a common seagrass along the rocky intertidal coast of the Pacific Northwest. Previously we established a correlation between increased sulfide and hydrogen sulfide (H2S) and Zostera marina seedling senescence. While Z. marina grows in soft sediment environments, here we evaluate the possibility that P. scouleri may experience similar decreases in health when exposed to increasing H2S loading. To do this, seedlings were immersed in various concentrations of H2S, in axenic media, and photosynthetic and respiratory output was measured. We found that at high doses (mM) of H2S Photosystem II was inhibited whereas Photosystem I remained active. At lower levels, total photosynthetic output decreased with increasing H2S concentrations. Using these data we produced an LD50 of 430 μM at 48 h and 86 μM at 7 days. Our study confirms that Phyllospadix seedlings are also vulnerable to increasing sulfide loads.