Photosynthetic Performance of Tidally Flooded Spartina Alterniflora Salt Marshes

Spartina alterniflora has a distinct flood-adapted morphology, and its physiological responses are likely to vary with differences in tidal submergence. To understand these responses, we examined the impacts of tidal inundation on the efficiency of Photosystem II (phi PSII) photochemistry and leaf-level photosynthesis at different canopy heights through a combination of in situ chlorophyll fluorescence (ChlF), incident photosynthetically active radiation, and tide levels. Our result showed small declines (7%-8.3%) in phi PSII for air-exposed leaves when the bottom canopies were tidally submerged. Submerged leaves produced large reductions (30.3%-41%) in phi PSII. Our results suggest that when submerged, PSII reaction centers in S. alterniflora leaves are still active and able to transfer electrons, but only at similar to 20% of the typical daily rate. We attribute this reduction in phi PSII to the decrease in the fraction of open PSII reaction centers (10% of the total) and the stomatal conductance rate caused by the tidal submergence. To our knowledge, this flooding induced leaf-level reduction of phi PSII for S. alterniflora in field settings has not been reported before. Our findings suggest that canopy-level phi PSII is dependent on the proportion of submerged versus emerged leaves and highlight the complexities involved in estimating the photosynthetic efficiency of tidal marshes.

Automated summary

The efficiency of photosynthesis in Spartina alterniflora is affected by tidal inundation, especially in the lower canopy. Our study found that submerged leaves experience a significant decrease in photosynthetic efficiency, mainly due to a reduction in the number of open photosystem II reaction centers and a decrease in stomatal conductance. This highlights the impact of wet environments on the photosynthetic efficiency of Spartina alterniflora.