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AB prepress abstract   -  DOI: https://doi.org/10.3354/ab00730

Enhanced thermotolerance of photosystem II by elevated pore-water salinity in the coastal marsh graminoid Sporobolus pumilus

Brant W. Touchette*, Sarah R. Schmitt, John W. G. Moody

*Corresponding author:

ABSTRACT: In coastal marsh ecosystems, high salinities, anoxic waterlogged soils, and elevated summer temperatures often promote physiological strain that results in only a few tolerant halophytic species. Although not well understood, plant physiological behavior to multiple stressors can be complex and may involve intensifying or offsetting responses. In this study, physiological responses to combined salinity and high temperature on the coastal marsh graminoid Sporobolus pumilus (syn. Spartina patens) were investigated. Specifically, we considered changes in plant-water relations and photosystem II (PSII) behavior (involving chlorophyll a fluorescence) in heat-shocked plants that were acclimated to different salinities (0, 15, and 30 psu). Higher salinities fostered lower stomatal conductance (g), lower leaf-water potential (Ψleaf) and lower tissue-water content (θ), as well as decreased potential quantum yield (Fv/Fm) and decreased excitation energy capture efficiencies of open reaction centers (Fv´/Fm´). Heat-shocked plants acclimated to freshwater only had decreased Fv/Fm and PSII performance index (PIABS). Interestingly, there were no changes in chlorophyll a fluorescent outputs in heat-shocked plants acclimated to moderate salinities and minimal changes in plants acclimated to high salinities. Approximately 25 percent of the heat-shocked S. pumilus in freshwater revealed a K-step in their polyphasic chlorophyll a fluorescent transients (OJIP procedure); K-steps were not observed in salt-treated plants. This suggests that, for plants residing in freshwater, heat-shock promoted disturbances in the PSII reaction centers and, in some cases, disrupted the oxygen-evolving complex. These PSII disruptions were either absent or less intense in salinity-treated plants, indicating that acclimation to environmental salts may provide PSII thermostability in S. pumilus