Effect of Salinity on Photosynthetic Performance in Cup Plant (Silphium Perfoliatum L.)

Soil salinity is recognized as a critical abiotic stress that limits plant growth on marginal lands. The cup plant (Silphium perfoliatum L.), a perennial bioenergy species with high biomass potential, has been proposed for cultivation on saline-degraded soils; however, its responses to salt stress remain insufficiently characterized. In the present study, the physiological responses of cup plant to neutral (NaCl) and alkaline (NaHCO₃) salt stress at concentrations of 100, 200, and 300 mM were evaluated in a pot experiment conducted under controlled conditions. The assessed indicators included relative chlorophyll content (CCI), chlorophyll a fluorescence parameters (Fv/Fm, Fv/Fo, PI), and gas ex-change characteristics, namely net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E), and intercellular CO₂ concentration (Ci). Dose-dependent de-creases in all measured physiological parameters were induced by salinity. A more pronounced negative effect was observed under alkaline salt stress than under neutral salt stress. For instance, at 300 mM NaHCO₃, chlorophyll content and photosynthetic rate were substantially reduced compared with those recorded under the corresponding NaCl treatment. Even at the moderate salinity level of 100 mM, reductions in photo-synthetic performance were detected relative to the control. Overall, photosynthetic efficiency and gas exchange in cup plant were markedly impaired by salinity, particu-larly under conditions of high bicarbonate concentration. These findings provide new insight into the physiological limitations of S. perfoliatum under acute salt stress and demonstrate that alkaline salinity, associated with elevated pH due to HCO₃⁻, exacer-bates stress effects beyond the osmotic and ionic impacts of neutral salinity.