Physiological Responses of the Submerged Macrophyte Stuckenia pectinata to High Salinity and Irradiance Stress to Assess Eutrophication Management and Climatic Effects: An Integrative Approach

Abstract

Stuckenia pectinata, a submerged macrophyte of eutrophic to hyper-eutrophic fresh to brackish waters, faces management and climatic-forced increment of salinity and irradiance in Vistonis Lake (Greece) that may endanger its existence and the ecosystem functioning. A pre-acclimated clone under low irradiance and salinity conditions was treated to understand the effects of high salinity and irradiance on a suite of subcellular (chlorophyll a fluorescence kinetics and JIP-test, and chlorophyll content) to organismal (relative growth rate—RGR) physiological parameters. The responses to high irradiance indicated the plant’s great photo-acclimation potential to regulate the number and size of the reaction centers and the photosynthetic electron transport chain by dissipation of the excess energy to heat. A statistically significant interaction (p < 0.01) of salinity and irradiance on Chl a, b content indicated acclimation potential through adjusting the Chl a, b contents. However, no significant (p > 0.05) difference was observed on Chl a/b ratio and the RGR, indicating the species’ potential to become acclimatized by reallocating resources to compensate for growth. Thus, the regulation of photosynthetic pigment content and photosystem II performance consisted of the primary growth strategy to present and future high salinity and irradiance stressful conditions due to eutrophication management and the ongoing climatic changes.

Effects of Glyphosate-Based Herbicide on Primary Production and Physiological Fitness of the Macroalgae Ulva lactuca

“…Therefore, the use of non-invasive high-throughput screening tools, such as pulse amplitude modulated (PAM) fluorometry and laser-induced fluorescence (LIF), allows evaluation of the ecotoxicity in photosynthetic organisms [53][54][55][56][57]. While PAM has been widely used as a proxy for the bioenergetics involved in photosynthesis and the physiological effects of different concentrations of contaminants [13,55,[58][59][60] and was previously used to study macroalgae [61], LIF has seen a greater development over the last decade [62,63] and previously used in macroalgae including Ulva [56]. In green leaves, presenting a maximum in the red region (Fr) and at the far-red (Ffr) region of the spectrum, LIF spectra and the Fr/Ffr ratio have a good correlation with the maximum photochemical efficiency of PSII (F v /F m ) and with chlorophyll a concentration, with clear deviations under stress conditions [64].…”