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 responses to multiple stressors can be complex and may involve intensifying or offsetting reactions. In this study, we investigated physiological responses to combined salinity and high temperature in the coastal marsh graminoid Sporobolus pumilus (syn. Spartina patens). Specifically, we considered changes in plant-water relations and Photosystem II (PSII) behavior (involving chlorophyll [chl] 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 (Ψ_leaf) and lower tissue-water content (θ), as well as decreased potential quantum yield (F_v/F_m) and decreased excitation energy capture efficiencies of open reaction centers (F_v’/F_m’). Heat-shocked plants acclimated to freshwater only had decreased F_v/F_m and PSII performance index (PI_ABS). Interestingly, there were no changes in chl a fluorescent outputs in heat-shocked plants acclimated to moderate salinities, and minimal changes in plants acclimated to high salinities. Approximately 25% of the heat-shocked S. pumilus in freshwater revealed a K-step in their polyphasic chl 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.

中文翻译：

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沿海沼泽粒状短小孢子虫（Sporobolus pumilus）的孔隙水盐度提高，增强了光系统II的耐热性

摘要：在沿海沼泽生态系统中，高盐度，缺氧的涝渍土壤和夏季升高的温度通常会促进生理应变，导致只产生少数可耐受的盐生植物。尽管尚未充分了解，但植物对多种胁迫的生理反应可能很复杂，可能涉及强化或抵消反应。在这项研究中，我们调查了沿海沼泽粒状短小孢子虫（Spartina patens）对盐度和高温的生理响应。具体来说，我们考虑了植物与水的关系和光系统II（PSII）行为的变化（涉及叶绿素[chl] a适应不同盐度（0、15和30 psu）的热激植物中。更高盐度促进低气孔导度（克），低级叶水势（Ψ_叶）和较低的组织水含量（θ），以及电位降低量子产率（˚F _v / ˚F_米）和降低的激发能量俘获效率打开反应中心（F _v '/ F _m '）。适应淡水的热激植物仅具有降低的F _v / F _m和PSII性能指数（PI _ABS）。有趣的是，在适应中度盐度的热激植物中chl a荧光输出没有变化，而适应高盐度的植物中chl a荧光输出也没有变化。淡水中约有25％的热休克短链霉菌在其多相细胞中呈现出一个K阶跃，即荧光瞬变（OJIP程序）。在盐处理过的植物中未观察到K步。这表明，对于居住在淡水中的植物，热激促进了PSII反应中心的紊乱，并在某些情况下破坏了放氧复合物。在经过盐度处理的植物中，这些PSII破坏不存在或强度较小，这表明适应环境盐可以在短链霉菌中提供PSII热稳定性。。