Although intertidal macroalgae are highly tolerant to hyposaline stress, the underlying mechanisms remain poorly characterized. In this study, we investigated the effects of a short-term immersion in hyposaline conditions [5‰ (LSS_5) and 0‰ (LSS_0)] on the physiological characteristics and the transcriptome of Pyropia haitanensis. The hyposaline stress treatment caused more severe damages to the thalli than the hypersaline stress conditions. Decreased growth and energy metabolism may benefit the thalli by redirecting energy to specific stress responses under hyposaline stress. The reactive oxygen species production was lower under LSS_5 compared with LSS_0. Although superoxide dismutase activity and glutathione contents increased under the LSS_0 condition, the freshwater induced more severe oxidative damages. Moreover, P. haitanensis thalli rapidly excreted Na⁺, K⁺, and proline to achieve osmotic balance. However, K⁺ content of cells remained high when thalli were exposed to LSS_5, which is advantageous for the high photosynthesis rate of thalli. The mechanisms behind Na⁺ and K⁺ export and the osmolyte adjustments under hyposaline stress were distinct from hypersaline stress. Additionally, the upregulation of extensins might increase cell wall flexibility to maintain cell turgor pressure and act as a stress signal under LSS_5. The activation of heat shock proteins maintained the protein homeostasis under LSS_0, which may be a signature of the ability of Pyropia spp. to cope with several abiotic stresses in the intertidal zone. The present study paves the way for more detailed investigations of the mechanisms behind the hyposaline stress tolerance of intertidal seaweed.

尽管潮间带大藻类对次盐碱胁迫具有高度的耐受性，但其潜在机制仍知之甚少。在这项研究中，我们调查了短期浸泡在次盐碱条件下[5‰（LSS_5）和0‰（LSS_0）]对海谭拟南芥生理特性和转录组的影响。。与高盐胁迫相比，低盐胁迫治疗对海藻造成的破坏更为严重。生长减慢和能量代谢可能通过在次生理盐水压力下将能量重定向到特定的压力反应而使沙利受益。与LSS_0相比，在LSS_5下的活性氧产生较低。尽管在LSS_0条件下超氧化物歧化酶活性和谷胱甘肽含量增加，但淡水引起了更严重的氧化损伤。此外，海坛假单胞菌迅速排泄Na ⁺，K ⁺和脯氨酸以达到渗透平衡。但是，K ⁺沙利暴露于LSS_5时细胞的含量仍然很高，这有利于沙利的高光合作用率。Na ⁺和K ⁺出口的机制以及次盐胁迫下的渗透压调节不同于高盐胁迫。另外，延伸蛋白的上调可能会增加细胞壁的柔韧性，以维持细胞膨大压力并在LSS_5下充当应激信号。热激蛋白的激活在LSS_0下保持了蛋白质稳态，这可能是远视菌的能力的标志。以应对潮间带的几种非生物胁迫。本研究为潮间带海藻的盐下胁迫耐性机制的更详细研究铺平了道路。