| With the rapid development of mariculture, the derect discharge of untreated nutrient-rich effluents containing organic matter, inorganic nitrogen, phosphorus, and other nutrients into the ocean can lead to eutrophication, causing excessive algae growth, disrupting marine ecological balance, and posing serious threats to coastal ecosystems. Therefore, effective treatment and resourcify utilization of aquaculture effluents have become urgent issues. Current methods for treating aquaculture effluents include physical, chemical, and biological approaches. Among them, biological treatment, especially using plants, is popular due to its environmental friendliness. Plants can absorb nutrients such as nitrogen and phosphorus from water, achieving the degradation and treatment of pollutants. Hence, using nutrient-rich aquaculture effluents for plant irrigation not only reduces environment pollution but also cultivates economically viable halophytes, which can maximize resourcify utilization. However, the high salinity of mariculture effluents limits the use of traditional terrestrial plants, it made the selection and cultivation of halophytes that can thrive in high-salinity environments become a hot research topic. While various halophytes have shown certain treatment effects on mariculture effluents, their salinity tolerance range often falls below natural seawater, with some plants posing ecological risks or having poor regional adaptability. Against this background, Salicornia bigelovii, known for its unique salt tolerance, broad ecological adaptability, and economic value, has attracted significant attention. This study aims to explore the adaptability and potential of S. bigelovii in treating aquaculture effluents by analyzing its growth and physiological-biochemical responses under different nutrient concentration and salinity conditions. Through a cross-experiment with four salinity levels (0 mmol/L, 340 mmol/L, 510 mmol/L, and 680 mmol/L) and three eutrophication levels (LNC, MNC, HNC) over 60 days, we monitored the growth indices (aboveground height, number of nodes, number of axillary buds and branches, biomass) and physiological-biochemical indices (chlorophyll content, MDA content) of S. bigelovii to analyze its adaptability to different mariculture effluents. The results showed that, under medium-low nutrient levels, S. bigelovii exhibited strong growth adaptability within the 0-510 mmol/L salinity range. Its aboveground growth height, number of axillary buds and branches, node number, and fresh and dry weight accumulation were significantly higher than those at 680 mmol/L salinity level (P<0.05). Additionally, 340 mmol/L and 510 mmol/L salinity levels were more conducive to its node differentiation, indicating that S. bigelovii can effectively cope with moderate salt stress environments through self-regulation mechanisms and maintain stable growth patterns. When salinity reached 680 mmol/L, its MDA content was significantly higher than those of other salinity levels (P<0.05), indicating it was suffering from significant stress, which also suggested that its salt endurance is limited though it has good salt tolerance,. Moreover, increasing nutrient concentrations effectively reduced the impact of various salinity levels on differential growth of S. bigelovii and mitigated the stress effects at 680 mmol/L salinity, while promoting chlorophyll synthesis. This indicates that S. bigelovii has good adaptability to high-nutrient environments and can effectively absorb and utilize nutrients from aquaculture effluents. Additionally, under combined high-nutrient and high-salinity (680 mmol/L) treatments, S. bigelovii’s growth indices remained relatively stable, and MDA levels did not significantly increase though it was somewhat affected. This further confirmed the important role of increased nutrient concentrations in enhancing plant resistance and survival ability under high-salinity conditions. The reseans maybe that under high-salinity stress, S. bigelovii adopted multiple physiological and biochemical responses: increasing leaf succulence to accumulate salt ions in succulent leaves and green vacuoles, reducing salt ion toxicity; synthesizing osmotic regulatory substances to enhance osmotic regulation capacity, ensuring normal water supply to cells, synthesizing and accumulating osmotic protectants to enhance cell osmotic regulation and maintain water balance; and increasing antioxidant enzyme activity to scavenge reactive oxygen species, reducing cellular damage. The mitigation of stress effects with increased nutrient concentrations may be due to the presence of abundant nitrogen, phosphorus, and trace elements such as iron, copper, zinc, and silicon in the effluents, which are beneficial for plant growth. In summary, S. bigelovii can be used as a phytoremediation plant for treating high-salinity eutrophic mariculture effluents and has the potential for large-scale promotion as a salt-tolerant economic plant. |
