Alleviation Effects and Mechanisms of Alginate Oligosaccharides and Astaxanthin on Lettuce Growth under Salt Stress

LI Xifeng; XU Zihang; WU Xinyu; YUAN Zhengzheng; CHEN Yufeng; GUO Jingli

doi:10.15933/j.cnki.1004-3268.2026.01.011

Abstract：This study investigated the effects of different addition levels of alginate oligosaccharides and astaxanthin separately on the growth,root morphology,nutrient uptake,and stress resistance of lettuce under salt stress to provide scientific basis and practical experience for lettuce cultivation under adverse conditions.A hydroponic experiment was conducted using Dasu lettuce.We adjusted the nutrient solution to a salt concentration of 120 mmol/L using NaCl solid to simulate the salt stress environment(S).Two types of treatments were set up:alginate oligosaccharides were added at concentrations of 0,0.005%,0.010%,0.015%,0.020%and 0.025%,corresponding to S-B0,S-B1,S-B2,S-B3,S-B4 and S-B5,respectively;astaxanthin was added at concentrations of 0,0.05%,0.10%,0.15%,0.20%and 0.25%,corresponding to S-A0,S-A1,S-A2,S-A3,S-A4 and S-A5,respectively.Meanwhile,the nutrient solution without NaCl added was used as the control treatment(CK),with three replicates per treatment.We analyzed various indicators of lettuce plants,including biomass,growth status,nutrient uptake,root morphology,leaf osmotic regulators and the activity of key antioxidant enzymes.Our experimental results indicated that alginate oligosaccharides promoted the accumulation of root biomass,and the increase of leaf SPAD value and the number of leaves compared to S-B0 treatment.The nitrogen,phosphorus and potassium uptake in S-B1 to S-B5 treatments increased by 47.32%to 89.09%(p<0.05),4.32%to 20.38%and 2.29%to 24.79%,respectively.The total root length,root surface area and root volume increased by 58.83%to 139.04%,53.57%to 92.33%and 36.07%to 72.50%(p<0.05),respectively.Root classification evaluation showed that the addition of alginate oligosaccharides primarily promoted the growth of roots at levelsⅠtoⅢ.At the same time,the average root diameter and root-to-shoot ratio increased by 11.54%to 34.62%and 18.60%to 32.56%,respectively.Compared to S-A0 treatment,the astaxanthin promoted the accumulation of root biomass,leaf SPAD values and the number of leaves.The nitrogen,phosphorus,and potassium uptake in S-A1 to S-A5 treatments increased by 32.11%to 145.95%,10.07%to 66.91%and 25.42%to 64.51%,respectively.The total root length,root surface area and root volume increased by 26.57%to 128.97%,26.59%to 129.01%and 26.67%to 193.33%,respectively.Root classification evaluation showed that the addition of astaxanthin primarily promoted the growth of roots at levels Ⅰ to Ⅱ.At the same time,the average root diameter increased by 10.00%to 33.33%,and there were no significant differences in the root-to-shoot ratio among the treatments.Under salt stress,the addition of alginate oligosaccharides and astaxanthin significantly increased the proline(Pro)content in the leaves,helping to regulate osmotic balance.At the same time,both treatments enhanced the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)as well as reduced the accumulation of malondialdehyde(MDA),thereby decreasing cellular oxidative damage.Redundancy analysis indicated that the addition of alginate oligosaccharides mainly enhanced the activity of SOD,which helped alleviate the damage caused by salt stress to lettuce growth.On the other hand,astaxanthin promoted lettuce's stress tolerance primarily through the combined effects of SOD and Pro,driving its adaptive growth under stress conditions.According to the membership function method,which was used to evaluate various indicators of lettuce,the highest score in alginate oligosaccharide treatments was observed in S-B3 treatment,while in the astaxanthin treatments,the highest score was found in S-A2 treatment.The application of alginate oligosaccharides or astaxanthin in hydroponic vegetable production can both promote the growth of lettuce roots and enhance nutrient absorption.These treatments effectively improve the osmotic balance of leaf cells,while also increase the activity of antioxidant protective enzymes to mitigate the negative effects of salt stress on leafy vegetables.The optimal addition rates for improving the salt tolerance of lettuce are 0.015%for alginate oligosaccharides and 0.10%for astaxanthin.