Effect Of Exogenous Salicylic Acid On The Physiological And Biochemical Properties Of Zanthoxylum Armatum Under Waterlogging Stress

Stormy weather caused by global climate change will limit the growing environment for waterlogging sensitive plants.Zanthoxylum armatum DC is a valuable tree in China with significant economic and ecological importance due to its medicinal and food-related properties.However,it is highly vulnerable to water and waterlogging stress,leading to adverse effects such as leaf wilting,fruit and flower drop,and even death.Waterlogging has become a critical limiting factor in the growth of Z.armatum.Therefore,it is essential to take effective measures to enhance plant resistance to waterlogging,which is crucial for ensuring normal growth,maintaining high and stable yields,and preserving good quality.Salicylic acid（SA）is a crucial plant growth regulator that can improve plant resistance to waterlogging by regulating their physiological and biochemical processes under stress.However,the effects of salicylic acid on Z.armatum under waterlogging stress have not yet been studied,and the physiological mechanisms underlying its effects remain unknown.To this end,the present investigation employed Z.armatum seedlings as the experimental material,which were subjected to root irrigation with solutions of salicylic acid（0 m M,1m M and 2 m M）followed by waterlogging treatments of varying durations（0,1,2,3 and 6days）.The physiological response of the seedlings to salicylic acid was assessed by analyzing various morphological,photosynthetic,and physiological and biochemical performance traits under waterlogging stress.The goal was to provide a theoretical framework for enhancing Z.armatum’s resistance to waterlogging and improving its growth adaptability.The primary outcomes of this study are as follows:（1）Waterlogging stress significantly impacted the phenotype of Z.armatum,leading to progressive yellowing,wilting,and leaf abscission,as well as root blackening and rotting.However,exogenous salicylic acid treatment effectively mitigated the damage caused by waterlogging to seedlings,maintaining a healthy phenotype of Z.armatum during the early stages of waterlogging,and delaying the onset of adverse symptoms.（2）Waterlogging stress led to a reduction in leaf photosynthesis in Z.armatum.However,salicylic acid treatment mitigated the loss of photosynthetic pigments due to stress and improved the photosynthetic capacity of seedlings.Salicylic acid-treated plants exhibited higher levels of chlorophyll a（Chl a）,chlorophyll b（Chl b）,total chlorophyll（Total Chl）,and carotenoids（Car）,as well as net photosynthetic rate（P_n）,transpiration rate（T_r）,stomatal conductance（G_s）,water use efficiency（WUE）,and lower intercellular CO₂concentration（C_i）compared to the waterlogged treatment.This suggests that salicylic acid treatment effectively mitigated the damage caused by waterlogging in Z.armatum,highlighting its potential to enhance plant resistance to waterlogging.（3）The chlorophyll fluorescence characteristics of Z.armatum were significantly affected by waterlogging stress,and salicylic acid treatment alleviated the photoinhibition caused by the stress.Salicylic acid treatment effectively improved the maximum photochemical efficiency（F_v/F_m）,actual photochemical efficiency(Φ_PSII),PSII photochemical efficiency（F_v’/F_m’）,and electron transfer efficiency（ETR）of photosystem II（PSII）,while reducing the initial fluorescence（F_o）and non-photochemical quenching（NPQ）.Additionally,salicylic acid treatment enhanced the electron transfer capacity of Z.armatum leaves.（4）Waterlogging stress led to increased oxidative damage in Z.armatum.However,the application of exogenous salicylic acid increased the activities of antioxidant enzymes,such as superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,and ascorbate peroxidase（APX）,which in turn,effectively inhibited the increase in malondialdehyde（MDA）content and relative electrical conductivity（REC）induced by waterlogging stress,and reduced the degree of membrane peroxidation.Furthermore,salicylic acid treatment increased the proline（PRO）content and restored the relative water content（RWC）of leaves,which effectively alleviated osmotic stress.（5）The oxygen-deprived environment during waterlogging stress induced an elevation in the activities of alcohol dehydrogenase（ADH）and pyruvate decarboxylase（PDC）in Z.armatum roots,a shift in root respiratory metabolism to anaerobic respiration.Exogenous treatment with salicylic acid reduced the activities of ADH and PDC,thereby mitigating the toxic effects of the byproducts of incomplete oxidation during anaerobic fermentation and prolonging the survival of the plant under waterlogging stress.（6）Principal component and affiliation function analysis was used to evaluate the alleviating effect of salicylic acid on Z.armatum under waterlogging stress.The results showed that the 1 m M SA treatment had the highest combined value of waterlogging tolerance under 1 d,2 d,3 d and 6 d of waterlogging,followed by the 2 m M SA treatment and the lowest 0 m M SA.Therefore,the application of salicylic acid at a concentration of 1m M to Z.armatum resulted in the best combined waterlogging tolerance.