Effects of exogenous H2S treatment on physiological characteristics of salt-alkali stressed seedling of Malus halliana

Abstract:【Objective】The loess plateau production area in northwest China is the dominant production area of apple in China. Due to the abundant sunshine and large temperature difference between day and night, the area of apple cultivation has been expanding continuously. According to statistics, the saline- alkali land area accounts for 1/5 of the total arable land in China, while the saline-alkali area in the in- land northwest is larger, accounting for more than 13% of the total saline-alkali area. Therefore, in order to improve fruit quality, plant stress resistance and physiological metabolism, it is particularly important to choose appropriate exogenous substances to alleviate salt stress. In this study, the effects of exogenous hydrogen sulfide (H2S) on photosynthesis and physiological characteristics of Malus halliana seed- lings with 8 mature leaves grown under saline-alkali stress were studied by spraying different concentra- tions of H2S.【Methods】The experiment adopted potted seedlings of M. halliana at 8-leaf age and irri- gated with water or saline water (100 mmol · L- 1 NaCl + NaHCO3 solution, saline- alkali stress). A total of 6 treatments were applied, namely, water irrigation (CK1), saline-alkali stress (CK2), saline-alkali stress+0.1mmol·L-1 NaHSspraying(T1),saline-alkalistress+0.2mmol·L-1 NaHSspraying(T2),sa- line-alkali stress +0.3mmol·L-1 NaHS spraying (T3), and saline-alkali stress + 0.4mmol·L-1 NaHS spray- ing (T4). The saline water was sprayed onto the seedlings at 500 mL per pot, and NaHS solution was sprayed to the leaves at 18:00 every day. During the stress treatment, 500 mL of clean water was irrigat- ed regularly from 17:00 to 18:00 every 5 days, and various indicators were measured and analyzed at 0 d, 10 d, 20 d and 30 d after stress treatment. Chlorophyll content, photosynthetic characteristics, fluores- cence parameters, antioxidant enzymes, membrane leakage and osmotic regulating substances were de- termined and their correlations were analyzed【. Results】The results showed that with the extension of salt stress time, chlorophyll a, chlorophyll b, chlorophyll a + b, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), the initial fluorescence (F0), and the coefficient of photochemi- cal quenching (qP) decreased. Intercellular CO2 concentration (Ci), regulatory energy dissipation (Y (NPQ)), non-regulatory energy dissipation (Y(NO)), and relative conductivity (REC) increased. Proline (Pro), superoxide dismutase (SOD) and peroxidase (POD) increased initially but declined later. Com- pared with CK2, the increase or decline in each parameter was smaller under exogenous H2S treatments. At 30 days under stress, the REC in treatment groups decreased by 13.54% to 37.92% and Pro de- creased by 8.39% to 24.48%. H2S treatment had a concentration effect. Under T2 treatment, Chl a, Chl b, Chl a+b, Pn, Gs, Tr, F0, and qP had the lowest decrease, and were significantly higher than CK2 but lower than CK1. Y(NPQ), Y(NO) and REC increased the most. The changes in Pro, SOD and POD were the most obvious. Correlation analysis showed that Pn was positively correlated with Gs, Tr, F0, and qP, while negatively correlated with REC, Ci, Y(NO) and Y(NPQ). The above parameters were standard- ized, and principal component analysis was conducted to extract two principal components with a char- acteristic value of 14.783 and 2.781, respectively. The variance contribution rate was 82.128% and 15.452%, respectively. According to the ranking of principal component scores, the ability of exoge- nous H2S to alleviate salt-alkali stress in M. halliana from high to low was CK1 > T2 > T1 > T3 > T4 > CK2.【Conclusion】Exogenous H2S reduced the decrease of photosynthesis and the degradation of chlo- rophylls caused by saline-alkali stress in the seedlings of M. halliana. It effectively alleviates the oxida- tive damage caused by saline-alkali stress, and reduces membrane damage under stress. Exogenous H2S at 0.2 mmol·L-1 was found to be most effective to improve the photosynthetic capacity, increase antioxi- dant enzyme activity and promote stability of membrane of M. sinensis under saline-alkali stress.