Abstract:

【Objective】This study investigated the alleviation mechanism of exogenous salicylic acid (SA) on Ginkgo biloba under NaCl stress, with the aim of providing a theoretical basis for addressing the salt damage of G. biloba in saline environments. This could support the expansion of G. biloba cultivation and enhance the plant landscape in these areas.【Method】Thirteen treatment groups were established with NaCl concentrations of 50 (N1), 100 (N2), and 200 (N3) mmol/L, and SA concentrations of 0.02 (S1), 0.10 (S2), and 0.50 (S3) mmol/L, using four-year-old G. biloba as the test material. The groups included CK, N1, N1S1, N1S2, N1S3, N2, N2S1, N2S2, N2S3, N3, N3S1, N3S2, and N3S3, with five replicates per group. The experiments were conducted in the greenhouse of Beijing Forestry University (116° 35'E, 40° 01'N) over a period of 28 days. The average temperature in the greenhouse was approximately 27.5 °C, and the average humidity is about 65.9%. This study observed the phenological characteristics of G. biloba growth and measured various indicators, including leaf fresh weight, chlorophyll a (Chla) content, chlorophyll b (Chlb) content, total chlorophyll (total Chl) content, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), transpiration rate (Tr), maximal photochemical efficiency (F_v/F_m), photochemical quenching coefficient (qP), actual photochemical efficiency (Y(Ⅱ)), and electron transport rate (ETR). The optimal SA concentration for mitigating salt stress in G. biloba was determined through principal component analysis and affiliation function method analysis.【Result】(1) As the NaCl concentration increased and the stress duration extended, the branch tops and leaves of G. biloba exhibited varying degrees of yellowing, scorching, and abscission, with a significant reduction in leaf fresh weight compared to the control group. (2) Increasing NaCl concentration and prolonging stress durations decreased leaf fresh weight, Chla content, Chlb content, total Chl content, Pn, Gs, Ci, Tr, F_v/F_m, qP, Y(Ⅱ), and ETR in G. biloba. (3) The application of exogenous SA at appropriate concentrations alleviates the inhibitory effected of NaCl stress on the growth and photosynthetic characteristics of G. biloba. The N1S2, N2S2, and N3S2 treatment groups were the most effective in mitigating salt damage. (4) Principal component analysis indicated that the exogenous application of SA primarily enhanced salt tolerance by influencing eight indicators: leaf fresh weight, Chla content, Chlb content, total Chl content, Pn, Gs, Tr, and F_v/F_m. (5) Based on the principal component analysis and affiliation function method analysis, the mitigating effect of SA was ranked as follows: 0.10 mmol/L > 0.02 mmol/L > 0.50 mmol/L.【Conclusion】The SA at 0.02 and 0.10 mmol/L under NaCl stress is more effective in mitigating growth and photosynthesis in G. biloba, with 0.10 mmol/L SA showing the best mitigation effect and 0.50 mmol/L SA having a more limited effect. Growth indicators and photosynthetic properties are important reference indicators for assessing salt tolerance in plants. However, the plant responses to salt stress are complex, so this experiment can serve as one references, and further research at physiological, biochemical, and molecular levels is needed.

Key words: Ginkgo biloba, NaCl stress, exogenous SA, phenological characteristics, leaf fresh quality, photosynthesis