Comprehensive Evaluation and Identification Index Screening of Soybean Salt Tolerance Based on Chlorophyll Fluorescence Kinetic Parameters

Objective This study aimed to investigate the responses of different soybean varieties to NaCl stress and to identify effective indicators for evaluating soybean salt tolerance.

Methods Nine soybean varieties were used as experimental materials. At the second-trifoliate leaf stage, the plants were subjected to salt stress by applying a nutrient solution containing 250 mmol·L⁻¹ NaCl, while a nutrient solution without NaCl was used as the control. After the salt concentration reached 0.6%, the chlorophyll fluorescence kinetic parameters of the third true leaves were measured using a plant efficiency analyzer. Multivariate statistical analysis was then employed to comprehensively evaluate the salt tolerance of the soybean varieties.

Results The responses of different soybean varieties to salt stress varied. Dongnongdou 253 exhibited higher salt tolerance than the other eight varieties, while Suinong 53 was more sensitive. Through principal component analysis, the salt tolerance coefficients of 18 individual indicators were transformed into three independent comprehensive indicators, with a cumulative contribution rate of 91.215%. The comprehensive evaluation value (D value) was calculated using the membership function method, and the nine soybean varieties were classified into three groups by cluster analysis. A mathematical evaluation model for soybean salt tolerance was established using stepwise regression analysis: D=1.388Area+0.385φEo−0.585, R²=0.991, in which Area and φEo could serve as rapid identification indicators for evaluating soybean salt tolerance.

Conclusion Compared with salt-sensitive soybean varieties, the strongly salt-tolerant varieties exhibited weaker inhibition of PSⅡ reaction center activity under salt stress and maintained a relatively higher capacity for photosynthetic electron transport.