Photosynthesis is one of the parameters first affected by freezing stress. So studying the efficiency of photosynthetic parameters could be an effective strategy in screening freezing-tolerant genotypes. An experiment was conducted to assess freezing temperature effects (0oC, −4oC, −8oC, −12oC, −16oC, −20oC, and −24oC) on two faba bean landraces (Borujerd and Neyshabur). Leaf chlorophyll and carotenoid content were decreased as the temperature declined below 0C. Net photosynthetic and transpiration rate declined earlier in Neyshabur, whereas a relatively constant trend was observed in Borujerd at temperatures between 0oC and −12oC. A 43% greater Np was recorded in Borujerd than Neyshabur at −12oC. Np recovered by 30% and 36% in Borujerd and Neyshabur, respectively, on Day 14 compared with the second day of the recovery period. Except for Ci, which showed a relatively constant trend, the other parameters showed a decreasing trend till 7 days after freezing stress (DAF). WUEi increased more significantly in Neyshabur than in Borujerd after the seventh day of the recovery period. With a subtle evaluation of the landraces\\\' freezing tolerance, both landraces LT50su and RDMT50 remained up to −10oC and −12.5oC, respectively, indicating faba bean plants (the landraces here) can tolerate freezing stress up to −10oC (by enduring minor damages). The positive relationship between the survival percentage and Np indicated that Np could be a reliable criterion to screen freezing-tolerant faba beans at early growth stages.

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