Abstract: To clarify the effects of low-temperature stress on photosynthetic characteristics and yield of rapeseed(Brassica napus L.), a temperature-controlled freezing experiment was carried out using Qingza 15 at Guide Agrometeorological Experimental Station of Hainan Tibetan Autonomous Prefecture, Qinghai Province from April to September 2025. Six temperature gradients of -4 ℃, -5 ℃, -6 ℃, -7 ℃, -8 ℃ and -10 ℃ were set, with two duration treatments of 1 h and 2 h. Potted rapeseed grown under natural field conditions was taken as the control (CK). Chlorophyll content, photosynthetic parameters and yield indices were determined. The results showed that freezing injury inhibited chlorophyll accumulation in rapeseed, and the stress intensified with decreasing temperature and prolonged duration. Freezing treatments reduced net photosynthetic rate, stomatal conductance and transpiration rate of leaves to varying degrees, and the stress aggravated as temperature declined and treatment time extended. Net photosynthetic rate was relatively sensitive, which decreased significantly under the treatment of -4 ℃ for 2 h compared with CK. Transpiration rate and stomatal conductance declined significantly relative to CK when temperature was lower than or equal to -5 ℃, while intercellular CO₂ concentration decreased firstly and then increased. Freezing injury significantly reduced rapeseed grain yield by 23.38%-86.67% (P<0.01). Yield was reduced by more than 50% compared with CK under treatments of temperatures ≤-6 ℃ for 1 h and temperatures ≤-5 ℃ for 2 h, representing severe yield losses.

Key words: rapeseed (Brassica napus L.), low-temperature freezing injury, physiological indices, photosynthetic characteristics, yield