Effects of humidity-cold combined stress at the seedling stage in direct-seeded indica rice

•Humidity-cold combined stress affected seedling growth via hampering photosynthesis and tricarboxylic acid cycle.•High humidity not low humidity destroyed photosynthetic and respiratory system of direct-seeded rice under cold stress.•Whether High or low humidity differed physiological traits induced by cold condition of cold-sensitive rice cultivar.•High humidity-cold combined stress increased antioxidant protective enzymes activity and osmotic substances.•Low humidity tended to decrease the physiological damage caused by low temperature after recovery treatment.