Abstract: Aims Rhizophora stylosa plays a crucial role in coastal plant ecosystems, contributing to environmental pollution remediation, coastline stabilization, and water quality purification and filtration. Cold stress poses a significant challenge to breeding efforts in the modern era, impeding the normal growth of R. stylosa seedlings and consequently impacting the regeneration and distribution patterns of R. stylosa communities. Growth regulators can improve plant stress resistance, and reveal the alleviating effect of growth regulators on photosynthetic characteristics of red sea olive under low temperature stress, could provide a scientific basis and theoretical guidance for the cultivation of R. stylosaseedlings and the prevention and control of low temperature. Methods In this study, the effects of growth regulators on R. stylosa seedlings were investigated by comparing the photosynthetic pigment (chlorophyll a, chlorophyll b, total chlorophyll, carotenoids) content and photosynthesis indexes (net photosynthetic rate, stomatal conductance, intercellular carbon dioxide concentration, transpiration rate) of R. stylosa seedlings under low temperature stress and rewarming. Important findings 1) Low temperature stress inhibited the photosynthetic process of R. stylosa seedlings, significantly reducing the photosynthetic pigment content and photosynthesis indexes of R. stylosa seedlings. 2) Adding appropriate concentrations of growth regulators alleviated the low temperature inhibition, promoted the rewarming effect, and improved the photosynthetic physiological process of R. stylosa. 3) Excessive concentrations of growth regulators (150 mg·L–1 NAA) led to the aggravation of low temperature stress in R. stylosa seedlings, so it was extremely important to screen appropriate species and concentrations. 4) Principal component analysis showed that biennial R. stylosa seedlings had stronger low temperature resistance than annual R. stylosa seedlings. 5) Combined with membership function analysis, 100 and 200 mg·L–1 GA3, 150 mg·L–1 IAA, 400 mg·L–1 6-BA, 200mg·L–1 GA3, and 50 mg·L–1 NAA had better effects under low temperature stress and rewarming.

Key words: plant growth regulator, Rhizophora stylosa, photosynthetic characteristics, low temperature stress, rewarming, mitigation effect