Physiological Responses and Salt Tolerance Evaluation of Different Varieties of <i>Bougainvillea</i> under Salt Stress

Soil salinization significantly impacts the ecological environment and agricultural production, posing a threat to plant growth. Currently, there are over 400 varieties of <i>Bougainvillea</i> with horticultural value internationally. However, research on the differences in salt tolerance among <i>Bougainvillea</i> varieties is still insufficient. Therefore, this study aims to investigate the physiological responses and tolerance differences of various <i>Bougainvillea</i> varieties under different concentrations of salt stress, reveal the effects of salt stress on their growth and physiology, and study the adaptation mechanisms of these varieties related to salt stress. The experimental materials consisted of five varieties of <i>Bougainvillea</i>. Based on the actual salinity concentrations in natural saline-alkali soils, we used a pot-controlled salt method for the experiment, with four treatment concentrations set: 0.0% (<i>w</i>/<i>v</i>) (CK), 0.2% (<i>w</i>/<i>v</i>), 0.4% (<i>w</i>/<i>v</i>), and 0.6% (<i>w</i>/<i>v</i>). After the <i>Bougainvillea</i> plants grew stably, salt stress was applied and the growth, physiology, and salt tolerance of the one-year-old plants were systematically measured and assessed. The key findings were as follows: Salt stress inhibited the growth and biomass of the five varieties of <i>Bougainvillea</i>; the ‘Dayezi’ variety showed severe salt damage, while the ‘Shuihong’ variety exhibited minimal response. As the salt concentration and duration of salt stress increase, the trends of the changes in antioxidant enzyme activity and osmotic regulation systems in the leaves of the five Bougainvillea species differ. Membrane permeability and the production of membrane oxidative products showed an upward trend with stress severity. The salt tolerance of the five varieties of <i>Bougainvillea</i> was comprehensively evaluated through principal component analysis. It was found that the ‘Shuihong’ variety exhibited the highest salt tolerance, followed by the ‘Lvyehuanghua’, ‘Xiaoyezi’, ‘Tazi’, and ‘Dayezi’ varieties. Therefore, <i>Bougainvillea</i> ‘Shuihong’, ‘Lvyehuanghua’, and ‘Xiaoyezi’ are recommended for extensive cultivation in saline-alkali areas. The investigation focuses primarily on how <i>Bougainvillea</i> varieties respond to salt stress from the perspectives of growth and physiological levels. Future research could explore the molecular mechanisms behind the responses to and tolerance of different <i>Bougainvillea</i> varieties as to salt stress, providing a more comprehensive understanding and basis for practical applications.