Drought resistance mechanisms mediated by brassinosteroids in ecological slope protection plants growing in vegetation concrete

To reveal the regulatory effects and mechanisms of action of brassinosteroids on Cassia glauca growth in vegetation concrete under drought stress. Drought conditions were simulated via the pot water control method. Three treatments were established: well-watered, light drought, and severe drought. Additionally, brassinosteroids were sprayed at concentrations of 0 (CK), 0.05 (T1), 0.2 (T2), and 0.5 (T3) mg·L-1 to investigate the effects of brassinosteroids on growth, photosynthesis, and stress resistance indicators of C. glauca under varying drought levels in vegetation concrete. At 90 days of mild drought, compared with the control group, the net photosynthetic rate, stomatal conductance and transpiration rate of C. glauca under the T2 treatment increased by up to 6.29%, 11.93% and 4.79% respectively. At 90 days of severe drought, the underground biomass increased by 20.18% under the T2 treatment, while the intercellular CO2 concentration and malondialdehyde content decreased by 8.29% and 24.1%, respectively. Under the T3 treatment, the plant height, aboveground biomass and proline content increased by up to 28.17%, 17.24% and 12.53%, respectively. It was concluded from principal component analysis that at 90 days of drought, the treatment effect of spraying 0.2 mg·L-1 (T2) brassinosteroids was the best under normal water supply and mild drought conditions, while the treatment effect of spraying 0.5 mg·L-1 (T3) brassinosteroids was the best under severe drought conditions. This indicates that brassinolide can promote the growth and development of C. glauca in vegetation concrete under drought stress, enhance photosynthetic capacity, and regulate the content of osmotic substances to reduce the negative effects of drought stress.