Blue honeysuckle (Lonicera caerulea L.) is a deciduous shrub with perennial rootstock found in China. The objectives of this study were to explore the drought tolerance of blue honeysuckle, determine the effect of drought stress on two photosystems, and examine the mechanism of acquired drought tolerance. In this study, blue honeysuckle under four levels of simulated field capacity (100%, 85%, 75%, and 65% RH) was grown in split-root pots for drought stress treatment, for measuring the changes in chlorophyll content, photosynthetic characteristics, and leaf chlorophyll fluorescence parameters. The chlorophyll content of each increased under mild stress and decreased under moderate and severe stress. The net photosynthetic rate, transpiration rate, intercellular carbon dioxide concentration, and stomatal conductance of blue honeysuckle decreased with the increase in water stress. However, the water utilization rate and stomatal limit system increased under mild and moderate stress and decreased under severe stress. The maximum fluorescence (Fm), maximum photochemical efficiency, and quantum efficiency of photosystem II decreased with the decrease in soil water content, and the initial fluorescence increased significantly (p < 0.01). With the decrease in soil water content, the energy allocation ratio parameters decreased under severe drought stress. The main activity of the unit reaction center parameters first increased and then decreased. ABS/CSm, TRo/CSm, ETo/CSm, and REo/CSm gradually declined. After a comprehensive analysis, the highest scores were obtained under adequate irrigation (CK). Overall, we concluded that the water irrigation system of blue honeysuckle should be considered adequate.

The objectives of this research were to analyze anthocyanins in blue honeysuckle (Lonicera caerulea L.), bilberry (Vaccinium vitis-idaea L), and cranberry (Vaccinium macrocarpon Ait.), using HPLC-ESI-QTOF-MS², Fourteen, fifteen, and eight anthocyanins were identified in blue honeysuckle, bilberry, and cranberry, respectively. Cyanidin-3-glucoside (C3G) and peonidin-3-glucoside were detected in all three types of berries, with blue honeysuckle showing the highest C3G content at 5686.28 mg/100 g DW. Total phenolic content (TPC) and total flavonoid content (TFC), along with ABTS, DPPH, and FRAP assays, were measured. Blue honeysuckle exhibited the highest levels of TPC and TFC. The SOD, POD, and CAT activities in blue honeysuckle were 1761.17 U/g, 45,525.65 U/g, and 1043.24 U/g, respectively, which were significantly superior to those in bilberry and cranberry. The antioxidant mechanisms of these enzymes were investigated by molecular docking, C3G showed a higher affinity for POD, confirming the effectiveness of C3G as an antioxidant.