Objective To analyze the effects of different water treatments on the growth of resistant tree species Lagerstroemia speciosa, explore the response mechanism of morphological traits of L. speciosa, and provide a theoretical basis for the selection and water management of resistant landscape tree species.

Method Using the one-year-old seedlings of L. speciosa as materials, a 30-day water stress experiment was conducted by setting up four types of water treatments, drought (DR), waterlogging (WL), waterlogging-drought alternating (WD), and control (normal water supply, CK). Subsequently, the water stress was relieved and the soil moisture in the DR, WL and WD treatments was maintained at the CK level for a 30-day recovery period of growth. The leaf traits, root traits and biomass indicators of plants after water stress and relief were measured.

Result Total leaf areas of L. speciosa significantly decreased at the end of DR, WD stress and at the end of recovery after WL stress compared with CK. Leaf tissue densities of the three water stress treatments were significantly higher at the end of stress compared to CK, and specific leaf areas were significantly lower at the end of recovery. Compared with CK, the WL and WD treatments increased the rates of fine root length and the rates of fine root surface area at the end of stress. At the end of recovery, the rates of fine root surface area were higher in the DR, WL and WD treatments by 9.59%, 12.42%, and 13.57%, respectively, compared to CK. At the end of stress and recovery, the specific root length and specific root surface area in WL treatment was significantly higher compared to CK. At the end of stress, plants under the three water stress treatments increased biomass allocations to stems, and WL treatment plants grew adventitious roots that accounted for 26.95% of total root biomass. Under DR treatment, the root biomass allocation at the end of stress and recovery significantly increased, and the root-shoot ratio increased by 40.93% and 70.06% respectively, compared to their own CK. Correlation analysis showed that there was a trade-off relationship among leaf traits and root traits respectively. Root length, root surface area, and leaf tissue density were significantly positively correlated, and root growth had a positive effect on the leaf tissue density.

Conclusion There is a certain correlation between leaf and root traits. Short term water stress can promote the root growth of L. speciosa seedlings, making them better adapt to the complex and varied water environment of urban landscaping and green spaces.