To investigate the effects of water stress and subsequent recovery on the water potential, photosynthetic and chlorophyll fluorescence characteristics of Michelia × alba sapling, a widely utilized greening tree species in the south subtropical region.

Twelve open-topped chambers (OTCs) with isolated groundwater were utilized, each containing one Michelia × alba sapling. A randomized block design was employed to set up four water gradient treatments, incorporating both rainfall interception in the undercanopy and artificial irrigation: Over-irrigation (OW), control (CK), moderate drought (MD), and high drought (HD). The dynamic changes in instantaneous water potential, photosynthesis and chlorophyll fluorescence parameters of the Michelia × alba leaves were measured under different water stress treatments (3 consecutive months) and subsequent water recovery (2 consecutive months), and the differences between treatments were analyzed.

Compared with CK, drought stress (MD and HD) significantly reduced the leaf water potential index (midday water potential), photosynthetic indices (net photosynthetic rate, stomatal conductance, etc.), and chlorophyll fluorescence indices (maximum photochemical efficiency, electron transport rate, etc.) of Michelia × alba saplings. In contrast, excessive water irrigation had no significant effect on the leaf water potential, photosynthesis, and fluorescence indices of Michelia × alba saplings. After continuous natural atmospheric precipitation, the leaf water potential, photosynthesis, and chlorophyll fluorescence indices of Michelia × alba saplings under drought stress (MD and HD) recovered and showed no significant differences compared with those of the CK. After the soil moisture was restored, there were no significant differences in the water potential, photosynthesis, and fluorescence indices among different treatment groups.

Drought stress limits the leaf water potential, photosynthesis, and fluorescence of Michelia × alba sapling leaves, causing wilting and negatively affecting growth. Timely watering can restore the plants to normal conditions. Specifically, before the soil moisture falls below 25% of the field capacity, timely artificial watering should be applied to replenish the soil moisture. Atmospheric precipitation effectively mitigates the suppression of Michelia × alba sapling's water potential, photosynthetic fluorescence due to soil drought, promoting recovery and growth. In the maintenance and management process of urban landscaping plants like Michelia × alba, when continuous drought occurs, attention should be paid to the soil moisture index. Timely watering can help Michelia × alba recover from water stress and avoid death.