Cunninghamia lanceolata cannot Depend solely on xylem embolism resistance to Withstand prolonged seasonal drought

As global climate change leads to increased spatial and temporal heterogeneity in precipitation patterns, seasonal droughts are becoming more frequent in subtropical monsoon regions. Some conifer species despite having high embolism resistance, still succumb to the effects of climatic drought. Therefore, assessing a plant’s drought resistance based solely on hydraulic traits does not provide a comprehensive picture. Cunninghamia lanceolata (C. lanceolata), a species extensively cultivated in the subtropical monsoon regions due to its rapid growth, drought resistance, and high economic value, plays a dominant role in fast-growing and high-yielding forestry. Investigating the drought response of C. lanceolata is crucial for ensuring sustainable timber production, maintaining ecosystem balance, and enhancing ecological hydrological functions. To this end, from July 2022 to October 2023, we conducted a comparative experiment simulating seasonal drought on 15-year-old C. lanceolata. We assessed the embolism resistance of C. lanceolata by constructing vulnerability curves and analyzed its water use patterns using hydrogen and oxygen isotope compositions. The research findings indicate that in October 2022, the hydraulic safety margin (HSM₅₀) of C. lanceolata increased from 0.99 ± 0.23 MPa to 1.12 ± 0.13 MPa under water input exclusion, suggesting that C. lanceolata can enhance its xylem embolism resistance to counteract short-term drought stress. Despite the ability of C. lanceolata to adjust its root distribution, C. lanceolata primarily relies on shallow soil moisture for survival, with the maximum water uptake from the 0–10 cm soil layer reaching up to 53.0 %±9.0 %. This mismatch between the tree’s water use pattern and soil moisture dynamics exacerbates drought stress during the dry season, leading to irreversible embolism accumulation over prolonged seasonal droughts. During the 2023 dry season, the natural percentage loss of conductivity (NPLC) in C. lanceolata trees from both the drought and control groups significantly increased to 27.45 ± 1.03 % and 19.60 ± 1.05 %, respectively, both higher than in the 2022 dry season (increases of 8.06 ± 3.01 % and 8.58 ± 2.36 %, respectively). Therefore, we believe that HSM can only assess a plant’s short-term resistance to sudden drought but cannot accurately determine its long-term adaptability to repeated extreme drought stress. A comprehensive assessment should be made by considering both the tree’s water use patterns and hydraulic characteristics.