Taiwan Forestry Research InstituteTaiwan Forestry Research Institute

Yau-Lun Kuo, Tien-Yun Li

2023

drought-tolerant classes, gas exchange function, shade tolerance, water potential when photosynthesis has ceased, water potential at the turgor loss point

The purposes of this research were to categorize the drought-tolerant classes of subtropical tree species in Taiwan using 2 physiological drought tolerance indices, and to explore the relationship between drought tolerance and shade tolerance for native Taiwan tree species. We used pressure- volume curves to calculate the leaf water potential at the turgor loss point (π_tlp) in 55 species of mature trees to represent leaf drought tolerance. We also applied long-term drought treatments to 47 species of seedlings and measured their predawn leaf water potential when photosynthesis had ceased (Ψ_A0) to represent the drought tolerance of the whole plant. Results showed that π_tlp values of mature trees ranged -2.29~-2.79 MPa, and Ψ_A0 values of seedlings ranged -3.29~-7.11 MPa. Tree species along the ridge of the Kenting karst forest showed lower values for both indices than trees growing in non-ridge habitats. Integrating results of this research with previously published data, we found that 124 subtropical tree species in Taiwan had π_tlp values of -2.03~-2.98 MPa and 86 species had ΨA0 values of -2.31~-7.93 MPa. Among these, 84 species of seedlings had Ψ_A0 values lower than the π_tlp values of their mature tree form, indicating that most species can maintain gas exchange function when losing turgor pressure. It was also found that the Ψ_A0 of seedlings and the π_tlp of mature trees had positive and significant relationships. However, no relationships were found of leaf drought tolerance or whole-plant drought tolerance with shade tolerance. Five levels of shade-tolerant species all showed a wide range of drought tolerance. We used Ψ_A0 to classify the 86 species into 3 drought-tolerant classes, and then used π_tlp to further classify these into subclasses. Seventeen species, including Planchonella obovata, Hibiscus tiliaceus, Acacia confusa, Lithocarpus konishii, and others, were classified into the highest drought tolerance level (I-a). Nine species, including Cinnamomum camphora var. camphora, Bischofia javanica, Cinnamomum kotoense, and others, were classified into the lowest drought tolerance level (III-c). Knowledge of the drought tolerance of native Taiwan woody species can provide essential guidance in choosing appropriate species for silviculture and ecological restoration efforts.