Abstract

To investigate the long-term water use efficiency (WUE) and ecological adaptation strategies of seven endangered Ormosia plant species, and to identify superior tree species with strong drought resistance, thereby providing a scientific basis for ecological restoration, represented the objectives of this research. This study focused on Ormosia semicastrata, Ormosia pinnata, Ormosia fordiana, Ormosia xylocarpa, Ormosia glaberrima, Ormosia emarginata and Ormosia henryi. Using these seven Ormosia species as subjects of study, and the commonly planted afforestation species Michelia macclurei and Castanopsis hystrix as controls, we determined long-term water-use efficiency by measuring stable carbon isotope (δ13C) values of the leaves. This was combined with growth indices and chlorophyll content; a systematic analysis was conducted of interspecific differences and similarities with the afforestation species, to reveal the ecological adaptability and survival potential of Ormosia plants in arid environments. Methodologically, leaf carbon isotope (δ13C) values were measured for each tree species to estimate long-term water use efficiency, whilst growth indices and chlorophyll content were also determined to compare differences between Ormosia plants and the control species. The results indicate that the leaf carbon isotope (δ13C) values of the seven Ormosia species ranged from −31.88‰ to −29.03‰. Among these, O. xylocarpa, O. pinnata and O. emarginata exhibited higher leaf carbon isotope (δ13C) values and water use efficiency, suggesting greater water utilisation capacity and drought tolerance; whereas O. fordiana and O. glaberrima exhibited lower values for both parameters. Chlorophyll analysis revealed that the total chlorophyll content of O. pinnata and O. fordiana was significantly higher than that of Michelia macclurei and Castanopsis hystrix, and the chlorophyll a to chlorophyll b ratio of all Ormosia species was higher than that of the afforestation tree species, suggesting greater photosynthetic capacity and adaptability to high-light environments. Furthermore, leaf carbon isotope (δ13C) values showed a highly significant positive correlation with water use efficiency, validating the reliability of carbon isotopes in assessing long-term water use efficiency in plants. Taking all indicators into account, O. xylocarpa and O. pinnata demonstrated good root development and efficient allocation of photosynthetic pigments whilst maintaining high water use efficiency; they are therefore considered excellent tree species that combine drought resistance with growth potential. By integrating growth, photosynthetic and water-use characteristics, this study has clarified the water-adaptation strategies of different Ormosia species, providing a scientific basis for selecting drought-tolerant Ormosia species and for ecological restoration.

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