To investigate the photosynthetic characteristics and leaf anatomical structures of seedlings from the endangered plants Ormosia olivacea, Ormosia pachycarpa, and Ormosia sericeolucida, this study aimed to elucidate the influence of leaf structure on photosynthetic traits and light requirements among these three Ormosia species, thereby providing reference for their introduction and cultivation. This study measured the light response curves, CO₂ response curves, leaf epidermal and anatomical characteristics, and photosynthetic pigment content of the three Ormosia species. Results indicate: 1. All three species exhibit photophilic tendencies, with Ormosia olivacea demonstrating the highest photosynthetic capacity, achieving a maximum net photosynthetic rate (Pmax) of 1.9062 mol m⁻² s⁻¹. Ormosia pachycarpa exhibited the highest potential maximum net photosynthetic rate (Amax), demonstrating superior CO₂ utilisation capacity. The Amax values for all three species were significantly higher than their Pmax values. 2. Among the three Ormosia species, Ormosia sericeolucida exhibited the thickest leaf structure, with palisade tissue thickness ordered as follows: Ormosia sericeolucida > Ormosia pachycarpa > Ormosia olivacea. 3. Stomata were present on the lower epidermis of all three species. Ormosia sericeolucida possessed the largest individual stomatal area, while Ormosia olivacea exhibited the highest stomatal density. 4. The chlorophyll a content (Chl a) of all three Ormosia species exceeded their chlorophyll b content (Chl b), indicating they are photophilic plants. Ormosia sericeolucida exhibited higher chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chl) contents than both Ormosia olivacea and Ormosia pachycarpa. Ormosia olivacea possessed the highest carotenoid content (Car). In summary, Ormosia pachycarpa exhibited the highest potential maximum net photosynthetic rate (Amax), demonstrating the strongest CO₂ utilisation capacity, followed by Ormosia olivacea, with Ormosia sericeolucida showing the lowest. Appropriately increasing CO₂ levels in cultivation sites would benefit photosynthesis and material accumulation in all three Ormosia species, promoting robust growth.

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 (δ¹³$C$) 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 (δ¹³$C$) 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 (δ¹³$C$) 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 (δ¹³$C$) 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 (δ¹³$C$) 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.

To investigate the rationality of water-use efficiency in agroforestry systems within this region, this study utilised the medicinal and edible plant Sophora japonica cv.jinhuai as a foundation. Five mixed planting models were established, incorporating Ardisia gigantifolia, Melicope pteleifolia, Camellia limonia, Belamcanda chinensis, Isatidis radix, and Pilea basicordata. Water-use efficiency (WUE) was analysed by measuring the carbon-stable isotope composition (δ¹³C) of plant leaves. Compared to previous studies that primarily focused on δ¹³C in single species or simple composite systems, this research innovatively evaluates the water-use efficiency (WUE) performance of different composite patterns and their impact on system stability at both the species and system levels, integrating the theory of fitness differentiation. Results indicate that the ranges of δ¹³C and WUE for the five mixed cropping systems were −27.0633‰ to 31.2188‰ and 27.7191 to 50.0365 μmol/mol, respectively. WUE ranking was: Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) > Sophora japonica cv.jinhuai—Camellia limonia (SC) > Sophora japonica cv.jinhuai—Belamcanda chinensis + Isatidis radix (SBI) > Sophora japonica cv.jinhuai—Melicope pteleifolia (SM) > Sophora japonica cv.jinhuai—Ardisia gigantifolia (SA). At the species level, the Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) composite planting model is better suited to karst arid environments, while the Sophora japonica cv.jinhuai—Ardisia gigantifolia (SA) composite planting model exhibits lower overall plant water-use efficiency (WUE) and weaker drought resistance. At the system level, Sophora japonica cv. jinhuai exhibited significantly higher water-use efficiency (WUE) than understory medicinal plants in most composite patterns, with pronounced differences in species fitness and poor system stability. The Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) model exhibited the highest WUE. Furthermore, no significant difference in WUE was observed between Sophora japonica cv.jinhuai and Pilea basicordata, indicating relatively high fitness matching and good coordination in water use. These species can coexist stably, suggesting promising application potential in karst arid environments. Therefore, this study not only evaluated the water-use performance of each species within the composite model but also identified SCP as the most suitable agroforestry configuration for karst regions from a system stability perspective. This provides a scientifically grounded basis for optimising agroforestry practices in these areas, integrating both species-level and system-level perspectives. It should be clarified that the WUE calculated based on δ¹³C in this study is a relative indicator rather than an absolute physiological measurement. Its reliability depends on the core assumptions and parameter settings of the isotope model.

Malania oleifera, the sole species of its genus, is an endangered tree endemic to the karst regions of China and a valuable woody oil crop. However, deep seed dormancy and slow germination severely limit its propagation and utilization. In this study, freshly harvested mature seeds of M. oleifera were soaked in gibberellic acid (GA₃) solutions at different concentrations. Germination traits and physiological and biochemical parameters were assessed, and transcriptome sequencing was performed to investigate the mechanisms underlying GA₃-promoted seed germination. Soaking seeds in GA₃ for 24 h significantly promoted germination in a concentration-dependent manner. The strongest response occurred at 600 mg·L⁻¹ GA₃, with germination potential and germination percentage reaching 34.2% and 60.0%, respectively. The beneficial effect declined at 800 mg·L⁻¹. Treatment with 600 mg·L⁻¹ GA₃ significantly increased superoxide dismutase (SOD) and peroxidase (POD) activities and reduced malondialdehyde (MDA) content, indicating that an appropriate GA₃ concentration helped maintain redox balance during germination. Transcriptome analysis identified 7548 and 3571 differentially expressed genes in UT_vs_W24 and W24_vs_GA24, respectively. These results indicated that water soaking initiated germination-related transcriptional changes that were further modified by GA₃ treatment. Functional enrichment analysis showed that transcriptional changes induced by water soaking mainly involved carbohydrate and lipid metabolism, secondary metabolism, and responses to stimuli, whereas GA₃ treatment further modulated redox processes, defense responses, plant hormone signal transduction, and the mitogen-activated protein kinase (MAPK) signaling pathway. Reconstruction of the plant hormone and MAPK signaling pathways showed that GA₃ markedly affected the expression of genes involved in gibberellin, abscisic acid, auxin, and brassinosteroid signaling. GA₃ also regulated the MKK–MPK cascade and downstream transcription factors, including WRKYs. Together, these findings characterize the physiological responses of M. oleifera seeds to GA₃ and reveal the molecular mechanisms underlying GA₃-promoted germination, providing a basis for improving the propagation efficiency of this valuable species.