Tree Genetics and Molecular Breeding 2025, Vol.15, No.5, 211-219 http://genbreedpublisher.com/index.php/tgmb 213 3 Stress Factors Affecting M. glyptostroboides 3.1 Abiotic stresses: drought, salinity, temperature extremes, flooding Drought and salinization can slow down plant growth, damage leaves, and also affect photosynthesis and water use efficiency. Research has found that whether it is drought or salinization alone, or both occurring together, they will significantly inhibit the growth and physiological activity of Metasequoia glyptostroboides seedlings. However, if some synthetic or natural super absorbent polymers, such as konjac glucomannan, are added to the soil, this pressure can be effectively alleviated, helping plants improve stress resistance and better growth performance (Li et al., 2018; Kong et al., 2022). Extreme temperatures also have a significant impact on the seed germination and seedling survival of Metasequoia glyptostroboides. The germination rate will significantly decrease at both 5°C and 35°C. Fan et al. (2020) hold that spring drought will significantly reduce the survival rate of seedlings, which is the main factor restricting the natural distribution and renewal of Metasequoia glyptostroboides. Metasequoia glyptostroboides has a certain adaptability in waterlogging conditions. Yang et al. (2019) demonstrated in their research that its fine roots can undergo significant structural changes, such as the formation of cortical ventilation tissue or lignification and thickening, which is beneficial for its adaptation to both aquatic and terrestrial environments. 3.2 Biotic stresses: pests and diseases In its native habitat and artificial forests, Metasequoia glyptostroboides is also threatened by various pathogenic fungi. Studies have shown that the combined infection of pathogens such as Fusarium spp., Neocosmospora spp. and Phytophthora acerina is an important cause of metasalopecia glyptostroboides decline and death. This kind of disease is particularly serious in the protective forests of the Yangtze River Basin. If multiple pathogenic bacteria occur simultaneously, the severity of the disease will be more severe, which will have a significant impact on the growth and ecological functions of Metasequoia glyptostroboides (Liu et al., 2024). In addition, the litter of Metasequoia glyptostroboides forests has a self-toxic effect, which can inhibit seed germination and seedling growth and hinder natural renewal (Xu et al., 2022). 3.3 Climate change implications for survival and adaptation Climate warming and human activities have also led to the continuous shrinking and migration of the suitable areas for Metasequoia glyptostroboides. Over the past 50 years, the average annual temperature and extreme temperature in the distribution area of Metasequoia glyptostroboides have increased significantly. The area of the suitable zone has decreased at a rate of approximately 370.8 km2 per decade, and the altitude range of the distribution has gradually declined (Zhao et al., 2020). Future climate model predictions show that precipitation in dry months, diurnal temperature differences, and human activity footprints are the main factors determining the expansion or contraction of Metasequoia glyptostroboides habitats (Li et al., 2025b). Climate warming has also altered the phenological period of Metasequoia glyptostroboides, advancing and prolonging the growing season. However, it has also continued to compress the suitable growth area, intensifying the risk of endangerment (Zhao et al., 2020). The superimposition of climate change and habitat fragmentation has made the degradation and renewal obstacles of Metasequoia glyptostuca populations even more serious (Tang et al., 2011; Li et al., 2025b). 4 Traditional Breeding Approaches for Stress Tolerance 4.1 Germplasm collection and selection of superior individuals The collection of germplasm resources and the assessment of genetic diversity are the basis for Metasequoia glyptostroboides’ stress-resistant breeding. Li et al. (2025a) demonstrated that after introduction, the population had a relatively high genetic diversity at the species level (He = 0.640), with little difference between the mother trees and the seedlings. This indicates that there are still many excellent genotypes available for utilization in the population, which is helpful for the screening and improvement of stress resistance traits. Chen et al. (2020) found that the parents of Metasequoia glyptostroboides exhibit strong trait plasticity in different environments. For instance, leaf area and dry weight vary with environmental and human disturbances. These differences provide a basis for selecting individuals with strong stress resistance.
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