4.1 The influence of environmental factors on T. chinense’s distribution
Among the many environmental factors that affect the growth and development of T. chinense , only a few major environmental factors affect its distribution. Under the current climate conditions, water-related environmental factors (Bio18) have the highest impact on the distribution of T. chinense , which is basically consistent with the research of Gao et al. (P. Gao et al., 2023). T. chinense is mostly found in shaded or humid areas, and has poor drought resistance. If there is insufficient rainfall, its growth and development will be inhibited (Tang et al., 2021; Chinese botanical society, 1988). In the summer, excessive moisture in the soil or water on the surface can lead to root rot and hinder its growth (Tang et al., 2021; Yanar et al., 1997). In addition to precipitation, temperature also has an important impact on the distribution of T. chinense . Among them, Bio11 and Bio08 play an important role in the distribution of T. chinense . The suitable value range of Bio11 is wide (-26.47℃~ 13.22℃), and it could be seen that T. chinense has high cold resistance. In cold winter, in the process of overwintering and dormancy of T. chinense , starch may be degraded into soluble sugar mainly through starch phosphorylation to ensure that there are sufficient carbohydrates to maintain its growth and improve its stress resistance in low-temperature environment during dormancy, so that it can overwinter smoothly (Song et al., 2015). At the same time, the soluble sugar forms small molecular solutes under low-temperature stress, which further improves its ability to resist severe cold (Blasing et al., 2005). Bio08 represents the mean temperature of wettest quarter. The spatial and temporal distribution of precipitation in Asia is extremely uneven. There is more precipitation in summer, and the wettest quarter is mainly concentrated in summer (Zhan, 2013). When the summer temperature is greater than 30℃, seedling collapse occurs in theT. chinense . And the mortality rate of annual individual seedling collapse is relatively high, which is basically unable to survive (Song et al., 2015). This seriously affects the renewal of the T. chinense population and the continuation of its species. The range of Bio08 (9.08℃ ~ 26.38℃) well reflects this phenomenon (Luo & Guo, 2012).
By the 2090s, the Bio11 and Bio08 within the suitable area of T. chinense have risen by 6.32°C and 6.42°C, respectively. For high-latitude areas within the suitable area, the increased winter temperature may prevent T. chinense from entering its hibernation period, leading to continuous nutrient consumption and potentially adverse effects on the growth and reproductive capacity of the following year. For low-latitude areas in the suitable area, high temperatures may not only exacerbate the lodging of T. chinense , but also accelerate leaf senescence, reduce the reuptake rate of N and P, and weaken its ability to adapt to the environment (X. Li et al., 2023; Vergutz et al., 2012). Therefore, in a century of climate change, temperature increasing may be detrimental to the growth of T. chinense , reducing its ability to adapt to the environment and further threatening the population. By the end of this century, the Bio18 may increase to 438.51 mm. It is speculated that, with increasing summer precipitation, the negative effect of the single temperature factor (the increase in soil evaporation) on T. chinense may be counterbalanced by the increase in precipitation (the increase in soil moisture) to reach an equilibrium state. However, supposing there is further increase in precipitation or temperature, the balance may be disrupted, creating water or temperature stress. In that case, it may limit the growth of T. chinense .