Variation Characteristics Of Cold Tolerance Of Erigeron Annuus And Conyza Canadensis Along Latitudinal And Altitudinal Gradients

Under the background of climate change,the geographical distribution pattern and dynamics of plants have always been one of the hot issues of ecology.Although current research generally believes that low temperature stress is the most important ecological factor that limits the plant latitude and altitude distribution,its limited physiological and ecological mechanism is not clear,so it is impossible to accurately explain the expansion or contraction of plant distribution under climate warming.Revealing the physiological and ecological mechanism and evolution characteristics of plants adapting to low temperature is the primary issue to understand the response of vegetation distribution patterns to climate change and predict population migration.In this study,we used the widely distributed species of invasive plants Erigeron annuus and Conyza canadensis at different latitudes and altitudes in China as research materials,replacing common species such as forest trees and trees to serve traditional ecological and the time and space scales involved in evolutionary biology.Using methods such as growth chamber cultivation,low temperature treatment and extreme cold event simulation,the characteristics of freezing tolerance gradual change of plant materials at different latitudes and altitudes were analyzed,and the mechanism of freezing tolerance in the geographical distribution and expansion of plants in different evolutionary backgrounds was discussed.The main conclusions are as follows:(1)With the increase of latitude,the supercooling point and freezing point of Erigeron annuus and Conyza canadensis had a tendency to decrease,indicating that the changes of supercooling point and freezing point of the two plants were related to the latitude.Under normal temperature conditions,the supercooling point and freezing point of Erigeron annuus were higher than that of Conyza canadensis,but after low-temperature acclimatization,Erigeron annuus was lower than Conyza canadensis.Therefore,the low-temperature sensitivity of the invasive species of Erigeron annuus was stronger than that of Conyza canadensis and it had stronger adaptability after low-temperature domestication,and can quickly adjust to enhance cold tolerance to cope with low-temperature stress.It may continue to spread to the colder areas in the north trend.The minimum temperature at the sampling point was also a climatic factor that affects the supercooling point and freezing point of the two plants.With the increase of altitude,the supercooling point and freezing point of plants decreased significantly,but after low temperature domestication treatment,the supercooling point and freezing point of low altitude plants were significantly higher than those of high altitude areas.This shows that plants at low altitudes are more sensitive to low temperatures than plants at high altitudes.Plants in low altitudes have the ability to quickly adapt to low temperature environments.By quickly adjusting the cold resistance mechanism,they were more adaptable to low temperature environments and have significantly improved cold tolerance.(2)With the increase of latitude,the degree of cell membrane damage of plants did not change significantly after normal temperature and domestication treatment,but after low temperature domestication treatment,the degree of cell membrane damaged of Erigeron annuus decreased,while the degree of cell membrane damage of Conyza canadensis did not occur the change indicates that the cell membrane system of Erigeron annuus was more capable of adapting to the cold environment.(3)With the increase of latitude,the damage degree of the photosynthetic system of the plants after normal temperature and domestication did not change significantly,but after low-temperature domestication treatment,the damage degree of the photosynthetic system of Conyza canadensis decreased slightly,while the damage degree of the photosynthetic system of Erigeron annuus was no change,which indicates that the photosynthetic system of Conyza canadensis was more capable of adapting to the cold environment.With the increase of latitude,the low-temperature sensitivity of the two plants has increased,and there is no significant change in the cell membrane system and photosynthetic system.With the increase of altitude,the low-temperature sensitivity of Conyza canadensis also increased;The low temperature sensitivity and cell membrane system's cold resistance of Erigeron annuus is stronger than that of Conyza canadensis,and the cold resistance of photosynthetic system is weaker than Conyza canadensis.The latitude and minimum temperature of the sampling point affect the plant's low temperature sensitivity,the annual average temperature affects the plant's photosynthetic system's cold tolerance,and the plant cell membrane system's cold tolerance has not been investigated.