Comparative Study On Physiological And Ecological Characteristics Of Populus Euphratica Seedlings Propagated From Roots And Natural Seeds In The Middle And Lower Reaches Of Tarim River

In recent years,due to the sharp decline in river water volume,the lower reaches of the Tarimu River have been cut off,so that in the lower reaches of the Tarimu River Populus euphratica breeding,renewal appears obvious lag and even degradation.In order to increase,maintain and stabilize the local ecosystem,control desertification and improve the research content of artificial cultivation of Populus euphratica seedlings,analyze and compare different physiological and ecological characteristics of the growth of different seedlings under different breeding strategies in the middle and lower reaches of the Tarimu River.Under the breeding strategy,the growth volume and photolysal physiological characteristics of different seedlings are designed to explore the rationale of artificial breeding Populus euphratica seedlings,and to provide scientific basis for the cultivation and growth of Populus euphratica seedlings,methods and the popularization of artificial breeding Populus euphratica technology.In June/July/August 2019,Populus euphratica seedlings of different seedling ages under the two reproduction methods were used as experimental materials to obtain photolysal index data,growth index data,and to carry out comprehensive analysis.The results showed that:（1）There were obvious differences in photolysal day changes of different seedling ages under the two reproduction methods.Under the two reproduction methods,the threshold size and trend change of the photosynthetic diurnal parameters of Populus euphratica seedlings of different seedling ages under the two reproduction methods were different.Taking the net photosynthetic rate（Pn）as an example,the Populus euphratica seedlings under the root reproduction method mainly had a bimodal trend,while the Populus euphratica seedlings had a single-peak trend under the seed germination method.However,whether it was root reproduction method or seed germination method,5 and 7 years Populus euphratica seedlings had better ability to carry out photoalysing,performance of high-gloss,high steaming,high water utilization efficiency.Under the two reproduction methods,the photosynthetically active radiation（PAR）in the ecological environment parameters of the net photosynthetic rate（Pn）of Populus euphratica seedlings had an obvious limiting effect.Among the physiological parameters,the intercellular CO₂concentration（Ci）and stomata limit value（Ls）had a profound effect on the net photosynthetic rate（Pn）of Populus euphratica seedlings.（2）There were significant differences in the photolycerative-CO₂ response characteristics of different seedlings under different reproduction modes.Using the right-angled bi-curve correction model to fit the CO₂ response curve of different seedlings of different seedling age under the two reproduction methods,it was found that the three Populus euphratica seedlings under the two reproduction methods had higher maximum net photolytic rate（Pnmax）,initial sterilization efficiency（CE）,saturation CO₂ concentration and respiratory rate（Rp）and lower CO₂ compensation points than seed germination method.The Populus euphratica seedlings under root reproduction method had stronger photolysaling ability and can fully adapt to the environment of high CO₂ and low CO₂ concentration.However,Populus euphratica seedlings under the seed germination method can not make better use of the environment of high CO₂ and low CO₂ concentration,higher and lower CO₂ concentration can be carried out by plant leaves for photocodying and prevent photolysal rate increase.（3）There were obvious differences in photolysal-light response characteristics of different seedlings under different reproduction methods.Using the right-angled bi-curve correction model to fit the photo-light response curve of different seedlings of different seedling age under the two reproduction methods,it was found that the seedlings of each seedling age showed high surface quantum efficiency,high maximum net photoresort rate,high light saturation point,low light compensation point and high dark breathing rate compared with the seed germination method.Under the two reproduction methods,3-year-old root seedlings（July）and 7-year-old seedlings（August）had excellent photosynthetic potential.The 5-year-old rooting seedlings（July）and the 3-year-old seedlings（August）can perform better photosynthesis in the environment of high photosynthetically effective radiation.The5-year-rooted Populus euphratica seedlings（June）and the 7-year-old seedlings（August）had better transformation efficiency to low light intensity.（4）There are obvious differences in the growth characteristics of different seedlings under different reproduction methods.The growth of Populus euphratica seedlings under the two reproduction methods varied significantly throughout the growth season（P<0.05）.The7-year-old root seedlings and 3-year-old seedlings grew the fastest in height and ground diameter.The heiht growth of the root seedlings was mainly concentrated between June and July,while Seed germination reproduction seedlings were concentrated in July and August.The ground growth of the root seedlings was concentrated in July,and the seedlings of the seedlings were concentrated in August.On the whole,the tree height growth of root seedlings was slightly better than that of seedlings,and the ground diameter growth rate of seedlings was better than that of root seedlings.To sum up,root reproduction seedlings had certain advantages in ecological adaptability.In the process of plant restoration of Populus euphratica forest in the Tarim River Basin,proper and timely adoption of root reproduction methods will be more effective in helping the Populus euphratica forest to recover and renew.