Effects Of Different Irrigation Amounts On Photosynthetic Physiological Characteristics Of Populus Euphratica In Middle Age Forest

Populus euphratica has the biological and ecological characteristics of water,sunshine,salt and barren tolerance.In semi-desert and desert areas,Populus euphratica forest does not depend on meteoric precipitation,but on floods of rivers and infiltrated groundwater to survive.Populus euphratica forest is a riparian forest in arid desert area.It is of great theoretical and practical significance to study its ecological characteristics.There have been many studies on Photosynthesis and water physiological characteristics of Populus euphratica.In this study,Populus euphratica in Tarim River Basin of Xinjiang was taken as the research object,and the middle-aged forest Populus euphratica was irrigated in the field.Gas exchange parameters of Populus euphratica were measured by an open gas exchange LI-6400 portable photosynthesis system,and soil moisture changes under different irrigation amounts were measured by soil three-parameter apparatus.Light and diurnal variation,diurnal variation of water use efficiency,light response parameters and photosynthesis-CO₂response curve of Populus euphratica under different irrigation amounts were analyzed.The changes of gas parameters of Populus euphratica under different irrigation amount were compared,and the response of Photosynthetic Physiological Indexes of Populus euphratica to irrigation amount was discussed.The results show that:（1）The growth of Populus euphratica increased to a certain extent under different irrigation amounts,indicating that the amount of irrigation is related to the growth of Populus euphratica.（2）The transpiration rate,intercellular CO₂concentration,stomatal conductance,stomatal limit value and photosynthetic utilization efficiency of 11-year-old Populuseuphratica reached the maximum under 45 Kg·株^-1·次^-1irrigation.The transpiration rate,intercellular CO₂concentration,stomatal conductance,stomatal limitation value and photosynthetic efficiency of 15-year and 20-year-old Populus euphratica reached the maximum under 50 Kg·株^-1·次^-1irrigation.（3）With the increase of irrigation amount,the initial carboxylation efficiency,photosynthetic capacity and photorespiration rate of Populus euphratica leaves increased.The initial carboxylation efficiency and photosynthetic capacity increased by 35.48%,19.43,1.16%and 9.04%,12.03%and 6.59%under 40 Kg·株^-1·次^-1,45 Kg·株^-1·次^-1and 50 Kg·株^-1·次^-1irrigation compared with those without irrigation.The results showed that the photosynthetic electron transfer and phosphorylation activity,Rubisco activity,CO₂assimilation ability and utilization efficiency of Populus euphratica increased with the increase of irrigation amount.（4）The light saturation point,apparent quantum efficiency and maximum net photosynthetic rate of Populus euphratica varied greatly with different irrigation amount.With the increase of irrigation amount,the maximum net photosynthetic rate increased by 0.66%,1.03%and 1.07%compared with that before irrigation.The difference between LSP and LCP of 11-year-old Populus euphratica was the greatest under 45 Kg·株^-1·次^-1irrigation,and the difference between LSP and LCP of 15-year-old Populus euphratica and 20-year-old Populus euphratica was the greatest under 50 Kg·株^-1·次^-1irrigation.（5）Except for the irregular fluctuation of WUE in 20-year-old Populus euphratica forest,the water use efficiency of the other two-year-old Populus euphratica forests is"double peak"type under different irrigation amount.Generally speaking,the water use efficiency of Populus euphratica is 15 years>20 years>11 years,and the relationship betwen the amount of irrigation and the water use efficiency of Populus euphratica is not obvious.In summary:The suitable irrigation amount for growth of 11-year-old Populus euphratica was 45 Kg·株^-1·次^-1,and 50 Kg·株^-1·次^-1for 15-year-old and 20-year-old Populus euphratica.