Effect Of Different Irrigation Amount On Photosynthetic Physiology Of Young Populus Euphratica

The shortage of water resources is the most important factor restricting the production and development of agroforestry in arid and semi-arid areas of northern China.The amount of soil moisture content will affect the photosynthesis of plants,thus affecting the growth and distribution of plants.In order to investigate the effect of different irrigation amount on the photosynthetic physiological indexes of young forest age poplar,the dynamic changes,light response process and CO2 response process of 3 different age forest poplar under different irrigation quantities were determined by Li-6400 photosynthetic instrument,which was used as the test object for 3 years,5 years and 7 years.To determine the appropriate amount of irrigation for3 different age forest poplar.The results show that:（1）The results were as follows:（1）the diurnal variation of P_n,Cond,C_i,T_r,WUE of Populus euphratica at 3,5 and 7 years old had obvious changes under different irrigation volume.The daily mean value of Pn of 3-year-old Populus euphratica reached the maximum under T2 treatment(29 kg·plant^-1·times).It was 20.1μmol·m^-2·s^-1,which was higher than that before irrigation（34.19%）.The Pn of 5-year-old and7-year-old Populus euphratica reached the maximum under T3 treatment(38 kg·plant^-1 time),which were 14.06μmol·m^-2·s^-1and 14.6μmol·m^-2·s^-1,respectively,higher than26.48%and 28.38%.（2）The WUE of Populus euphratica at 3,5 and 7 years old showed a tendency of high in the morning and low in the afternoon,and the peak value appeared at 6:00or 8:00 in the morning.Among them,3-year-old Populus euphratica reached the maximum value at T2 treatment(29 kg·plant^-1 time),the daily average of WUE was1.62μmol·mmol^-1;The daily mean of 5-year-old and 7-year-old Populus euphratica reached the maximum at T3 treatment(38 kg·plant^-1 time),and the peak values were1.93μmol·mmol^-1.and 2.22μmol·mmol^-1.respectively.Under different irrigation conditions,the transpiration rate increased with the increase of PAR and T_a.However,the time of peak value appeared inconsistencies due to the influence of irrigation volume,all of which appeared at 12:00、14:00 and 16:00.（3）In combination with the relationship between P_n diurnal variation and L_sand C_i of Populus euphratica at 3 years old,5-year-old and 7-year-old Populus euphratica showed that the decrease of Pn at noon was mainly affected by stomatal limitation.The decline in Pn in the afternoon was mainly due to non-stomatal constraints.（4）The light response of 3,5and 7-year-old Populus euphratica showed that P_nincreased with the increase of PAR,and P_nmax increased with the increase of irrigation quantity.3-year-old Populus euphratica Pnmax was the largest in T2 treatment(29kg·plant^-1).23.58μmol·m^-2·s^-1;The maximum values of P_nmax of 5-year-old and 7-year-old Populus euphratica were 34.77 and 29.45μmol·m^-2·s^-1,both appeared in T3treatment(38kg·strain^-1·times).The young forest of Populus euphratica showed high LSP and low LCP,indicating that they had strong adaptive energy to light.（5）Using the right-angle hyperbolic model,the non-right-angle hyperbolic model,the right-angle hyperbolic modified model and the exponential model for 3-year-old,The simulation results of light response data of 5-year-old and 7-year-old Populus euphratica seedlings were significantly different under different irrigation volume.Among them,the fitting value of the right angle hyperbolic correction model is the most close to the measured value,and the fitting effect is the best.（6）The CO₂ response curve of 3,5 and 7 year-old Populus euphratica showed an upward trend with the increase of irrigation quantity,and the A_maxincreased with the increase of irrigation volume,mostly in 35μmol·m^-2·s^-1.It has strong photosynthetic ability.（7）The CO₂ response data of 3-year-old,5-year-old and 7-year-old Populus euphratica were simulated by right-angle hyperbolic model,non-right-angle hyperbolic model,right-angle hyperbolic modified model and exponential model.Comprehensive comparison of fitting results,right-angle hyperbolic correction model>exponential model>non-right-angle hyperbolic model>right-angle hyperbolic model.