Response Of Shelterbelt Plants To Saline Drip Irrigation And Optimization Of Irrigation Scheduling In The Taklimakan Desert

Artificial vegetation planting is an internationally widely adopted measure to rebuild the ecology of sand areas and prevent sand damage.Water is the key factor affecting the structural stability and maintaining normal function of the desert ecosystem,and is also the biggest limiting factor restricting vegetation growth.Transpiration is the main pathway of water dissipation in plants,which participates in and influences the material cycle and energy flow of the ecosystem,and is influenced by environmental factors.Photosynthesis,as a basic unit of physiological metabolism and material accumulation,is sensitive to changes in the external environment and is an important link in the analysis of plant growth and metabolic response to the environment.In order to better explain the effects of saline water drip irrigation on plant physiology of Taklamakan Desert Highway shelterbelt,and to explore the feasibility of water-saving irrigation in the shelterbelt,three irrigation amount（W1=17.5 mm,W2=25 mm,W3=35 mm）and three irrigation cycles（F1=10 d,F2=20 d,F3=40 d）（9 treatments in total）were applied in this study by field control experiments.Finally,the optimal irrigation measures were obtained for the Mongolian calligonum（C.）and Haloxylon mmodendron（H.）were derived using a fuzzy integrated evaluation model.The main conclusions were as follows:（1）The characteristics of moisture dynamics under different irrigation treatments were revealed,and the effects of different irrigation treatments on soil moisture in the shelterbelt were clarified.Under saline water drip irrigation,the soil moisture infiltration depth was 50-60 cm under W1 and W2 irrigation,while it was 100 cm under W3 irrigation.0-100 cm soil moisture content showed a cubic polynomial relationship with the number of days after irrigation during the irrigation cycle.The soil moisture changed in 0-60 cm layer after irrigation can be divided into a rapid decline（1-9 d）,a slow decline（9-19 d）,and a relatively stable period（19-39 d）,and were closely related to the initial soil moisture content;soil moisture in the soil layer below 60 cm changed slowly after irrigation.Therefore,under the same total amount of irrigation,increasing the amount of single irrigation and extending the irrigation cycle can make the irrigation water infiltrate into the deep soil,reduce ineffective evaporation,and facilitate soil moisture storage.The net depletion period of soil water was from May to July,and the net recharge period of soil water was from July to September.Only under the W3 irrigation amount,the shallow and deep soil water storage have increased.（2）The characteristics of stem flow of shelterbelt under different irrigation treatments were explored to reveal the effect of drought stress on stem flow of shelterbelt.With the increase of irrigation amount,the midday peak time of stem flow of C.was prolonged,the peak time of stem flow of H.was advanced,and the daily cumulative stem flow of both plants increased.At the same irrigation rate,the cumulative daily stem flow was greatest at 20 d irrigation cycle.The correlation between branch stem flow and soil moisture content of the plant water absorption layer was greater for both plants.There was a certain time lag between stem flow and environmental factors for both plant species,with correlation was solar radiation>temperature>relative humidity>saturation water vapor pressure.Using the real-time monitoring data of solar radiation,air temperature,relative humidity,wind speed,soil water content and soil temperature as well as plant phenology indicators,the BP-neural network was used to fit the stem flow of the two plants,and the R²of the fitted curves were all greater than 0.96,and BP-neural network could be used to estimate and predict the stem flow of plants.（3）The photosynthetic characteristics of shelterbelt under different irrigation treatments were investigated to reveal the effects of drought stress on the photosynthetic characteristics of shelterbelt.The P_ndaily mean of C.under W3 was 20.68±7.60μmol CO₂m^-2s^-1,it under W2 was21.70%lower than that of W3,but under W1 was 0.10%higher than that of W3.The T_rdaily mean of C.under W3 was 9.78±1.57 mmol H₂O m^-2s^-1,decreased by 26.89%under W2 and increased by 0.09%under W1.The P_ndaily mean of H.under W3 was 8.97±2.00μmol CO₂m^-2s^-1,under W2 and W1 were 30.71%and 0.03%lower than that of W3respectively.The T_rdaily mean of H.under W3 was 9.78±1.57 mmol H₂O m^-2s^-1,which decreased by 44.02%under W2 and 18.96%under W1.The net photosynthetic and transpiration rates of C.were higher than those of H..C.under W1 improved WUE mainly by increasing P_nin the morning and taking a midday rest through photosynthesis.H.adopted high transpiration at noon to avoid the damage to leaves caused by high temperature,which resulted in the decrease of WUE,the P_nand T_rof C.and H.decreased under W2,but the T_rdecreased more than P_n,to improve WUE.Water stress reduced LSP,LCP,R_dof C.and H.Plants’photosynthetic capacity was weakened while subjected to water stress and photo inhibition was more likely to occur.However,plants showed different performances in different seasons,and atmospheric RH has a particular compensation effect on soil water stress,which reduces the impact of soil water stress on plant photosynthesis.（4）Combining the soil water dynamics,the photosynthetic and stem flow characteristics of the shelterbelt under different irrigation treatments,by using a fuzzy integrated evaluation model,the feasibility of conservation irrigation of the shelterbelt in the Taklamakan Desert hinterland was clarified.The optimal irrigation treatment was W2F1（single irrigation volume of 25 mm,irrigation period of 10 d）for the C.,and that was W2F2（single irrigation volume of 25 mm,irrigation period of 20 d）for the H..In conclusion,the soil water in the shelterbelt in the Taklamakan Desert hinterland has a certain surplus for plant growth under the current irrigation measures,and under moderate water stress,the shelterbelt can improve water use efficiency through their photosynthesis and stem flow adjustment.Therefore,it is feasible to adopt water-saving irrigation measures in the Taklamakan Desert hinterland.This study can present some basic data and a theoretical basis for the development of water-saving irrigation measures in the Taklamakan Desert shelterbelt.