Effects Of Water Stress On Photosynthetic Physiological Characteristics And Quality Of Alfalfa To Water Stress

For a long time,drought has affected the development of forage industry to a great extent.In recent years,drought has become a major obstacle to the healthy and sustainable development of modern agriculture due to many reasons such as warmer climate,lack of water resources and environmental deterioration.In order to obtain high quality,high yield and water-saving technology of Alfalfa in Hexi Desert irrigation area of Gansu Province,which has typical desert climate characteristics,gannong No.3 alfalfa was used as the experimental material in the ground Under irrigation mode,the method of artificial control of soil water was adopted to control the water content of Alfalfa（the percentage of soil water content in the field water capacity）by 75%⁸5%（CK:full irrigation）,65%⁷5%（LD:light water stress）,55%⁶5%（MD:moderate water stress）,45%⁵5%（SD:heavy water stress）.The alfalfa under different water stress was analyzed The photosynthetic characteristics,chlorophyll fluorescence parameters,aboveground biomass and nutritional quality of alfalfa were studied.The effects of water stress on the physiological and ecological indexes of alfalfa were studied.The optimal water control model for alfalfa growth in desert irrigation area was obtained.The main conclusions are as follows:（1）With the intensification of water stress,the net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）,and stomatal limit value（Ls）of the first three crops of alfalfa gradually decreased,and their intercellular CO₂concentration（Ci）It gradually decreases under mild water stress and increases under moderate and severe water stress.The maximum LD is when the water use efficiency reaches its peak.The Pn,Gs and Tr of the fourth stubble alfalfa gradually decreased with the intensification of water stress,Ci gradually decreased under mild and moderate water stress,increased under severe water stress,and Ls under mild and moderate water stress It gradually increased under stress and decreased under severe water stress.WUE reached its peak around 14:00,and the differences between water treatments were not significant.The results showed that there were both stomatal and non stomatal factors in Pn reduction of Alfalfa under water stress.Stomatal restriction was the main factor in the first three crops under light water stress,non stomatal restriction was the main factor in moderate and severe water stress,stomatal restriction was the main factor in the fourth crop under light and moderate water stress,and non stomatal restriction was the main factor in severe water stress.（2）Environmental factors are important factors that affect the photosynthesis of alfalfa leaves.The main factors that affect the daily changes in the net photosynthetic rate of alfalfa in the first and third crops through correlation analysis are stomatal conductance,transpiration rate,and photosynthetic effective radiation.The main factors of diurnal change of net photosynthetic rate of the second crop of alfalfa are stomatal conductance and transpiration rate.The main factors that affect the diurnal change of net photosynthetic rate of the fourth crop of alfalfa are photosynthetic effective radiation.（3）With the intensification of water stress,the Chla,Chl（a+b）and Chla/b of the four stubble alfalfa first increased and then decreased,with the largest under mild water stress,and the values were 1.65,2.04,4.15,1.44,1.79,4.03,1.19,1.50,3.89,0.9,1.27,3.42;Chlb is the largest under full irrigation,and its values are 0.44,0.40,0.35,0.29 in order,and gradually decreases with the increase of water stress.There was no significant difference between the four stubble alfalfa under mild water stress and Chla and Chl（a+b）under full irrigation,indicating that light water stress can increase the efficiency of light energy use.（4）With the intensification of water stress,the initial fluorescence（Fo）of the four-alfalfa alfalfa basically showed an increasing trend,the maximum fluorescence（Fm）,variable fluorescence（Fv）,PSII primary light energy conversion efficiency（Fv/Fm）And PSⅡpotential activity（Fv/Fo）decreased significantly;the photochemical quenching coefficient（qP）and the actual photochemical efficiency（ΦPSⅡ）decreased significantly with the increase of water stress in the first three crops,but not in the fourth crop;The apparent electron transfer rate（ETR）showed a downward trend with the intensification of water stress,but the decline in the first crop was larger,and the decline in the latter three crops was smaller;the non-photochemical quenching coefficient（NPQ）increased with water stress.The increase is smaller.Under mild water stress,the decrease in Fv/Fm,Fv/Fo,ΦPSⅡ,and ETR of alfalfa was smaller,indicating that the light system injury of the leaves was lighter under mild water stress.（5）The plant height,stem diameter and hay yield of four alfalfa stubbles were the highest under full irrigation,and the values were 100cm,3.73 mm,5718 kg·hm^-2,87 cm,3.57 mm,3759 kg·hm^-2,76 cm,3.13 mm,3241 kg·hm^-2,39 cm,2.36 mm,2354 kg·hm^-22 in turn according to the stubble times,but the yield of four alfalfa stubbles decreased with the aggravation of water stress There was no significant difference between LD and CK,which indicated that the water-saving and stable yield could be achieved under mild water stress.6)In the same stubble,under different water treatments,the crude protein content and relative feeding value of Alfalfa under LD were the highest,which were20.67%,139.68,19.24%,144.95,18.06%,160.42,21.20%,199.28,respectively.The crude protein content of the first three stubbles was significantly different from that of the control,but the fourth stubble was not significantly different;the content of neutral detergent fiber and acid detergent fiber is the smallest,and their values are41.94%,33.28%,42.83%,28.45%,38.75%,28.34%,32.79%,23.95%,the four stubble were significantly different from the control;the four stubble alfalfa had no significant difference in crude ash content under mild water stress and CK;under mild water stress The increase in protein content and the decrease in the content of neutral detergent fiber and acid detergent fiber indicate that proper water stress can improve the nutritional quality of alfalfa.