Effects Of Regulation Deficit Irrigation During Canopy Development Stage On Source And Sink Characteristics Of Sugar Beet Under Drip Irrigation

【 Objective 】 In crop plants,the physiological basis of dry matter production is dependent on the source-sink theory,where the source is the potential capacity for photosynthesis and the sink is the potential capacity to utilize the photosynthetic products.High yield can only be achieved when the quantity and intensity of the crop’s source and sink reach coordination.How soil water content affects the formation and distribution of carbohydrate in source-sink organ of sugar beet is not clear.In this experiment,regulated deficit irrigation was conducted during the water sensitive period of sugar beet.The assimilate distribution was studied to clarify the source and sink relationship of regulated deficit irrigated sugar beet in arid land.【Methods】 In 2018 and 2019,Beta 356(Beta vulgaris L.)was used as the test material to set the field experiment of 70% field capacity(70% FC),50% field capacity(50% FC)and 30% field capacity(30% FC)respectively during canopy development stage,denoted as T1,T2,T3,after the end of canopy development stage,all treatments were supplied with water according to the control.The indexes of agronomic traits,lateral root distribution,non-structural carbohydrate content and key enzyme activities of sucrose metabolism were determined before and after water treatment.【Results 】(1)Under regulated deficit irrigation,the time reached maximal accumulation rate of dry matter(Tm)was delayed,the maximum accumulation rate(Vm)was decreased while the rapid accumulation period was increased.Compared with T1,the proportion of root dry matter increased while the proportion of above ground dry matter decreased,and the total amount of dry matter increased by 2.4%of T2 treatment.The total amount of dry matter decreased by 11.4% of T3 treatment and which mainly distributed in leaves.Compared with T1,sugar beet yield,sugar content and sugar yield increased by0.68%-8.3%,-3.8%-4.3% and 4.1-4.3% under T2 treatment,and sugar content increased by 2.5%-7.5%under T3 treatment in 2018 and 2019.(2)During regulated deficit irrigation in canopy development stage,the photosynthetic rate,leaf quantity,leaf area and leaf Chlb content decreased.After irrigation the values of Amax,Rd and LCP under T2 treatment were significantly higher than that of the control treatment during storage root development and sugar accumulation stage.It showed that photosynthetic rate was sensitive to deficit irrigation,which could quickly reflect the water status of sugar beet.(3)During regulated deficit irrigation in canopy development stage,the root volume and lateral root index both decreased.After irrigation the root volume of each treatment increased to a certain extent,but the root dry weight and root volume of T3 did not restored to the control treatment.The main and lateral roots of sugar beet responded differently under regulated deficit irrigation,the total root length,surface area,diameter,and volume of roots near the surface(0-10cm)decreased while the deep roots(20-40cm)diameter increased of T2 treatment.Lateral roots surface area near the soil surface increased of T3 treatment.(4)The changes of non-structural carbohydrates and key enzymes of sucrose metabolism were consistent under different regulated deficit irrigation.During regulated deficit irrigation in canopy development stage,the root total soluble sugar and sucrose contents of T2 treatment increased significantly,and the root glucose contents of T3 treatment increased significantly.After irrigation only the glucose content of the leaves and roots of T2 and T3 treatments returned to the control level,and which in T3 treatment was higher than that of T1 and T2 treatment.Moderate regulated deficit irrigation during canopy development stage significantly increased roots SS and reduced SPS activity,and severe regulated deficit irrigation decreased the root SS and SPS activities.After irrigation the activity of root SS and SPS of T2 and T3 treatments returned to the control level,while the activity of INV decreased greatly.【Conclusion】Under drought stress,the photosynthetic activity of sugar beet leaves was influenced firstly,which was significant lower in severe water deficit than that of moderate water deficit.Sugar beet adapted to deficit irrigation by reducing the leaf number,photosynthetic rate,storage root capacity and lateral root density.After irrigation leaf photosynthesis and storage root capacity increased differently.Under severe regulated deficit irrigation,roots area near the surface(0-10cm)increased,carbohydrates were preferentially supplied to the aboveground which ultimately leads to yield declined.Under moderate regulated deficit irrigation,deep(20-40cm)lateral root diameter increased,carbohydrates preferentially supplied to the underground which ultimately leads to yield and sugar production increased.