Effects of Deficit Irrigation on the Photosynthetic and Physiological Characteristics of Leaves and Yield of Isatis tinctoria

Taking the Isatis tinctoria as research crop, the field water control experiment was carried out in an arid oasis of the middle of the Hexi Corridor in 2018, and deficit levels included slight, moderate, severe water deficit (WD) and suitable irrigation, the influences of WD on physiological parameters, irrigation volume, yield and quality of Isatis tinctoria were studied with drip irrigation and plastic mulch, which would provide the theoretical basis for the establishment of irrigation management strategy of I. tinctoria in Hexi area. The results showed that WD treatment during the vegetative and fleshy root growth stages reduced the leaf photosynthetic rate (P_n), transpiration rate (T_r), and stomatal conductance (G_s), and with the higher degree of WD, the greater the decrease. Slight WD treatment had no significant effects on leaf photosynthetic capacity, and yield as compared with control, but the rest of treatment led to varying degrees of decrease in leaf photosynthetic capacity and yield. Fitting the relationship between the irrigation amount and the yield showed a quadratic parabola, which demonstrated that the yield did not enhance along with the increase of the irrigation amount. In conclusion, under-mulched drip irrigation WD reduces photosynthetic capacity of I. tinctoria leaves, while slight WD irrigation applied during the vegetative growth period saves irrigation water and improves yield and irrigation water use efficiency.