Effects of drip irrigation modes on activities of starch synthesis-related enzymes and accumulation of starch of kernels located in different ear positions of maize in the irrigation area of the Xiliaohe Plain

To explore the effects of drip irrigation modes on starch content and the activities of starch synthesis-related enzymes in spring maize at different grain positions in the irrigation area of the Xiliaohe Plain, the characteristics of starch accumulation and changes in the activities of adenosine diphosphate glucose pyrophosphorylase (AGPase), bound starch synthase (GBSS), and soluble starch synthase (SSS) at different grain positions were studied using ‘Nonghua 101’ as the test variety under mulch and shallow burial drip irrigation in 2019 and 2020. The results showed that the yield of shallow burial drip irrigation increased by 5.0% and 4.7% compared with mulch drip irrigation, and the 1000-grain weight increased by 7.4% and 6.9% from 2019 to 2020, in which grains in the middle ears improved by 7.7% and 4.1%, and in and upper ears by 10.8%, and 9.8%, respectively. The starch content, accumulation amount, and activities of synthesis-related enzymes of kernels located in different positions of spring maize ear were the lower part > the middle part > the upper part; the content and accumulation amount of starch under the two drip irrigation modes had little difference in the early stage, which were more advantageous in the upper part of the ear under shallow drip irrigation in the later growth stage. The activities of AGPase, GBSS, and SSS of shallowly buried drip irrigation were all higher than those of mulch drip irrigation in the late grain filling stage. The time to reach the maximum rate of starch accumulation in the middle and upper grains of the ear of the shallow burial drip irrigation was longer than that of the mulch drip irrigation, in which the active starch accumulation period was also longer, especially in the upper grains. The time to the maximum accumulation rate was delayed by 5.38 days, the average accumulation rate increased by 0.2836 mg·g⁻¹·d ⁻¹, and the final starch accumulation increased by 16.6%. Path and correlation analysis showed that the time to reach the maximum rate, the average accumulation rate, and the maximum accumulation rate had a great influence on the final starch accumulation. Starch synthesis-related enzymes activities were significantly positively correlated with the starch accumulation rate, which showed that the activity of starch-related enzymes in the kernels located in the middle and upper parts of the ear at the late grain filling stage was strong under shallow drip irrigation. The active accumulation period of starch was also longer, the time for the accumulation to reach the maximum rate was delayed, and the average accumulation rate was high, which was one of the reasons for the increase in grain weight and yield under shallow drip irrigation compared with mulch drip irrigation.