Abstract:

By using the electric rainproof shed at Gucheng station in Hebei province, natural precipitation is covered and irrigation is artificially controlled to form soil waterlogging, high humidity, drought and control. After summer maize flowering, the grain filling process, above-ground biomass, yield components, root-shoot structure and root-shoot ratio are measured. To explore the effects of soil drought and waterlogging stress on grain filling and yield formation of summer maize without the influence of rain and low-temperature stress. Analyze the source-sink relationship of dry matter in summer maize grain filling. The results show that the response of grain filling of summer maize to drought and waterlogging stress are different. The duration of filling days are longer under waterlogging (7-8 d longer than control) and shorter under severe drought (5-6 d shorter than control). For average grain filling rate, they are 9.19%-9.85% higher than control for high humidity, 24.80%-25.26% lower than control for severe drought, and 6.89%-7.45% lower than control for moderate drought. The dry matter of summer maize grain filling mainly comes from the photosynthetic products formed by photosynthesis such as green leaves at the filling stage, while the dry matter accumulated in the vegetative growth stage is less transported and accumulated in the grain. Previous studies failed to clearly reveal the source-sink matching relationship of corn grain filling. The plants of summer maize are still green leafy living stems from maturity to harvest, and the photosynthetic capacity is also strong, and the straw stock is large during harvest, which leads to decrease in harvest index. The transfer volume and contribution rate of different vegetative organs on the above-ground of summer maize plants to grain filling are tested and analyzed. It was found that the contribution rate of different vegetative organs under drought and water stress is higher than control, but the economic yield is reduced, which indicated that the transfer volume and contribution rate of vegetative organs under drought and waterlogging stress could not really reflect the biological influence on the yield formation. Drought and waterlogging stress have different effects on photosynthetic physiological characteristics of ear leaves in summer maize filling stage. Net photosynthetic rate (P_n) is 0.91%-9.10% higher than the control under waterlogging, and 1.75%-9.13% lower than the control under high humidity. Drought is significantly lower than the control: 55.76%-59.08% lower in moderate drought, 92.16%-92.75% lower in severe drought. Drought has greater influence than high humidity. Leaf water use efficiency (WUE) is significantly decreased under severe drought condition, which is 60.40%-64.75% lower than control. Drought and waterlogging stress have negative effects on the formation of summer maize yield: the yield reduction rate of waterlogging and high humidity is 1.83%-8.43%, the yield reduction rate of drought treatment is 32.73%-81.96%, and the severe drought almost resulted in no harvest. The damage degree of drought is much greater than that of waterlogging and high humidity. Drought stress stimulated and induced the proliferation of fibrous roots in maize roots, and the weight of fibrous roots increased significantly, resulting in an increase in the root-shoot ratio. In particular, severe drought is more than 10 times higher than waterlogging, high humidity and control, indicating that maize roots, in particular, must have physiological regulatory mechanisms for emergency response to soil waterlogging stress and survival mechanisms to adapt to adverse conditions. Improve the function of absorbing water and nutrients, and enhance the support and lodging resistance of the root system to the plant. The research results provide data support and reference for assessing the effects of drought and flood disasters on crop growth and yield formation in northern arid regions, and taking agricultural measures to enhance the ability of disaster resistance and reduction and the coefficient of stable grain yield.

Key words: Summer maize, Root-shoot ratio, Filling rate, Waterlogging, Drought