Physiological and Agronomic Mechanisms Involved in ‘Source–Sink’ Relationship in the High-Yield Population of Weak-Gluten Wheat

In order to provide a theoretical basis and technical approach for the construction and regulation of medium- and high-yield population cultivation practice of wheat after rice, agronomic and physiological characteristics in medium-high yielding populations were investigated by setting different basic seedlings and cutting leaves and ears with isotope tracing method in week-gluten wheat (Ningmai 29). The results showed that the medium-high yield (yield above 7500 kg/km2) group could be achieved at medium densities (150 × 104/hm2 and 225 × 104/hm2), whose populations own suitable number of spikes, higher grain number per spike and thousand-grain weight (the larger and stronger ‘sink’). Meanwhile, these two medium-high yielding populations had higher leaf area index and suitable light-transmission rate after anthesis; thus, the leaf net photosynthetic rate after anthesis was higher, and the capacity of carbon assimilates was stronger. From the 15N test, it can be seen that the relationship between individuals in the medium-high yielding population (medium-density) is more harmonious, and the plant had higher nitrogen utilization efficiency. More nitrogen is concentrated in the spike at maturity. The results of the 13C pot trials showed that the top-three functional leaves had a higher capacity for source-production, which was also the main source of post-flowering assimilates. Increasing their area to improve the ‘source–sink’ ratio would help coordinate the ‘source–sink’ relationship in the group with a stronger ‘sink’. The main technical approach is to increase the area and duration of the upper-three functional leaves after anthesis on the basis of a larger sink, thus ensuring a higher source–sink ratio and a harmonious ‘source–sink’ relationship after flowering.