Non-uniform wheat population distribution enhances wheat yield and lodging resistance synchronously

Film mulching ridge-furrow planting (RF) planting is an important dry farming mode for wheat but it usually causes lodging, which depends on lignin accumulation in the stems. Previous research has generally speculated that lignin synthesis is influenced by the light environment, which can be modified by regulating the population distribution. However, whether light is the main factor affecting lignin accumulation has yet to be determined. Meanwhile, the impact of light-based regulation on lodging suppression and the specific mechanism involved are still unclear, especially under RF conditions. Thus, we investigated the effects of regulating the population distribution on the occurrence of lodging in wheat to clarify the mechanism associated with lodging resistance and to develop approaches for improving lodging resistance under RF. This three-year field experiment investigated the effects of four treatments on lodging occurrence in wheat: traditional flat planting treatment (TF, row spacing of 20 cm), RF + uniform wheat population distribution (RF20, row spacing of 20 cm:20 cm:20 cm), and RF + non-uniform population distribution (RF25, row spacing: 25 cm:10 cm:25 cm; RF30, row spacing: 15 cm:30 cm:15 cm). Compared with TF, RF20 significantly increased the occurrence of lodging, whereas RF25 and RF30 could effectively reduce the occurrence of lodging and increase wheat yield, in which the effect of RF30 was optimal. The photosynthetically active radiation (PAR) in the middle–lower layers of the canopy was significantly reduced under RF20, whereas RF25 and RF30 effectively improved PAR. Mechanical stem parameters comprising the filling degree, section modulus, breaking strength, and lodging resistance index were significantly lower under RF20 than TF, whereas these parameters improved significantly under RF25 and RF30. In addition, lignin accumulation and the activities of lignin biosynthesis enzymes and related gene expression levels were significantly lower under RF20 compared with TF, whereas these parameters were significantly higher under RF25 and RF30. Correlation and path analyses showed that the canopy light environment was related to lignin biosynthesis in the stems, and thus lodging resistance. The canopy light environment was undesirable under RF with a uniform population distribution, where it significantly reduced the mechanical properties of the stems and lodging resistance. Regulating the population distribution can enhance the mechanical properties of the stems by improving the canopy light environment to promote the synthesis and accumulation of lignin in the stems to reduce lodging in wheat. These findings may provide a theoretical basis for understanding the lower stem strength in wheat under RF and help the development of suitable measures for enhancing lodging resistance.