Mixed cropping increases grain yield and lodging resistance by improving the canopy light environment of wheat populations

The primary technical way to increase wheat yield is to increase planting density. However, the dense planting population has poor stem development quality due to intensified resource competition, ultimately leading to an increased lodging risk. Mixed cropping can take advantage of the genetic diversity of cultivars to solve the contradiction between lodging traits and yield in dense planting wheat populations. Nevertheless, its resistance mechanism to lodging and yield increase still needs to be studied in depth. Here, we conducted a field experiment in the North China Plain using a lodging-resistant cultivar, Shannong 28 (SN28) and a lodging-sensitive cultivar, Shannong 16 (SN16), as test materials to study the effect of mixed cropping on the crop yield by setting 3 planting densities: 225 plants m-2 (D1), 375 plants m-2 (D2), and 525 plants m-2 (D3). We studied the effect of mixed cropping on the resistance of wheat population and yield. The results showed that the mixed sowing treatment (MIX) significantly improved the canopy light interception rate (8.99%) and net photosynthetic efficiency (11.02%) under dense planting conditions (D3). It improved stem quality by increasing the content of carbohydrates (lignin, cellulose and soluble sugar), on the other hand, contributing to yield by increasing grain weight. Meanwhile, the structural equation modeling validated the above results. Compared to SN16 sole cropping (SN16), SN28 sole cropping (SN28) and MEAN (average of the two varieties in sole cropping), MIX yield was significantly higher by 17.39%, 3.86% and 10.21%. These findings revealed that mixed cropping improved yields due to improved wheat denseness tolerance, reduced field lodging rate, and increased grain weight. Our study concluded that this could be a cultivation measure to effectively suppress the occurrence of wheat lodging from the perspective of adaptive changes in stem under dense planting populations, to provide a theoretical basis for wheat lodging resistance and yield increase.