Regulation of lignin composition by nitrogen rate and density and its relationship with stem mechanical strength of wheat

Increasing wheat yield is one of the effective ways to guarantee food security. In the current field production, dense planting with reasonable nitrogen is the most direct and efficient technique to achieve high yield. However, lodging, caused by overly large population with improper nitrogen management, has been a major limiting factor of grain production. In the present study, we comprehensively evaluated the composition and distribution of lignin monomers in stems and its relationship with mechanical strength. The results showed that syringyl (S) monomers were the predominant lignin monomeric units with enhancing mechanical strength. The reduction in the content of S subunits and total lignin, and the increased proportion of p-hydroxyphenyl (H) subunits were the crucial factors of low breaking strength of stems at high planting density and nitrogen fertilizer consumption. Furthermore, we speculated that bioengineering transformation and cultivation measures could be used to modify lignin composition and achieve high yield and high efficiency of wheat.