Changes in root size and distribution in relation to nitrogen accumulation during maize breeding in China

Modern maize breeding has increased maize yields worldwide. The changes in above-ground traits accompanying yield improvement are well-known, but less information is available as to the effect of modern plant breeding on changes in maize root traits. Root growth, nitrogen uptake, dry matter accumulation and yield formation of six maize hybrids released from 1973 to 2000 in China were compared. Experiments were conducted under low and high nitrogen supply in a black soil in Northeast China in 2010 and 2011. While nitrogen accumulation, dry matter production and yield formation have been increased, modern maize breeding in China since 1990 has reduced root length density in the topsoil without much effect on root growth in the deeper soil. The efficiency of roots in acquiring N has increased so as to match the requirement of N accumulation for plant growth and yield formation. The responses of root growth, nitrogen and dry matter accumulation, and grain yield to low-N stress were similar in the more modern hybrids as in the older ones. Modern maize breeding has constitutively changed root and shoot growth and plant productivity without producing any specific enhancement in root responsiveness to soil N availability.