Response of Root Morphology to Nitrate Supply and its Contribution to Nitrogen Accumulation in Maize

Selection for nitrogen (N)-efficient crops is considered to be an effective approach for minimizing the input and the loss ofNfertilizers in agricultural fields. This study investigated the hypothesis that nitrate supply may induce changes in root morphology so that N uptake efficiency can be influenced. Different levels of nitrate concentration (0.04, 0.2, 2, and 4mM)were supplied to five maize (Zea mays L.)inbred lines that had shown different N efficiencies. Possible correlations between N-uptake efficiency and several root parameters of root morphology were evaluated. The two N-efficient varieties, 478 and H21, had higher shoot and root weight and absorbed more N than the two N-inefficient lines, Wu312 and Zong31, especially under low N supply. In general, high nitrate levels (2 and 4mM)increased the total length of lateral roots (LR), but limited the total length of primary roots (PR)(including seminal and nodal roots)as well as the average length of primary roots. As a result, the total root length (TR)increased with the increasing of nitrate levels. TotalNaccumulation had significant positive correlations with the root dry weight, TR, and PR at low N supply (0.04-2 mM). At high N supply (4 mM), however, only LR was to some extent correlated to N accumulation. It is concluded that, under N deficient situation, a larger root system (total root length and root surface area)that resulted mainly from the longer primary roots contributed to the efficient N accumulation. At sufficient N supply, longer lateral roots are the main factor contributed to N accumulation.