A RootNav analysis of morphological changes in Brassica napus L. roots in response to different nitrogen forms

Root architecture impacts the capacity of plants to access nutrients and water. By using the RootNav package, comprehensive morphological changes in root system architecture in response to different nitrogen concentrations and sources were investigated in Brassica napus. Ten-day-old seedlings showed a decrease in total root length, lateral root (LR) density and root exploration area with increasing external NO3− concentrations from 0.5 to 10 mM. The application of 0.5 mM NO3− induced more branching in the root system relative to the treatments with higher NO3− concentrations. The allocation of biomass into the root was greater in the low NO3− treatment relative to the high NO3− treatments, reflecting the fact that plants invested more resources in their roots when N uptake from the environment was limited. High NH4+ concentration (10 mM) led to a stunted root system in B. napus, which showed a decrease in primary root (PR) length, total root length, LR branching zone, LR density and root exploration area. Increasing l-glutamate concentration from 0.01 to 0.1 mM suppressed PR length and total root length, whilst the LR branching zone did not change in the different l-glutamate treatments, suggesting that l-glutamate even at micromolar level could arrest PR growth and LR growth in B. napus. In conclusion, external N availability induced changes in the overall root morphology, with root elongation decreasing under an extremely N impoverished environment, but increasing under relatively mild N deficiency (for both NO3− and NH4+).