[Physiological processes and major regulating factors of nitrogen uptake by plant roots]

Soil nitrogen (N) is one of the mineral elements absorbed in large amount by plant roots, while global change could affect its availability, and furthermore, affect the carbon (C) allocation in terrestrial ecosystem. Therefore, the study of plant root N uptake and regulation becomes an important issue in predicting the structure and function of ecosystem. In the biosphere, plants are exposed to different N forms, and long-term biological evolution and environmental adaptation resulted in a significant distinction of plant root N uptake regions and metabolic processes, as well as the regulation of the N uptake. However, plant has formed different mechanisms and strategies for N uptake, because of their living in the soil with dominant sole N form for generations. In this paper, the research advances on how plant root absorbs N and which factors control the N absorption processes were reviewed, with the biological availability of different soil N forms (nitrate, ammonium and organic N), N uptake regions in root, N loading and transport in xylem, and uptake mechanisms of different N forms emphasized. The signal regulation of N uptake and the effects of environmental factors were also considered. Several issues about the present researches on plant root N uptake were discussed.