根系氮吸收过程及其主要调节因子

氮（N）是植物根系吸收最多的矿质元素之一．全球变化将使土壤中N的有效性发生改变，影响陆地生态系统碳分配格局与过程．研究根系N吸收及其调控对预测生态系统结构和功能具有重要理论意义．由于土壤中存在多种形态的N源，长期的生物进化和环境适应导致植物根系对不同形态N的吸收部位、机理及调控有较大差别．因此，植物长期生长在以某一形态N源为主的土壤上就形成了不同的N吸收机制和策略．本文简述了近年来在植物根系N吸收和调控方面的最新研究进展，重点评述了不同形态N在土壤中的生物有效性，根系N吸收部位，N在木质部中的装载和运输，不同形态N（NO3^-、NH4^＋和有机氮）的吸收机制，以及根系N吸收的自身信号调控和环境因子对根系N吸收的影响．在此基础上，提出了目前根系N吸收研究中存在的几个问题．

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.