The dynamics of nitrate (NO3-), a major nitrogen (N) source for natural plants, has been studied mostly through experimental N addition, enzymatic assay, isotope labeling, and genetic expression. However, artificial N supply may not reasonably reflect the N strategies in natural plants because NO3- uptake and reduction may vary with external N availability. Due to abrupt application and short operation time, field N addition, and isotopic labeling hinder the elucidation of in situ NO3--use mechanisms. The concentration and natural isotopes of tissue NO3- can offer insights into the plant NO3- sources and dynamics in a natural context. Furthermore, they facilitate the exploration of plant NO3- utilization and its interaction with N pollution and ecosystem N cycles without disturbing the N pools. The present study was conducted to review the application of the denitrifier method for concentration and isotope analyses of NO3- in plants. Moreover, this study highlights the utility and advantages of these parameters in interpreting NO3- sources and dynamics in natural plants. We summarize the major sources and reduction processes of NO3- in plants, and discuss the implications of NO3- concentration in plant tissues based on existing data. Particular emphasis was laid on the regulation of soil NO3- and plant ecophysiological functions in interspecific and intra-plant NO3- variations. We introduce N and O isotope systematics of NO3- in plants and discuss the principles and feasibilities of using isotopic enrichment and fractionation factors; the correlation between concentration and isotopes (N and O isotopes: delta O-18 and Delta O-17); and isotope mass-balance calculations to constrain sources and reduction of NO3- in possible scenarios for natural plants are deliberated. Finally, we offer a preliminary framework of intraplant delta O-18-NO3- variation, and summarize the uncertainties in using tissue NO3- parameters to interpret plant NO3- utilization. Publication name | FRONTIERS IN PLANT SCIENCE, 5 10.3389/fpls.2014.00355 JUL 23 2014 | Author(s) | Liu, Xue-Yan; Koba, Keisuke; Makabe, Akiko; Liu, Cong-Qiang | Corresponding author | LIU Xueyan liuxueyan@vip.skleg.cn 1. Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China 2. Tokyo Univ Agr & Technol, Inst Agr, Dept Environm Sci Biosphere, Fuchu, Tokyo 183, Japan | View here for the details
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