2.7 Measurement of total N content and15N-NO3− absorption
Total N content was measured as described by Makino et al. (1997).
NO3− quantitation in plant tissue was
measured with high performance liquid chromatography (Agilent
Technologies, USA) (Patterson et al. , 2010).15N-NO3− uptake
activity was determined on an isotope-ratio mass spectrometry system
(Thermo Scientific, USA) and15N-NO3− influx rate
was calculated based on the amount of 15N taken up per
unit weight of the sample per unit time (Zhang et al. , 2021).