Figure 1. Nitrate circulation via phloem sap : (a-f) Typical
species where phloem nitrate has been directly measured or inferred from
isotopic mass-balance: palm trees (van Die & Tammes, 1975) (a), cereals
(wheat and rice) (Hayashi & Chino, 1985; Hayashi & Chino, 1986) (b),
Western candle tree Banksia prionotes (Jeschke & Pate, 1995)
(c), castor bean (Peuke, 2010) (d), sunflower (Cui et al., 2020) (e),
and Arabidopsis (Wang & Tsay, 2011) (f). (g) Summary of processes
involving nitrate circulation via phloem sap (see text for further
details).