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 (a), cereals (wheat and rice) (b), Western candle tree Banksia prionotes (c), castor bean (d), sunflower (e), and Arabidopsis (f). (g) Summary of hypothetical roles of nitrate circulation via phloem sap (see text for further details).