It has been suggested that when ammonium
is supplied to plants, as compared to nitrate, this would save photo-energy, that is, 10 ATP (adenosine triphosphate) mol−1 N(Salsacet al., 1987). Total cost for NH+4 absorption, transport, reduction, and assimilation is almost 9.45 mol photon mol−1 N assimilated and transported (Raven, 1985).