Comparative kinetic analysis of ammonium and nitrate acquisition by tropical lowland rice: implications for rice cultivation and yield potential

Nitrogen limitation compromises the realization of yield potential in cerea ls more than any other single factor. In rice, the world's most important c rop species, the assumption has long been that only ammonium-N is efficient ly utilized. Consequently, nitrate utilization has been largely ignored, al though fragmentary data have suggested that growth could be substantial on nitrate. Using the short-lived radiotracer N-13, we here provide direct com parisons of root transmembrane fluxes and cytoplasmic pool sizes for nitrat e- and ammonium-N in a major variety of Indica rice (Oryza sativa), and sho w that nitrate acquisition is not only of high capacity and efficiency but is superior to that of ammonium. We believe our results have implications f or rice breeding and molecular genetics as well as the design of water-mana gement and fertilization regimes. Potential strategies to harness this hith erto unexplored N-utilization potential are proposed.