Measurements of NH4+ and NO3– root acquisition capacity with N-13 radiotracer in roots of late-successional conifers reveal a strong preference for NH4+-nitrogen and limited capacity to access NO3—nitrogen from soil (Kronzucker et al., 1997, Nature 385,59). Plant roots differ in their adaptation to the NH4+ or NO3– sources of nitrogen, which can determine plant distribution patterns in ecology (Britto & Kronzucker, 2002, Journal of Plant Physiology 159, 567; Kronzucker et al., 2003, Physiologia Plantarum 117, 264).