Simultaneous measurement of ammonium, nitrate and proton fluxes along the length of eucalypt roots

Knowledge of the preferred source of N for Eucalyptus nitens will lead to i mproved fertiliser management practices in plantations. Ion selective micro electrodes were used non-invasively to measure simultaneously net fluxes of NH4+, NO3- and H+ along the tap root of solution-cultured E. nitens. Measu rements were conducted in solutions containing 100 mum NH4NO3. The pattern of fluxes was such that there was a large influx of NH4+, a smaller influx of NO3- and large H+ efflux. The ratio of these fluxes was constant, accord ing to the ratio 3:1:-6 (NH4+:NO3-:H+). Within the region 20-60 mm from the root apex of E. nitens seedlings there was spatial and temporal variation in fluxes but flux patterns remained constant. Root hair density did not af fect fluxes nor did proximity to lateral roots. Variation was less than tha t found in previous studies of localised root fluxes using similar high-res olution measurement techniques. It was concluded that small-scale spatial v ariation in fluxes may have confounded previous studies. There were associa tions between fluxes of all three ions, the strongest associations being be tween NH4+ and H+, and NH4+ and NO3-. Overall, these results are consistent with NH4+ being the preferred source N for E. nitens.