Tp. Garnett et al., Simultaneous measurement of ammonium, nitrate and proton fluxes along the length of eucalypt roots, PLANT SOIL, 236(1), 2001, pp. 55-62
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.