Ad. Peuke et al., Foliar application of nitrate or ammonium as sole nitrogen supply in Ricinus communis - II. The flows of cations, chloride and abscisic acid, NEW PHYTOL, 140(4), 1998, pp. 625-636
Following a precultivation with pedospheric nitrogen nutrition, Ricinus pla
nts were supplied with nitrogen solely by spraying nitrate or ammonium solu
tion onto the leaves during the experimental period. The chemical compositi
on of tissues, xylem and phloem exudates was determined and on the basis of
the previously determined nitrogen flows (Peuke et al., New Phytologist (1
998), 138, 657-687) the flows of potassium, sodium, magnesium, calcium, chl
oride and ABA were modelled. These data, which permit quantification of net
-uptake, transport in xylem and phloem, and utilization in shoot and root,
were compared with results obtained in plants with pedospherically-supplied
nitrate or ammonium and data in the literature. Although the overall effec
ts on the chemical composition of supplying ammonium to the leaves were not
as pronounced as in pedospherically supplied plants, there were some typic
al responses of plants fed with ammonium (ammonium syndrome). In particular
, in ammonium-sprayed plants uptake and transport of magnesium decreased an
d chloride uptake was increased compared with nitrate-sprayed plants. Furth
ermore, acropetal ABA transport in the xylem in ammonium-sprayed Ricinus wa
s threefold higher than in nitrate-sprayed plants. Additionally, concentrat
ions of anions were more or less increased in tissues, particularly in the
roots, and transport fluids. The overall signal from ammonium-sprayed leave
s without a direct effect of ammonium ions on uptake and transport systems
in the root is discussed.