Linking the physiological parameters of nitrate uptake with root morphology and topology in wheat (Triticum durum Desf.) and in citrus rootstock (Citrus volkameriana, Ten & Pasq)

The relationships between net nitrate uptake and root morphology and topology were investigated in wheat
(Triticum durum Desf.) and citrus (Citrus volkameriana Ten. & Pasq.) seedlings in which root systems were modified
by supplying different nutrient concentrations. Root morphological and topological changes were assessed by the number
of root tips, the total root length, and the topological index. The net nitrate uptake process was evaluated during
the induction and inhibition “feedback” regulation phases. In wheat seedlings, an increase in the external nitrate concentration,
at either high or no phosphate, brought about an increase in number of root tips but did not affect total root
length. A similar pattern was observed in citrus seedlings. Citrus seedlings also exhibited a shift in root branching pattern
from herringbone to dichotomous with an increase in the external nitrate concentration. Conversely, wheat root topology
was unaffected by nutrient treatments. A high level of nitrate supplied to wheat and citrus root systems reduced
the full induction of the nitrate uptake rate and cumulative nitrate uptake but increased the half-time of reaching the
full induction in net nitrate uptake (t1/2 kind). Finally, a negative correlation between number of root tips and t1/2 kind
was found in both species, while only in citrus seedlings was a positive correlation between t1/2 kind and the topological
index observed. The data suggest that root morphology has a greater effect on nitrate uptake than root topology.