Phytosiderophore (PS) release occurs under both iron
and zinc deficiencies in representative Poaceae and has been
speculated to be a general adaptive response to enhance the
acquisition of micronutrient metals. We tested this
hypothesis within an on-going study of the role of micronutrient
metal nutrition for patterns of spontaneous
vegetation in relation to soil pH and carbonate content.
Hordelymus europaeus (L.) Harz, a negative grass species
commonly found on soils rich in CaCO3 in Western Central
Europe, was subjected to deficiencies of Fe, Zn, Mn
and Cu using chelator-buffered nutrient solutions. PS
release rates were determined at 3–5 d intervals during onset
and development of deficiency symptoms. Plant dry matter
yields and nutrient concentrations, measured at three
time points were used to construct growth curves for calculation
of PS release per unit root mass. In comparison
with trace metal-sufficient control plants, dry matter production
was markedly reduced in the Fe, Zn, Mn and Cu-deficiency treatments,
with final relative yields of 6, 11, 15
and 31%, respectively. The phytosiderophore
produced under Fe- and Cu-deficiency treatments was identified,
using HPLC, as desoxymugineic acid. The
highest rate of PS release (18 μmol g−1
root d. wt in 2 h) was measured in the Fe-deficiency treatment, and there
was substantial release in the Cu-deficiency treatment (7·25 μmol
g−1
root d. wt in 2 h). No PS release above
control levels (2·6 μmol g−1
root d. wt in 2 h) was observed in the Zn- or Mn-deficiency treatments
(1·5 and
2·6 μmol g−1
root d. wt in 2 h, respectively). It remains to be
clarified whether PS release in response to Cu
deficiency is a primary reaction to the deficiency, or
is caused by a chain of events similar to that observed in
Zn-deficient wheat, which involves internal Fe deficiency.
Our results suggest that PS release in the native plant
species H. europaeus is a specific response to Fe and Cu
deficiency and is not significantly induced in response to
deficiencies of Zn and Mn. Induction of the PS mechanism
in different plant species might be more diverse than previously thought.