The mineral nutrition of heather on calcareous soil.
Ericaceous plants grow preferentially on soils with a low pH, and generally perform
poorly in areas with high pH calcareous soils. The reasons for the calcifuge behaviour
of species of one genus, Erica, was studied in a calcareous rendzina collected from the
South Downs, with a view to identifying physiological characteristics which could be
used to select for improved lime-tolerance in the Ericaceae.
Varieties of E. carnea and E. x darleyensis were shown to be relatively resistant to
chalk-soil compared with varieties of E. vagans. In soil-based screening experiments, E.
vagans 'Lyonesse' and 'Mrs D. F. Maxwell' rapidly developed severe foliar chlorosis, or
lime-induced chlorosis, and their growth in soil was depressed by up to 7-fold compared
with plants in an acid (pH 4) peat compost. E. carnea and E. x darleyensis varieties
were resistant to chlorosis and remained green in chalk soil. The addition of nutrients
(NPK and trace elements) increased the growth of the lime-resistant varieties in both
peat and chalk soil.
In nutrient solution, the source of nitrogen (nitrate or ammonium ions) had little effect
on the growth of either lime-resistant or lime-sensitive varieties, although some varieties
performed better when a component of the N was in the form of N03'. In an Fe-free
nutrient solution, 1 mM NaHCO3 markedly reduced the root and shoot growth of both
lime-tolerant and sensitive varieties. The clear differences between lime-resistant and
lime-sensitive varieties found in soil experiments were not apparent with NaHCO3 in
solution culture indicating that low concentrations of bicarbonate in nutrient solution
may not be an appropriate method of screening for improved lime-tolerance in Erica.
Bicarbonate and high pH in nutrient solution depressed the uptake of the radioisotopes
59Fe and 86Rb in both lime-resistant and lime-sensitive cultivars.
Iron deficiency, induced by withholding Fe in nutrient solution, resulted in an elevated
rate of root Fe(III)EDTA (ethylenediaminetetraacetic acid) reduction compared with Fesufficient
plants. The maximum induced Fe(III)EDTA reduction rate (Vn,. ) of limeresistant
cultivars (0.96-0.107 pmol. g"' FWT. h'') was lower than that of lime-sensitive
varieties (0.125-0.404 tmol. g' FWT. h-1), suggesting that roots of lime-sensitive
varieties have a greater capacity for Fe absorption than lime-tolerant varieties.
Spraying or watering with Fe chelate (FeEDDHA - ethylenediamine di(ohydroxyphenylacetic
acid)) remedied chlorosis in the lime-sensitive varieties and
increased leaf chlorophyll by up to six fold and whole plant biomass by up to two fold.
Chlorosis was associated with a reduced concentration of o-phenanthroline-extractable
('active') Fe, and a high concentration of total Fe, compared with green tissue.
It is concluded that in chalk soil, lime-induced chlorosis, caused by the immobilisation
of Fe in the shoot and a reduction in 'physiologically active' Fe in the leaf tissue,
characterises lime-sensitive heather varieties. Resistance to chalk soil in Erica appears
not to be related to root physiology. Rather the ability to transport and distribute Fe
within the shoot under calcareous conditions is a major factor contributing to limeresistance