Plants, Nutrients and Australian Soils

The main conclusion that can be drawn from this series of experiments is that the acid population is limited in its growth on the calcareous soil because of that soil's high pH, which severely limits the availability of Fe. We might also deduce that the calcareous population has either a lower absolute requirement for Fe or is in some way genetically better equipped to solubilize Fe from the calcareous soil.

In fact, it has been demonstrated in some agricultural plants that a single gene can determine a plant's sensitivity to low solubility of Fe in alkaline soils (see the accompanying photo of both sensitive and tolerant soybean plants). Tolerant plants are able to reduce ferric (Fe³⁺) to ferrous (Fe²⁺) at the root surface. Fe²⁺ is more soluble at high pH and therefore more readily available to the plant. Thus, in the future, new agricultural plants might be developed to overcome Fe or other mineral deficiency or toxicity problems through genetic engineering.

Two soybean plants grown in a glasshouse under identical conditions on an alkaline soil.

The non-susceptible plant shows comparatively healthy green leaves.

The susceptible plant shows severe leaf chlorosis (note that some of the newer leaves are tinged with green and that some of the lower leaves have been shed).