MECHANISMS OF ADAPTATION OF PLANTS TO ACID SOILS

Major constraints for plant growth on acid mineral soils are toxic concentrations of mineral elements like Al, of H+, and/or low mineral nutrient availability either as a result of solubility (e.g. P and Mo), low reserves, and impaired uptake (e.g. Mg2+) at high H+ concentrations. Inhibition of root growth particularly by Al leads to more shallow root systems, which may affect the capacity for mineral nutrient acquisition and increase the risk of drought stress. Of the two principal strategies (tolerance and avoidance) of plants for adaptation to adverse soil conditions, the strategy of avoidance is more common for adaptation to acid mineral soils. Examples are (i) root-induced changes in the rhizosphere such as pH increase, (ii) release of chelators for Al, higher activity of ectoenzymes (acid phosphatases), and (iii) increase in root surface area via mycorrhizae. In order to have a better understanding of the principles of the mechanisms by which plants adapt to acid mineral soils more attention should thus be given to conditions at the root-soil interface.