Chemical Stress - Nature of the solutes
The acidic or basic reaction of soil and water of a particular habitat reflects its geochemical history beginning with its formation and subsequent interactions with other constituents of the earth up to its current chemical activities. Mineral deposits in their oxide form ('Bhashma') are usually basic in their reaction. The reaction of chloride, sulphate and nitrate is acidic or neutral depending upon the nature of the conjugate ions.
You can visualise the reaction of a salt through its acidic and basic radicals. On a natural course, one would expect the neutralisation reactions and consequently change in the character of the habitat towards neutral. However, there are soils which are very high and others very low in pH and certain plant species survive in such soils.