Experimental evidence for the relative sensitivity of deciduous forest plants to high soil acidity

Thirteen species of deciduous forest vascular plants were established from seeds: Brachypodium sylvaticum, Carex sylvatica, Circaea lutetiana, Deschampsia flexuosa, Galium odoratum, Lamium galeobdolon, Lathyrus vernus, Luzula pilosa, Milium effusum, Poa nemoralis, Sanicula europaea, Stellaria holostea and Stellaria nemorum. An acid beech forest soil was variously treated with carbonates (CaCO₃ + MgCO₃ or SrCO₃) to obtain a soil solution pH of 3.3–5.2. The experimental results were compared with the field distribution of the same species in 230 south Swedish deciduous forests with regard to soil pH.

In general, the species reacted to increasing soil pH in accordance with their field distribution. Addition of SrCO₃ was almost equally effective as CaCO₃ + MgCO₃ (both at pH 4.2 in the soil solution) in promoting establishment and growth, whereas most species failed in the untreated soil (pH 3.3). There were no indications that the Ca or Mg concentrations of the soil solution were below minimum or even suboptimal for plant growth in the untreated soil. Within the pH range (pH 3.5–4.3) which proved critical to establishment and growth in most of the species, the reactive Al³⁺ concentration of the soil solution did not vary significantly. It is suggested that the high acidity of the rhizosphere solution, possibly aggravated by Al³⁺, obstructed the uptake or retention of mineral nutrients by the roots in the untreated acid beech forest soil.