SENSITIVITY OF PLANTS TO ACIDIC SOILS EXEMPLIFIED BY THE FOREST GRASSBROMUS-BENEKENII

The aim of this paper is to study the role of Al- and H-ions, base cat ion deficiency and N-nutrition as solely NH4 in disturbing plant growt h on acid soils. Effects of these factors on growth of the forest gras s Bromus benekenii were studied experimentally and in the field and co mpared to other deciduous forest plants. Bromus benekenii is most freq uent at pH >4.5 (soil solution) and absent at pH 3.8. In a pot experim ent using an acid soil of pH 3.3, raised by steps to pH 5.2 by carbona te addition, growth of Bromus benekenii and nine other species (out of 17) was limited at pH <4.1. Toxicity of H-ions to Bromus benekenii wa s confirmed in a solution experiment at pH less than or equal to 4.2. Al-toxicity occurred at low Al-concentrations (20 CIM) in Bromus benek enii and nine other tested species. Base cation (Ca+Mg) mitigation of Al-toxicity was found in a factorial solution experiment. Our experime nts also indicate that H- and Al-ions interact in a way that makes com bined treatments equally toxic as concentrations of H- or Al-ions alon e. Incubation experiments showed that soil nitrification is retarded i n acid soils. This may affect Bromus benekenii as it was most demandin g on NO3-availability out of 15 species in a solution experiment. Only 50% growth was attained in a NH4- as compared to a NH4+NO3-treatment. Comparing experimental results with field data, we conclude that H- a nd Al-toxicity and unfavourable N-nutrition (as solely NH4) to a simil ar extent may explain the acidifuge behaviour of field layer plants.