EVIDENCE FOR A NUTRITIONAL DISORDER OF OXALIS-ACETOSELLA L. ON ACID FOREST SOILS - II - DIAGNOSTIC FIELD EXPERIMENTS AND NUTRIENT SOLUTION STUDIES

Different field experiments were performed to discover the main factor (s) responsible for the poor leaf growth, moderate propagation and lea f chlorosis of Oxalis acetosella in an old Norway spruce stand with ac id soil (Hoglwald Forest). A previous study had suggested, that Ca (or Mg) deficiency or Mn toxicity could be involved. In a Main Diagnostic Field Experiment with an intact population, Ca and Mg were either app lied as sulphate or carbonate to distinguish between nutritional and p H effects. Mn and Si were also applied to aggravate or overcome possib le effects of Mn toxicity. Enhancement experiments with different amou nts of CaSO4 were conducted to investigate the Ca dose-effect relation ship under field conditions. Additional trials with SrCO3, BaCO3 and N aHCO3 had the goal to raise the soil pH without supply of nutrients. G reenhouse experiments with Oxalis acetosella supplemented the field st udies by investigating the Ca and Mn dose-effect relationships under c ontrolled conditions. Growth, vitality and nutrition of Oxalis were st udied in a nutrient solution culture at pH 4.0 over a range of concent rations of Ca (20 to 5000 mu mol L-1) and Mn (5 to 1000 mu mol L-1) re spectively. Furthermore, the effects of two contrasting ammonium/nitra te ratios were tested. The nutritional composition of the basal nutrie nt solution and the microclimate in the greenhouse were as far as poss ible adjusted to the environmental conditions of the plant in the Hogl wald Forest. All these studies led to the conclusion, that the moderat e growth and vitality of Oxalis in the Hoglwald Forest was mainly due to an insufficient Ca supply, rather than an effect of Mg deficiency, low soil pH or Mn toxicity. The application of CaSO4 caused a similar stimulation of the growth as CaCO3. A clearly positive, close CaSO4 do se-effect relationship was detected in field experiments as well as in the nutrient solution study. The same type of leaf chloroses as in th e field was reproduced through low Ca nutrient solutions. Predominant ammonium nutrition may significantly impair Ca uptake. Oxalis acetosel la displayed a relatively high leaf tissue tolerance of excessive Mn. There was no indication for a Mn-induced Ca deficiency in the Hoglwald Forest. Enhanced Si uptake led to a partial vitalization of Oxalis; t he reason for that remained unclear.