摘要：

Different field experiments were performed to discover the main factor(s) responsible for the poor leaf growth, moderate propagation and leaf chlorosis of Oxalis acetosella in an old Norway spruce stand with acid 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 applied as sulphate or carbonate to distinguish between nutritional and pH effects. Mn and Si were also applied to aggravate or overcome possible effects of Mn toxicity. Enhancement experiments with different amounts of CaSO4 were conducted to investigate the Ca dose-effect relationship under field conditions. Additional trials with SrCO3, BaCO3 and NaHCO3 had the goal to raise the soil pH without supply of nutrients. Greenhouse experiments with Oxalis acetosella supplemented the field studies by investigating the Ca and Mn dose-effect relationships under controlled conditions. Growth, vitality and nutrition of Oxalis were studied in a nutrient solution culture at pH 4.0 over a range of concentrations of Ca (20 to 5000 mu mol L-1) and Mn (5 to 1000 mu mol L-1) respectively. Furthermore, the effects of two contrasting ammonium/nitrate ratios were tested. The nutritional composition of the basal nutrient solution and the microclimate in the greenhouse were as far as possible adjusted to the environmental conditions of the plant in the Hoglwald Forest. All these studies led to the conclusion, that the moderate 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 dose-effect relationship was detected in field experiments as well as in the nutrient solution study. The same type of leaf chloroses as in the field was reproduced through low Ca nutrient solutions. Predominant ammonium nutrition may significantly impair Ca uptake. Oxalis acetosella 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; the reason for that remained unclear.

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