Evidence for a nutritional disorder of Oxalis acetosella L. on acid forest soils. I. Control situation and effects of dolomitic liming and acid irrigation

This paper reports on the mean cover, biometric and vitality parameters and mineral nutrient status of wood-sorrel (Oxalis acetosella L.) on the control and experimental plots of a mature Norway spruce stand on acid soil (Hoglwald Experiment). On the control plot Oxalis showed relatively poor leaf growth and chloroses on young and older leaf blades. Mineral analyses in the Hoglwald and comparative studies on other forest sites indicated a very good to good supply of N and P, a moderate Ca nutrition and very high Mn concentrations of the leaves. The input of dolomitic lime led to a drastic propagation and vitalization of the wood-sorrel. The long-lasting effect of treatment was independent of pH dynamics in the root zone. The leaf chloroses of Oxalis disappeared completely after that treatment. The level of Ca and Mg supply clearly improved, whereas the concentrations of P, N, Mn and Zn diminished. Surprisingly, the K nutrition also improved after liming. Oxalis reacted to acid irrigation (sulfuric acid; pH 2.7-2.8) in comparison to normal watering (pH 5.0-5.5) with a continuous decrease in cover, but without visible leaf necroses. The concentrations of total sulphur, SO₄-S and S(org) were raised, while the concentrations of Ca, Mn and Zn of the leaf blades decreased. After termination of acid input a recovery of nutrition occurred and a slow recolonization began. Preceding lime application prevented the growth-inhibiting effect of the acid irrigation. The study leads to the working hypothesis, that Ca nutrition may be the controlling factor for leaf growth and vegetative propagation of Oxalis in the Hoglwald Experiment.