Cation concentrations of short roots of Norway spruce as affected by acid irrigation and liming

The longterm effect of acid irrigation and Liming (dolomitic limestone) on the mineral element content of roots of Norway spruce (Picea abies [L.] Karst.) was investigated in an 80-year-old Norway spruce stand in South Germany (Bavaria). Soil cores of four soil depths (humic layer, 0-10, 10-20 and 20-30 cm) were taken over 2 years (August 1991 and August 1992) from six plots with different treatments (control, normal irrigation, acid irrigation solely or in combination with liming) and living short roots selected and analysed for calcium (Ca), magnesium (Mg), manganese (Mn) and aluminium (Al). On the acid irrigated plot, the Ca and Mg contents of roots were decreased in 1991, but by 1992, 2 years after the irrigation had been terminated, no difference could be found. The Al content of the roots was not increased by acid irrigation but rose with increasing soil depth, regardless of treatment. Liming increased root contents of Ca and Mg and reduced contents of Mn and Al. This effect was especially distinct in the humic layer and decreased with increasing soil depth. Even though the molar Ca/Al-ratio in the roots in the mineral soil was generally low (0.09-0.52), no evidence of Al toxicity could be found. The formation of Al complexes is discussed as a reason for this behaviour.