Natural and anthropogenic stress in spruce and beech ecosystems in the Solling project

The investigations show that low Ca/Al-ratios in mineral soil horizons cause a shallow root system with spruce. But obviously other soil conditions expect acidification can also be responsible for a shallow root system. Additional investigations and field experiments have to find out the driving forces. A new phenomenon in fine root investigations are the low fine root concentrations in the uppermost mineral soil horizons. It is to be observed with spruce as well as with beech in stands with strong acidification of the top soil. Further experiments are needed to evaluate what are the main chemical variables (pH, heavy metals etc.) In this way soil acidification can cause reductions of fine root biomasses in subsoils as well as in uppermost soil horizons. These reductions can influence the response of trees to water stress. Relations to the symptoms of needle losses with spruce are likely. The close correlations between the chemistry of the soil, the roots and the needles indicate, that the yellowing symptoms of spruce trees, which were related to Mg-deficiency, are caused by Mg-deficiency in the soil. It is to be emphazised that it is not a pure Mg-deficiency. Ion antagonism to Al and especially to H in connection with fine root distribution are of main importance. (orig.)